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chjmartin2
December 3rd, 2014, 06:36 AM
Hi,

Due to a wonderful Vintage Computer Forum member I now have the computer of my youth arriving! At some point in the past my parents had cleaned out our basement and threw it away. So, this computer has likely not been powered up in years. I want to give it the very best chance at life. What should I do first when it arrives? It is an 8088 TURBO 8.0 Mhz XT. I have the original keyboard and monitor already and now I will have the CPU. If I have to learn board level repair to get this thing going - then I will!

Thanks,

Chris

IBM_User
December 3rd, 2014, 07:23 AM
First thing would be to swap the X2 capacitor in the power supply.
I had recently a 5160 PSU on the workbench, after 5 mins mains was
plugged in it began to smoke.

It took several days to get that bad smelling smoke out of the room!

chjmartin2
December 4th, 2014, 06:57 AM
First thing would be to swap the X2 capacitor in the power supply.
I had recently a 5160 PSU on the workbench, after 5 mins mains was
plugged in it began to smoke.

It took several days to get that bad smelling smoke out of the room!

Good advice. Is there a battery in this sucker that I should worry about?

Timo W.
December 4th, 2014, 07:14 AM
There's normally no CMOS in an XT and hence no battery. But you never know, maybe it has a real-time clock added.

Stone
December 4th, 2014, 07:42 AM
I would just turn it on.

If it ain't broken, don't fix it!!!

modem7
December 4th, 2014, 12:26 PM
First thing would be to swap the X2 capacitor in the power supply.

Good advice.

I would just turn it on. If it ain't broken, don't fix it!!!
If it was known that the failure of a line suppression capacitor often caused secondary component failures (apart from a possible blown fuse), then I would be proactive, replacing all of the old line suppression capacitors in my power supplies. But I have never seen such a secondary failure.

Old Rifa made line suppression capacitors (picured at [here (http://www.minuszerodegrees.net/failure.htm)]) do have a 'bad reputation', which I have experienced many times, but many of my old power supplies have other brand/types of line suppression capacitors, and those have yet to fail. So I 'sit back and worry about it when it happens'. However, if I am in an old power supply (for whatever reason), that is when I take the opportunity to replace any (and there could be multiple) RIFA made line suppression capacitors.


Is there a battery in this sucker that I should worry about?
Some XT clones incorporated real-time clock (RTC) functionality into the motherboard, and that would include a battery somewhere.
Your XT clone may or may not have that.
If it doesn't, then it is possible that your XT clone has an expansion card that includes RTC functionality (along with a corresponding battery).

chjmartin2
December 6th, 2014, 05:00 AM
Hi,

So this Vendex Headstart Plus has an on-board battery, but I found a replacement. Unfortunately it is not the computer of my youth but a different Vendex. Interestingly enough, I can't find any reference material on the web for this machine. It is a Vendex Headstart Plus. It has two 5.25 floppy drives and a hard drive. It has a switch on the back that says "color/mono" and what looks like a CGA video port. I'm going to continue my search, but would appreciate any insight if anybody has some.

Chris

Denniske1976
December 6th, 2014, 07:34 AM
Sounds to me like indeed a CGA card, you could open it up and see if what card is there... My HeadStart LX-40 has an ATI CGA card, and interestingly this one also has the color/mono switch and even a GAME-port on the back and BUS-mouse port:

21707

chjmartin2
December 7th, 2014, 05:45 AM
Hi,

I am finding out this is a nice little machine.

It has a Faraday FE20-10A chipset. It is running a Fujitsu MBL8088-1 processer at what I believe is just under 10 Mhz. Is 10 Mhz the upper limit for 8088's? Can I (should I bother) replacing this with a V20? Anyway, I have to take it all the way apart before I plug it in. There appears to be some copper oxidation on some parts and I don't want to risk shorts. I am thinking about proactively replacing all of the caps on the board - but I always like to think - if it ain't broke don't fix it like I was told before. There is a battery so I have to get that one.

Oh and get this. I discovered that the Vendex Monitor and Keyboard I have already go with this PC not the one of my youth anyway. So I have a complete set. I am thinking maybe even retrobright.

Oh yeah - how do I max out RAM on this thing?

Chris

Robin4
December 7th, 2014, 05:54 PM
Is this computer an vendex headstart??

chjmartin2
December 10th, 2014, 10:24 AM
It is a Vendex Headstart Plus!

Robin4
December 11th, 2014, 07:23 PM
Do you have a picture of it? Really like to see it.

chjmartin2
December 14th, 2014, 06:38 AM
Hi,

This thread is as good a place as any. I would like to get this computer going, but got off to a hard start already. I have pictures below but the battery had clearly leaked, was metering out at .1V and so had to be removed. I have a new battery coming, but I know that I was having a hard time getting the old battery desoldered, so I ended up motion stressing them off to deal with the leftover bits later. Also, the power supply had 5 volts, but the 12 volt lines were pulling 4 volts as well, and the fan was turning slowly until I went ahead and gave it some percussive maintenance and then it "kicked it." 12V line barely hit 9. Tried it anyway, no luck. Got a new battery and a new power supply on the way. Here are the pics:

2180221798217992180021801

Chris

chjmartin2
December 14th, 2014, 06:44 AM
More pics:

2180321804218052180621807

chjmartin2
December 14th, 2014, 06:46 AM
218082180921810

chjmartin2
December 14th, 2014, 06:49 AM
http://bk0010.narod.ru/DRIVESPECS/MINISCRIBE/2704.txt.html

Stone
December 14th, 2014, 08:09 AM
The battery is not keeping the machine from booting.

The power supply may be good. If you test it correctly you can determine this.

Battery leakage is most often a major problem. You may find out that it is the only problem and the board is nonfunctional because of it.

Robin4
December 14th, 2014, 12:31 PM
Compliments to your system, i really like that machine.. Hope that you could restore it in its original condition..

Back in the days, my dad bought our first computer, the Vendex Headstart Explorer

http://www.vogons.org/viewtopic.php?t=30802

chjmartin2
December 14th, 2014, 01:03 PM
Hi,

So I removed the battery, it has 3 feet. I bought a replacement battery at 3.6V, but this one in nmh? (sorry, don't know the chemistry) Anyway, the grounding pad was corroded but that's it. I should be able to resolder in the new battery. The system won't function without a battery?

SpidersWeb
December 14th, 2014, 01:14 PM
Hi,

So I removed the battery, it has 3 feet. I bought a replacement battery at 3.6V, but this one in nmh? (sorry, don't know the chemistry) Anyway, the grounding pad was corroded but that's it. I should be able to resolder in the new battery. The system won't function without a battery?

The battery should not be required for normal operation.

I'd start with your power supply because a regulated supply should not vary in readings like that.

chjmartin2
December 20th, 2014, 05:38 AM
The battery should not be required for normal operation.

I'd start with your power supply because a regulated supply should not vary in readings like that.

Hi,

So I put in a power supply that metered out properly, and now the power led comes on but nothing else happens. The screen doesn't even flicker or change when I power it up. Any ideas where to start? I have removed the battery and did not yet replace it, so, should I be shorting where the battery was?

Chris

Stone
December 20th, 2014, 07:17 AM
Once again... if the battery leaked the board may have suffered major damage.

krebizfan
December 20th, 2014, 08:41 AM
Though the damage may not be exclusively near the battery. Basically, reseat everything to make sure no loose board or chip is keeping the system from starting. Then follow every trace on the motherboard and be prepared to solder in a wire to bridge any damage. The pictures look like a bunch of resistors (?) have been removed or broken behind the card slots. Confirm what they are and replace if necessary.

Could you provide a close up of the region directly under the battery? If the acid just ate an empty part of the board, repairs will be simpler than if power was routed to the slots through there.

chjmartin2
December 20th, 2014, 12:43 PM
Though the damage may not be exclusively near the battery. Basically, reseat everything to make sure no loose board or chip is keeping the system from starting. Then follow every trace on the motherboard and be prepared to solder in a wire to bridge any damage. The pictures look like a bunch of resistors (?) have been removed or broken behind the card slots. Confirm what they are and replace if necessary.

Does that mean desolder everything and redo it, or just reflow every connector on the back?



Could you provide a close up of the region directly under the battery? If the acid just ate an empty part of the board, repairs will be simpler than if power was routed to the slots through there.

It does not look like there are any messed up traces through there at all.

21853218542185521856

3pcedev
December 20th, 2014, 01:17 PM
Once again... if the battery leaked the board may have suffered major damage.

Notice how the serial,parallel and video ports on the back have turned green. It doesn't look like that is due to atmospheric corrosion; it's probably due to the battery electrolyte working its way along traces and exiting there. Also I am not sure if it is the photo but in your last picture some of the traces appear a bit darker / splotchy. That is a sign that they have been corroded under the soldermask.

T3 and T4 plus what looks like the Xtal (small silver barrel) all have green on their legs from the electrolyte. This can work its way into the plastic case and destroy the componants. Unfortunately I know this from experience.

The best way forward is to obtain/burn a supersoft ROM from here: http://www.minuszerodegrees.net/supersoft_landmark/Supersoft%20Landmark%20ROM.htm

If the computer will POST with this ROM it will at least narrow down the fault (it's possible you have bad RAM or some other unrelated fault). If it does not then I would start by replacing T3, T4, Xtal and anything else "easy" which has green or crusty white pins.

Stone
December 20th, 2014, 03:46 PM
If the acid just ate an empty part of the board....What acid??? This is not a car battery. The electrolyte is basic! :-)

Also, just because there is no visible trace damage there is the possibility of non-visible damage in the internal layers.

chjmartin2
December 20th, 2014, 03:52 PM
What acid??? This is not a car battery. The electrolyte is basic! :-)

Also, just because there is no visible trace damage there is the possibility of non-visible damage in the internal layers.

So, what you are saying is that it is a waste of time to try to salvage this board? That's really sad for me. Boo.

Caluser2000
December 20th, 2014, 04:00 PM
You may be able to bridge the traces with thin wire, even internal ones, if you can locate their beginning and end points. All depends how bad the damage is and how much time you want to spend on it. Schematics of the mobo, if available, would be invaluable.

3pcedev
December 20th, 2014, 04:59 PM
So, what you are saying is that it is a waste of time to try to salvage this board? That's really sad for me. Boo.

Not at all. Obtain a supersoft diagnostic rom (either burn your own or quite a few people here can post you one at cost) and give it a shot. As I said earlier there could still be a (very common) fault with the RAM which is preventing POST. The supersoft rom will tell you if this is the case and it only takes 5mins to try.

If that fails then try what I suggested above by replacing the easy things like those two transistors, crystal and capacitor which were near the battery. It will only cost a few dollars. You can try to search for open traces while you are at it; however without a motherboard schematic it is very difficult.

On the scale of 1-10 the (external) damage to your board is about a 3. It certainly could be a lot worse; for example if the battery leaked near the chipset IC's. Unfortunately there is no way to gauge the internal damage. There are no guarentees here, but saving the board is definitely worth a shot.

Stone
December 20th, 2014, 05:10 PM
So, what you are saying is that it is a waste of time to try to salvage this board? That's really sad for me. Boo.Not that it's a waste of time. But there's no guarantee that even by repairing everything that's visibly damaged will get the board to work again. There's always a chance for underlying, irreparable damage.

Robin4
December 20th, 2014, 05:19 PM
That motherboard is a proprietary one, special for that headstart case.. Throwing that board away, would be the same as throwing the whole systems away..
If he want that system running, he definitely needs to repair that board.. Really needs to reparing those bad traces on that board.

Caluser2000
December 20th, 2014, 05:31 PM
Probably unrelated but something else you could try is pulling the lead off the reset switch connector on the mobo if it has one. Had an issue with my XT clone which wouldn't boot because the switch was iffy.

krebizfan
December 20th, 2014, 05:45 PM
I posted previously in haste. I think the best next step is to closely examine the whole board. Determine what might need fixing, if it matters, and if it will be affordable from cost and time perspective.

1) No repair needed. The problem is something simple like chip not in its socket and simply plugging it back will permit booting. Having only pictures I will miss the things that can only be noticed in person.

2) Minor repairs in a small region. Worth trying and likely to work again.

3) Major board damage with lots of traces all surrounding the region. With a complete schematic, lots of work, and some luck, it might be possible to repair. But might never work again.

chjmartin2
December 27th, 2014, 07:21 AM
3) Major board damage with lots of traces all surrounding the region. With a complete schematic, lots of work, and some luck, it might be possible to repair. But might never work again.

There are not a lot of damaged traces but I can see dark regions when I look on the back. The part that is odd is that when I power it on the keyboard lights blink, the power LED from the motherboard is lot but I do not even get a flash from the CGA. I am going to try to burn that other BIOS but it seems that one is designed for IBM's. I think I have to meter continuity for every single trace because this PC either was in a flood or in a garage with moisture - unless the battery really went all of the place. (The 'pads' had green corrosion on them. I have it in my mind to do a high res scan on the board both sides. Remove all components, meter all traces, note which need wires to repair and go from there. How expensive is it to get a single board printed? Meaning - if I were to completely redraw the board (no idea how) and get a board reprinted (must be some type of prototyping service out there) would that set me back more than $500? Lastly - any ideas how I might find a schematic for this sucker? I doubt Samsung would help me...

modem7
December 27th, 2014, 12:04 PM
The part that is odd is that when I power it on the keyboard lights blink, ...
In most cases, that is a result of the keyboard receiving +5V and consequently doing a self test. The LEDs momentarily turning on is part of the keyboard's self test.

3pcedev
December 27th, 2014, 02:12 PM
I would say your motherboard is a 4 to 6 layer PCB. To even draw out the schematic by reverse engineering the current board will take (almost) forever, then you have to break up the schematic into layers and buses (data, ground, power etc). There are a lot of design considerations in this step to reduce noise and optimize the board area. Printing a board of that size with that many layers would be close to if not exceeding $500, plus many companies have a 3 board minimum.

Start by replacing the obviously damaged components and checking some obviously damaged traces as per my last post. It's cheap and will take you no time at all. It might be just that simple.

Also get a supersoft diagnostic rom. It will tell you if the whole board is bricked, or just part of it. Very useful tool (in this case).

arrow_runner
December 28th, 2014, 09:51 AM
I have one of these in rough condition that's been mostly stripped. The only internal parts left are the motherboard, keyboard controller and power supply. I'd sell the boards for cheap or if you want other reference pictures I can take some later.

chjmartin2
December 30th, 2014, 08:30 PM
I have one of these in rough condition that's been mostly stripped. The only internal parts left are the motherboard, keyboard controller and power supply. I'd sell the boards for cheap or if you want other reference pictures I can take some later.

I would take the MB! Maybe i can make 1+1=1. Any obvious corrosion on the MB? How much?

chjmartin2
January 1st, 2015, 07:29 AM
I have one of these in rough condition that's been mostly stripped. The only internal parts left are the motherboard, keyboard controller and power supply. I'd sell the boards for cheap or if you want other reference pictures I can take some later.

Arrow! I tried to respond to your PM but it says you have your PM queue maxed out and you can't receive any additional messages! :) If you could send me a PM with your email then we can move the convo over to that. My headstart plus only seems to have a mobo and not a separate CPU board - so not sure we are talking apples-to-apples here, but I am still interested.

chjmartin2
January 3rd, 2015, 12:43 PM
Hi,

So I removed the BIOS and ripped it to my hard drive. The image read fine. I removed the label on the BIOS chip and to my delight it had a window. I used my UV eraser and then burnt the 16K diagnostic BIOS onto the chip. I plugged it in and got nothing - again. This time though when I power off the computer I get an audible beep. Inside the instructions for the diagnostic ROM it told me to check some other stuff. (I got a Rigol DS1102E for Christmas which has already convinced me that I should have bought a proper scope years ago.) So this what I have done:

1. The power supply checks out and is getting from 5V, -5V and +12V everywhere.
2. The CPU MB8088-1 has 5V on Pin 20
3. The BIOS Chip TMS 27C128 has 5V on Pin 28
4. The CPU has a clock at 9.6 MHz. Image of the clock signal below.
5. I get low voltage on Pin 32 on the 8088 - but it look just like DC volt

22020

So my question is this - does this suggest that my 8088 CPU is no good or am I jumping to conclusions now?

Chris

chjmartin2
January 3rd, 2015, 02:44 PM
Hi,

So my question is this - does this suggest that my 8088 CPU is no good or am I jumping to conclusions now?

Chris

I have apparently decided to talk to myself. I have now looked closer that the CPU outputs and they appear to be doing something. I don't like that the "read" pin just seems to stay high all of the time. I also metered the CGA output pins and those are completely dead - like, nada. I tried to find information about the Paradise on-board PVC4 chip but can't find a datasheet for it, so I am at a loss as to how to meter it, but I'll just stab around and see if there is any signal there. Also I removed the 8088 CPU and then tested the clock chip again only this time it said the frequency was 4.7 Mhz instead of 9.6 Mhz, so with the CPU in the clock is 9.6 MHz and without it, the clock is at 4.7 Mhz. I have a Tandy 1000HX and I am wondering if I should just try that CPU in this one. I also went on line and grabbed a couple of CGA cards, but without knowing how to disable the on-board video that seems kind of useless too.

3pcedev
January 3rd, 2015, 02:51 PM
You could try an MDA card - they will work with the onboard CGA still in place. Not sure how the diagnostic ROM will handle this though - modem7 might have more of an idea.

modem7
January 3rd, 2015, 03:23 PM
You could try an MDA card - they will work with the onboard CGA still in place. Not sure how the diagnostic ROM will handle this though - modem7 might have more of an idea.
No idea, but nothing on the CGA output pins suggests that the SuperSoft diagnostics are not being run, and thus the diagnostics are not initialising the CGA circuitry.

When the 8008 is taken out of reset, it jumps to address FFFF0, which corresponds to an address very near the end the ROM. So, on the motherboard, the chip select logic for the ROM should be decoding that and producing a Chip Select signal to the 27C128. If you do not see that Chip Select, then the problem is very basic.


Also I removed the 8088 CPU and then tested the clock chip again only this time it said the frequency was 4.7 Mhz instead of 9.6 Mhz, so with the CPU in the clock is 9.6 MHz and without it, the clock is at 4.7 Mhz.
I do not know how exactly your DS1102E calculates frequency, but perhaps when the 8088 is in its socket (i.e. loading the clock generator), the resulting change in the clock waveform is such that it 'confuses' the 'frequency calculation' algorithm in your DS1102E.

Or, are you calculating the frequency manually by observing the waveform's period.

chjmartin2
January 3rd, 2015, 03:48 PM
When the 8008 is taken out of reset, it jumps to address FFFF0, which corresponds to an address very near the end the ROM. So, on the motherboard, the chip select logic for the ROM should be decoding that and producing a Chip Select signal to the 27C128. If you do not see that Chip Select, then the problem is very basic.

Ok, so I will watch pin 20 on the 27C128 (http://www.jaapsch.net/psion/pdffiles/Eprom016k_datasheet_27C128.pdf) and what should I look for? A fixed DC level or a spike/signal?




I do not know how exactly your DS1102E calculates frequency, but perhaps when the 8088 is in its socket (i.e. loading the clock generator), the resulting change in the clock waveform is such that it 'confuses' the 'frequency calculation' algorithm in your DS1102E.

Or, are you calculating the frequency manually by observing the waveform's period.

I am using the scope's calculator - yes it could be what you describe. I had guessed that maybe it was compatible with multiple frequencies and therefore I should try my Tandy 1000HX processor.

chjmartin2
January 3rd, 2015, 04:03 PM
Here is what I get when I scope Pin 20 on the 27C128 and then the output lines on the BIOS. It looks like an electron parade coming out of the output lines.

https://www.youtube.com/watch?v=TNoeOeSdM4A&list=UUbl7FbsvobOrgj3O-ray02A

modem7
January 3rd, 2015, 04:36 PM
Here is what I get when I scope Pin 20 on the 27C128 ...
The 27128 has two pins that both need to be taken low for the 27128 to generate an output, OE and CE. I have seen some engineers have the chip select signal going to both pins. Some instead will tie OE high and have the chip select signal going to CE. Some instead will tie CE high and have the chip select signal going to OE. This is where having the motherboard circuit diagram is useful.

So in the case of your motherboard, maybe it is the OE pin you need to monitor.

Whichever pin, it normally sits high, and will be taken low for the duration that the CPU is reading a byte from the 27128.


... and then the output lines on the BIOS. It looks like an electron parade coming out of the output lines.
The output pins of the ROM are connected to a data bus. A data bus is shared, so when you simply scope the data bus as you are doing, you are seeing the data bus output of many chips.

The fact that you are seeing data bus activity is a good sign.

Do you have a speaker connected to your motherboard? I ask, because the Supersoft diagnostics are known to produce error beeps. I am sure that someone recently had a faulty motherboard in which the Supersoft diagnostics produced error beeps, but no video.

chjmartin2
January 3rd, 2015, 05:02 PM
The 27128 has two pins that both need to be taken low for the 27128 to generate an output, OE and CE. I have seen some engineers have the chip select signal going to both pins. Some instead will tie OE high and have the chip select signal going to CE. Some instead will tie CE high and have the chip select signal going to OE. This is where having the motherboard circuit diagram is useful.

So in the case of your motherboard, maybe it is the OE pin you need to monitor.

Whichever pin, it normally sits high, and will be taken low for the duration that the CPU is reading a byte from the 27128.


The output pins of the ROM are connected to a data bus. A data bus is shared, so when you simply scope the data bus as you are doing, you are seeing the data bus output of many chips.

The fact that you are seeing data bus activity is a good sign.

Do you have a speaker connected to your motherboard? I ask, because the Supersoft diagnostics are known to produce error beeps. I am sure that someone recently had a faulty motherboard in which the Supersoft diagnostics produced error beeps, but no video.

I have a speaker connected but no keyboard although I could connect a keyboard. Before I put in the Supersoft ROM the computer produced no sound. Now that there is a Supersoft ROM installed when I turn off the computer I get an audible beep, but that is all it is. OH MY GOODNESS! I just went back to my workbench and plugged back in the speaker - I had it plugged in before, and then when I turned it on - I got beeps!!!!! Now I need to read what they mean... stay tuned.

chjmartin2
January 3rd, 2015, 05:24 PM
I have a speaker connected but no keyboard although I could connect a keyboard. Before I put in the Supersoft ROM the computer produced no sound. Now that there is a Supersoft ROM installed when I turn off the computer I get an audible beep, but that is all it is. OH MY GOODNESS! I just went back to my workbench and plugged back in the speaker - I had it plugged in before, and then when I turned it on - I got beeps!!!!! Now I need to read what they mean... stay tuned.

https://www.youtube.com/watch?v=eDAhArwKvVk

5 Long Hi Short Lows
9 Short Lows

chjmartin2
January 3rd, 2015, 05:29 PM
In the manual it says that means "can't initialize monitor."

modem7
January 3rd, 2015, 06:25 PM
In the manual it says that means "can't initialize monitor."
It means your video card.

I have a particular CGA card that the Supersoft dignostics produce a 'rubbish' display on, but the dignostics display fine on all of my remaining CGA cards.

If you have not already, try your CGA card in a different slot. Why? The battery leakage may have affected the contacts in that slot.

Does the CGA card itself appear okay, i.e. no apparent damage from the battery leakage, no blue/green 'gunk' on it?

And I read that your CGA card has a color/mono switch. Is that in the color position?

chjmartin2
January 3rd, 2015, 07:35 PM
It means your video card.

I have a particular CGA card that the Supersoft dignostics produce a 'rubbish' display on, but the dignostics display fine on all of my remaining CGA cards.

If you have not already, try your CGA card in a different slot. Why? The battery leakage may have affected the contacts in that slot.

Does the CGA card itself appear okay, i.e. no apparent damage from the battery leakage, no blue/green 'gunk' on it?

And I read that your CGA card has a color/mono switch. Is that in the color position?

CGA card is built into the motherboard. Paradise PVC4 is the IC involved. There seems to be a problem with the switch that controls Color/Mono as it didin't meter properly. I took out the switch so now I have to bridge the CGA color setting. Let me do some high resolution scans on the areas near the battery. Be right back to you...

chjmartin2
January 3rd, 2015, 08:47 PM
CGA card is built into the motherboard. Paradise PVC4 is the IC involved. There seems to be a problem with the switch that controls Color/Mono as it didin't meter properly. I took out the switch so now I have to bridge the CGA color setting. Let me do some high resolution scans on the areas near the battery. Be right back to you...

220282202922030

3pcedev
January 3rd, 2015, 10:15 PM
How did you go bridging out the switch?

chjmartin2
January 4th, 2015, 11:02 AM
How did you go bridging out the switch?

I just bridged where the connections would have been if the switch was set to Color.


So I examined every trace and metered out the connections and found two traces that needed to be fixed. I found other spots on the board where I bridged the traces. I now turn on the computer and get no audible beeps at all. I do get a beep when powering it off:

https://www.youtube.com/watch?v=iBEeWk1bUv4

Let's check the CGA signals:
https://www.youtube.com/watch?v=cXtoRYfHHEo

Let's try to run it... nope... but look, it now flickers the screen on shut down"
https://www.youtube.com/watch?v=qwbl-9bv1s8

I am going to check for bus activity again... but this is disappointing. I may have messed up because I routed past what looked like through holes in the board, and if it is a multi-layer PCB then there could be connections in the through holes. What I don't know is should I get a dremel and make a really small hole through the board and fill it with solder, or should I just try to scrap off as much as I can and pile the solder on there? Not sure what to do next...

chjmartin2
January 4th, 2015, 11:38 AM
And now there is no signal on the Bus like before at all. "Fixing" the traces doesn't seem to have had the intended effect.

chjmartin2
January 4th, 2015, 02:14 PM
I found more traces that looked damaged and fixed those as well. I plugged it back in and got an error code, but couldn't repeat that. Now really not sure what else to do....

modem7
January 4th, 2015, 05:11 PM
I plugged it back in and got an error code, but couldn't repeat that. Now really not sure what else to do....
A bad connection somewhere? I presume that you have reseated all socketed chips. Try powering on the motherboard multiple times, with the motherboard slightly flexed in a different way each time.

3pcedev
January 4th, 2015, 06:02 PM
The lack of beeping doesn't necessarily indicate a further fault.

It is possible that your repaired traces have 'fixed' whatever error the rom detected before. The ROM only beeps when an error is encountered; it will run completely silent if it does not find a fault. It's also worth mentioning the ROM isn't that brilliant at finding video card errors.

If the video card is no good then you wont see anything; nor will you hear anything. This has happened to me once before. I solved it by swapping cards but unfortunately you do not have the luxury.

There certainly could be problems with the via's / through holes that shift signals between layers. If there is a through hole (small one) that doesn't have a component it is definitely used to route between layers. Your best bet in repairing these would be to try to clean them as best you can then fill with solder from both sides. Don't be too shy holding the iron on the board; once you have wetted the joint with solder get it nice and hot by holding it on for 2 seconds or so. That will give you the best chance of success. I wouldn't go using the dremel; it will break the connection with the internal layers (if present).

chjmartin2
January 5th, 2015, 05:32 AM
The lack of beeping doesn't necessarily indicate a further fault.

It is possible that your repaired traces have 'fixed' whatever error the rom detected before. The ROM only beeps when an error is encountered; it will run completely silent if it does not find a fault. It's also worth mentioning the ROM isn't that brilliant at finding video card errors.

If the video card is no good then you wont see anything; nor will you hear anything. This has happened to me once before. I solved it by swapping cards but unfortunately you do not have the luxury.

There certainly could be problems with the via's / through holes that shift signals between layers. If there is a through hole (small one) that doesn't have a component it is definitely used to route between layers. Your best bet in repairing these would be to try to clean them as best you can then fill with solder from both sides. Don't be too shy holding the iron on the board; once you have wetted the joint with solder get it nice and hot by holding it on for 2 seconds or so. That will give you the best chance of success. I wouldn't go using the dremel; it will break the connection with the internal layers (if present).

I have a few CGA cards coming in. I really wish I could find the service manual/schematic/jumper settings for this motherboard. Are there any archives out there that I should be searching?

Scali
January 5th, 2015, 06:42 AM
CGA card is built into the motherboard. Paradise PVC4 is the IC involved.

This chip is also in my PC20-III I believe, and seems to be a close cousin to the ATi Small Wonder.
The chip is capable of running either in CGA mode (60 Hz) or in MDA/Hercules mode (50 Hz)... and even more awesome, it can be Hercules-compatible on CGA screens, and CGA-compatible on Hercules screens (without the need for SIMCGA.COM). The CGA color setting has nothing to do with that, if I'm not mistaken. It merely controls the composite output.
Are you getting a signal at all? It could be that you are getting an MDA/Hercules signal, which won't work on a CGA monitor. In that case you'd need to find where/how to switch it to CGA mode.
My Commodore PC20-III and ATi Small Wonder have 4 dipswitches for that. I believe that sw-2 is the one that switches between CGA and MDA/Hercules on both.

No idea if this info applies to your particular machine, and if it is of any use to you, but well, there it is :)

3pcedev
January 5th, 2015, 01:32 PM
I have a few CGA cards coming in. I really wish I could find the service manual/schematic/jumper settings for this motherboard. Are there any archives out there that I should be searching?

The problem with such old machines is that the internet was in it's infancy at the time. For anything 1995+ you have a chance at searching webpage archives like the wayback machine for the old manufacturers websites / peoples collection; which sometimes have interesting information.

There are a few archives for documentation; bitsavers and the internet archive are the main two I use. I had a look on both and unfortunately there is nothing under the heading of Vendex. There may not have even been a service manual released to the public for this particular machine. Finding IBM ones are easy as they were extremely popular at the time; same goes for the big clone companies like Vtech.

All you can really do is keep on trying to repair the board. Replace components near the battery with green legs (like those transistors); cross your fingers and you might get lucky.