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snq
July 28th, 2010, 07:33 PM
Thanks to the help I got here my 5170 is now up and running, so it was time to start with the 5160.

Its original power supply was dead and its contents have been replaced with a modified generic AT power supply - original wiring from the XT PSU hooked up to the inners of the newer PSU, a couple mounting brackets on the inside to mount the new contents, just by looking at it you wouldn't know the difference. Weight and noise wise - big difference!

Anyway, this machine is behaving quite weird. Wether or not it powers up seems to depend on what kind of stuff is attached to the mainboard. As soon as I attach the P8 connector to the mainboard, it will not power up. No disk spinning, the PSU fan doesn't start, nothing happens whatsoever. Without the P8, it works kind of fine :-? It will boot to floppy etc, everything seems fine. Until I put in a quadboard, then it's completely dead again. The same quadboard works fine in my AT.
I've tried removing everything from the system leaving just the mainboard with nothing connected to it (no keyboard, nothing) and it just will not power up when P8 is connected. With P8 disconnected, it's all fine again and I at least get a couple of beeps because nothing is connected.

Obviously the PSU is a bit of a hack, but I don't see why it wouldn't work. I don't think I'm the first person to replace it with something else. This PSU is rated at 145W, which should be plenty for an XT I think.
I've tested with another generic AT PSU with +5V on P8 removed, and that gives exactly the same result.

So I'm kind of looking for an explanation for why it's completely dead with P8 connected, and why it actually works in most cases with P8 disconnected. I wasn't exactly expecting it to do anything at all but I just had to test.

Chuck(G)
July 28th, 2010, 08:06 PM
Well, let's see, what does P8 carrry? Pins 6 and 5, ground Pin 4 -12 Pin 3 +12 Pin 2 NC (this must be blank Pin 1 Power Good

I assume with P8 disconnected, you've taken a voltmeter and checked the other leads. So, if the voltages are correct, then the motherboard probably has a short on it. You can quickly tell which of the remaining P8 connections is at fault by connecting only one at a time of the +12 and -12. (The PG pin shouldn't be able to take the system down, but if neither +12 or -12 connecting does, try it). Suppose you determine that the +12 causes a failure. You should trace the line and look for any shorted capacitors along the line. Note that the main board itself uses neither +12 nor -12, but routes them to the expansion connectors. However, there are decoupling capacitors on the motherboard. You can remove a suspect capacitor to test and replace it later.

snq
July 28th, 2010, 08:40 PM
Is the PG pin at all used on the XT? Because it doesn't seem to care that it's not getting anything there.
I have checked the leads they all give what they're supposed to give so I guess it's indeed the mainboard. I just checked by removing the 12V and -12V one at a time, and if either of them is connected (PG already removed since earlier testing), everything is dead. So right now I have a P8 connector with only 2 ground wires...
This sounds a little advanced for me, but I may just give it a shot.

Would the lack of +/-12V with P8 disconnected have any effect on the HD giving nothing but i/o errors? Because that would be the next thing that I need help with ;) No errors at POST and boots to floppy fine, but fdisk can't find a drive. Diskman sees 1 harddrive, controller tests okay, but any reading results in an error. Same thing with 3 different drives of which at least 2 are tested and working in my AT (those 2 are larger than 10M though and I have the controller that only supports 10). Tested different cables and different positions on them but everything else results in a 1701 error.

Chuck(G)
July 28th, 2010, 09:17 PM
The +12 is used on the XT hard disk controller; so it's not going to work if the supply isn't there.

Okay, put everything back into the P8 connector and remove all expansion cards. Does the unit power up? (i.e. we're trying to determine if it's a card or the main board)

snq
July 28th, 2010, 09:27 PM
I tested that earlier (removed all cards and disconnected everything else including drives and keyboard, and also tested with only the mainboard and a harddrive attached to put some load on the power supply) and it did not power up, not even the power supply fan spins. That's when I discovered that disconnecting the P8 connector made it somewhat work.
I guess I should be looking at either a new mainboard or see if I can repair this one, I don't have a lot of experience with that kind of repairs though... If anyone has a mainboard to spare I'm interested!

QuantumII
July 28th, 2010, 11:29 PM
Why not take a multimeter to the mainboard P8 connector to probe for shorts? (GND to +12v , GND to -12v)

Chuck(G)
July 29th, 2010, 07:40 AM
Why not take a multimeter to the mainboard P8 connector to probe for shorts? (GND to +12v , GND to -12v)

Yes, but the OP is unwilling to do board-level repairs.

I've said before that if you're going to get into this business of collecting antique technology, it's pretty much a good thing to learn how to repair it. Could you imagine an antique car collector who refused to get his hands dirty?

snq
July 29th, 2010, 08:00 AM
Actually there's some progress now, not sure if it actually helps me anything or if it just makes things worse.
I re-tested the empty system with the other PSU, and lo and behold, it started up with +12V connected. Not with -12V though. But I figured if I can get +12 that's better than nothing.
So I started putting the system back together, the plan was one card at a time and testing each time if it will power up. The first card to go in was the CGA card. That right away resulted in the system not powering up, however this time the PSU fan did spin. Some progress at least altho I obviously have no idea why it changed its behavior all of a sudden. If I disconnected P8 with only the CGA card in the system, it did power up.
I replaced the CGA card with an EGA card and changed the switches. Now it started up with P8 connected! So only -12V disconnected now, putting -12V back made it stop working again, so I think it's safe to say something is definitely wrong there but hopefully +12V is okay. I'm currently putting the system back together one card at a time. So far so good, the FDD controller is back and working (boots to floppy), and I just put the HDD controller and HD in and am about to check if maybe it will actually work now.

As for repairing the board, I'm not unwilling, in fact I'd love to be able to just repair it, but it's a steep learning curve for someone who never had to deal with anything like this before. Electronics are like wizardry to me... I don't even know how to go about for testing the capacitators for example. I'm sure all info is out there on the internet so it's just a matter of reading and learning. I guess I'm just afraid I'll break it even more, and in that case I would probably rather have a somewhat working system than a completely dead one. If we're going to use car analogies - I'd rather have a car without a stereo than a car that doesn't run at all because I ruined it while trying to fix the stereo.
And as for getting hands dirty, I do collect vintage snowmobiles and have a couple of old cars as well, and have no problem getting my hands dirty - most of the stuff I buy does need a lot of work ;)

Chuck(G)
July 29th, 2010, 08:14 AM
If you're worried about learning to solder and recognize components, the learning curve isn't that steep. And you have the benefit of the web, with instructional videos on YouTube and tons of print articles.

Otherwise, why bother with the old systems? Much newer machines are easier to find and will boot MS-DOS--and they run faster.

snq
July 29th, 2010, 08:58 AM
I'm mostly into this stuff for nostalgic reasons rather than becoming an electronics expert, and I'm sure I'm not the only one that is into this for that reason. But I can see that it'd be a good skill to have.
I know how to hold a soldering iron but as soon as anything more than just wires is involved, I freak out because I don't know what I'm doing ;)

The drives are still all giving me nothing but I/O errors so I guess I'm going to have to bite the bullet and see if I can fix this. Could obviously still be a bad controller, but the the power problem is quite obvious so that needs to be solved first because it's impossible to say anything about the rest of the system until this is solved. I know it will give me a lot of satisfaction if I do manage to get it all working without just replacing the mainboard!

Chuck(G)
July 29th, 2010, 12:50 PM
Well, if you ever get the desire, the +12 capacitors on the mainboard are C55 and C56; for the -12, they're C57 and C58.

snq
July 29th, 2010, 01:17 PM
So there's only 2 for each line? That wasn't as bad as I expected. I was kind of expecting having to de-solder half the board.
I was going to inspect the board visually but for whatever reason the floppydrive (in the left position) won't come out. Kind of gotta solve that first now...

snq
July 29th, 2010, 03:14 PM
Okay, the board is out and measuring between the -12V pin and ground gives none or very little resistance, so something is definitely wrong there. +12V to ground gives me a lot of resistance and it's a bit unstable, I think that is what it's supposed to do? I also measured the CGA card and it seems to have a short between +12V and ground, so I think that explains why replacing it with the EGA card made things a little better.
The C57/C58 capacitors don't show any external damage as far as I can tell, see attached pic.

How should I proceed from here? My idea was to remove the 2 capacitors one at a time and measure -12V to ground. If the resistance is okay I found the bad one?
I've been searching for a way to test them off the board, but I don't have a capacitor tester and measuring using a multimeter only seems to work with larger capacitors according to what I've been reading.

4159

Chuck(G)
July 29th, 2010, 04:00 PM
The "instablility" is probably due to a capacitor charging. The resistance should slowly increase as the capacitor charges.

Remove the -12 caps one at a time. Try the large one first--it's more likely to fail.

snq
July 29th, 2010, 04:59 PM
I had already gotten started before I read your reply.. So I started out with the smaller one, and that didn't help. But after removing the bigger 3 legged one, -12V to GND resistance was now infinite.
I really need to get myself one of those solder suckers, but I managed even if it took forever.

Problem found, I guess?
Now I just need to find something to replace it with.

Is there any proper way of testing these things with a regular digital multimeter? Or at least a test to see if they're completely broken or not?

Chuck(G)
July 29th, 2010, 05:04 PM
Capacitors are either good or bad--no in-between really. Since nothing is using your -12, go ahead and try powering the system up without it. You can always get another capacitor when you get around to needing it.

snq
July 29th, 2010, 05:30 PM
Are you sure the HDD controller isn't using -12V for something? Because that could explain the I/O errors.
All the other cards in there seemed to be doing their job just fine without the -12V though.

This wasn't so hard after all, so far anyway. Altho I wouldn't have been able to do it without the info you gave me, so thanks :)
I'm wondering how you knew C57/58 were the ones to look at, because I'd never have been able to figure that out by myself. Can't see any visible lines going from the -12V to there.

Chuck(G)
July 29th, 2010, 05:39 PM
Are you sure the HDD controller isn't using -12V for something? Because that could explain the I/O errors.
All the other cards in there seemed to be doing their job just fine without the -12V though.

No, the 5160 HDC is a bizarre little thing. It needs -5, but it gets it by using a DC-DC inverter to get the -5, not from the -5 line.


This wasn't so hard after all, so far anyway. Altho I wouldn't have been able to do it without the info you gave me, so thanks :)
I'm wondering how you knew C57/58 were the ones to look at, because I'd never have been able to figure that out by myself. Can't see any visible lines going from the -12V to there.

A schematic helps a lot. (http://www.retroarchive.org/dos/docs/ibm5160techref.pdf)

snq
July 29th, 2010, 08:03 PM
Okay, well I put everything back together for now with the -12V wire back in place, and it works like a charm now using either the modified XT PSU or the AT one with +5V disconnected from P8.

Unfortunately no improvement on the harddrive I/O problem, I'm afraid the controller is bad.

QuantumII
July 29th, 2010, 10:51 PM
Okay, well I put everything back together for now with the -12V wire back in place, and it works like a charm now using either the modified XT PSU or the AT one with +5V disconnected from P8.

Unfortunately no improvement on the harddrive I/O problem, I'm afraid the controller is bad.
There you go :-)
It could also be the HDD that is causing the I/O errors, not just the controller alone.

Chuck(G)
July 30th, 2010, 07:38 AM
I'm assuming that you've done a low-level format on the drive using this controller and the IBM setup/diagnostics disk for the 5160.

snq
July 30th, 2010, 08:11 AM
I haven't done a low level format on it yet. I was going to do a surface check using diskman first, but that gave me an error. Diskmans diagnosis tool passes the controller test, but not the seek test or any other test that checks more than just the controller.
I haven't checked if this drive (ST412) works on the 5170 yet though. I guess that would be a start as I know that that controller works. If not, I have other drives that work but no 10 MB ones. But as far as I understand they will work, but only the first 10 MB will be used?

The 5160 diagnosis disk tells me there is 1 fixed disk connected but I don't think it has any low level formatting options?

Chuck(G)
July 30th, 2010, 08:33 AM
You need the "advanced diagnostics disk", but you can also use Speedstor (http://members.dodo.com.au/~slappanel555/speedstor.htm) to do the same thing.

Remember that when it comes to RLL and MFM drives, each controller is sui generis--it understands its own low-level format and no others. You can't, for example, swap drives without low-level formatting between a 5170 and a 5160. Not at all like IDE or SCSI drives.

snq
July 30th, 2010, 09:21 AM
Is the XT advanced diagnostics disk available anywhere? I have the AT one but it doesn't work on the XT. If anyone has the files or an image that'd be great! I'll try Speedstor though.

Yea I know about each controller doing its own low level format but I figure it's a good way to see if the drive works at all.

aitotat
July 30th, 2010, 09:34 AM
Is the XT advanced diagnostics disk available anywhere?

It can be found here (http://www.ibm5150.net/software.html).

Chuck(G)
July 30th, 2010, 09:41 AM
Yea I know about each controller doing its own low level format but I figure it's a good way to see if the drive works at all.

I suspect that perhaps you don't understand what a low-level format does.

Until a drive is LL formatted, you have no idea if it's good or not. It's like trying to figure out if a blank CD-R is any good without writing to it.

snq
July 30th, 2010, 10:19 AM
I'm pretty sure I understand what it does - but then again, maybe I don't ;) I'll admit I've never had to deal with low level formatting before I got this 5160 and 5170.

Would a seek test in disk managers diagnostics program fail if the drive is not low level formatted first? And how about a surface check?

snq
July 30th, 2010, 11:17 AM
I wasn't able to get the diagnostics disk working, the machine either hangs or I get garbage on the screen. But Speedstor did the trick! :D

I think I may just have been using the wrong program all this time? Maybe my version of disk manager just doesn't support the XTs controller properly, or something. Speedstor did a surface scan without any complaints, and the drive is in good condition. It didn't find anything wrong at all but there was 1 bad spot on the label so I added it manually. I did have to add the quadboard because 256k was not enough to run the program.

Anyway, the drive is now partitioned and high level formatted, and the system boots to it just fine!

This is great, yesterday this machine was just a pile of parts and now it's a fully operating computer. Thanks for the help :!:

4174

Chuck(G)
July 30th, 2010, 01:01 PM
Happy to help. I assume that the next time I'm in your neighborhood, you'll buy me a beer?

snq
July 30th, 2010, 01:04 PM
Deal! Let me know when you're on your way ;)