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Bacon2002
April 1st, 2009, 11:06 AM
Hi,

I have just got hold of a PET 3008, I've fancied getting one for a while but it took sometime to find one.

Anyway, my problems are just starting as I can't get it to work but I have read a few stories about people on here bringing their PETs back from the brink and I was wondering if any of you guys could help me with mine.

When I turn it on I get a screen as follows:-

B*
PC IRQ SR AC XR YR SP
.; D387 E62E F0 C4 22 F5 F6
.

After some trial and error I have found that if I type "L" return it tried to load, load what I'm not sure.

Also "R" and "G" seem to do something?

I had a quick look inside and I have the following chips:-

UD3 blank
UD4 blank
UD5 blank
UD6 901465-01
UD7 901465-02
UD8 901447-24
UD9 901465-03

UF10 901447-10

Does anyone know what's up with my PET and can it be fixed.

Many thanks,

David

cosam
April 1st, 2009, 12:02 PM
Looks like it's booting straight into the machine code monitor. What happens if you press "x"? The ROMs all look correct for a BASIC 2 machine.

Bacon2002
April 1st, 2009, 12:06 PM
Hi,

Thanks for the super quick reply.

If I press "X" I get a repeat of the intial characters:-

PC IRQ SR AC XR YR SP
.; D387 E62E F0 C4 22 F5 F6
.X
PC IRQ SR AC XR YR SP
.; D387 E62E F0 C4 22 F5 F6
.

And so on until it goes off the screen.

Cheers,

David

cosam
April 1st, 2009, 12:20 PM
You get dropped to the monitor if something illegal gets executed, so my first guess would be that one of the ROMs is bad. Pressing "x" will usually exit back to BASIC but, as it was never running (properly) in the first place, you end up going back to the bogus code and the monitor pops up again. At least that's my theory ;-)

Have you tried reseating the ROMs? Any of them seem to be getting unusually warm? How about the RAM chips?

Bacon2002
April 1st, 2009, 12:52 PM
Cosam,

All the chips seem to be OK temperature wize the ROM Chips all run at about 30 deg C.

None of the smaller chips appeared to be especially hot.

One of the big chips at the top of the motherboard (the one second in from the Power supply) felt cold.

I pulled out and reseated all the ROM chips.

I have not reseated the big chips yet.

Thanks,

David

cosam
April 1st, 2009, 01:20 PM
One of the big chips at the top of the motherboard (the one second in from the Power supply) felt cold.
I think that's normal. If not, my PET is just as abnormal as yours ;-)


I have not reseated the big chips yet.
It's worth a try. A bad connection on the CPU (for example) could feasibly cause a problem like you're having.

Bacon2002
April 1st, 2009, 01:28 PM
cosam,

I'll get a small screwdriver and pull out the big chips in the morning.

If after reseated the chips the problem continues then is it possible to get replacement ROM chips or can the existing ones be re-programmed or am I just done for?

Or do you think it could be something else altogether?

Sorry for all the questions.

Thanks very much for your help it is very much appreciated.

Cheers,

David

cosam
April 1st, 2009, 01:42 PM
If after reseated the chips the problem continues then is it possible to get replacement ROM chips or can the existing ones be re-programmed or am I just done for?
The ROMs aren't of the programable variety, I'm afraid. You might be able to find a replacement set from a donor machine. Failing that you could shoehorn some modern EPROMs in. So all it not lost ;-)


Or do you think it could be something else altogether?
Certainly! This is all pretty much educated guesswork at the moment. If you can get hold of (or even just borrow) a set of ROMs easily I'd give it a whirl, but I wouldn't put money on it being the solution.

carlsson
April 1st, 2009, 02:22 PM
Probably one or more of the Basic ROMs that is faulty. If the CPU would not be OK, you would not even get the machine code monitor prompt. Eventually I could probably get you some (untested?) ROMs from scrap boards, but I don't know exactly how soon.

MikeS
April 1st, 2009, 04:43 PM
Where are ya?
And what kind of other computers do you have?

@Cosam/Anders: doesn't a 3008 use 'standard' pinout 2K/4K chips?

carlsson
April 1st, 2009, 10:07 PM
Possibly 2532 EPROMs (4K) are pin compatible, if you can get ahold of them as well as a programmer supporting them.

cosam
April 2nd, 2009, 12:48 AM
doesn't a 3008 use 'standard' pinout 2K/4K chips?
Heh - like the quotes ;-) All I remember is that the MOS parts aren't pin-compatible with the 27xx series. That's the great thing about standards - there are so many to choose from.

MikeS
April 2nd, 2009, 11:03 PM
Well, I think some of the ROMs are only 2K 2716s which are pretty standard, and it's not too hard to adapt a 2732 to a 2532-type socket if you have to...

The real trick is reading the contents to compare to known good ones if the system's not running; that's why I asked if by any chance there was another system with a compatible socket.

Bacon2002
April 6th, 2009, 10:36 AM
Hi,

I'm in Rayleigh in Essex and I have several PCs, I also have some PIC programmers, serial cable stuff, DMM, an osiloscope (although I'm not brilliant at using it), soldering equipment etc.

If it helps I have also got a lot of old home computer stuff like VIC20, C64, ZX81, Spectrum, BBC.

I took the PET's motherboard out to have a closer look, one of the IC's looks like it's been replaced it's a 74LS244 and is positioned at the front of the board.

It must have had a problem in the past as someone has scrapped/scratched several lines between the contacts on the back of the board between several of the IC's towards the front of the board.

Other than that it looks in good condition.

If anyone has or knows anywhere I can get any replacement IC's I would been very keen to discuss.

Or does anyone have any ideas what else I can try next?

Many thanks,

David

Bacon2002
April 6th, 2009, 10:44 AM
Hi,

Is this:-

http://www.elektor-electronics.co.uk/magazines/2000/december/2532-2732-eprom-adapter.56639.lynkx

the adapter you guys are referring to?

If so then where do you think I could get a 2732 EPROM and once I've got one what do I need to do with it?

Thanks,

David

carlsson
April 6th, 2009, 11:02 AM
You will need an EPROM programmer, or get a pre-programmed EPROM. 2732's are quite common both on eBay and among other collectors.

I have the following original ROMs in front of me, in case either of those would help you:

901465-01 = PET 3032 Basic
901465-02 = PET 3032 Basic
901465-03 = PET 3032 Kernel
901447-14 = PET 3032 Swedish Characters
901447-24 = PET 3032 Editor (Graphics keyboard) ??

These chips however are untested, and I can't really be bothered to pop open one of my working PETs to swap chips. If you like, I can send you some or all of those chips for postage costs, should be about 2 plus perhaps a few pennies to cover PayPal expenses. Please PM me if this sounds interesting.

Well, if they're pin compatible with 2532 perhaps I can use my EPROM programmer to read/dump them as 2532?

Bacon2002
April 6th, 2009, 11:13 AM
Carlsson,

That sounds great, those are mostly the same numbers as are in my machine.

I have sent a PM with my details, let me know if it doesn't arrive.

Fingers crossed, you never know those chips could solve my problem.

I'll keep you posted.

Thanks again,

David

cosam
April 6th, 2009, 11:49 AM
I took the PET's motherboard out to have a closer look, one of the IC's looks like it's been replaced it's a 74LS244 and is positioned at the front of the board.
Which one is it? There should be a letter/number combination next to it. These are used to buffer the data and address busses, so a fault here could indeed be your problem.


It must have had a problem in the past as someone has scrapped/scratched several lines between the contacts on the back of the board between several of the IC's towards the front of the board.
Do you have an ohm meter? It would be worth checking the pins of the IC are connected to what they ought to be. If not, reseat/resolder/repair as necessary.

cosam
April 6th, 2009, 11:52 AM
Is this:-

http://www.elektor-electronics.co.uk/magazines/2000/december/2532-2732-eprom-adapter.56639.lynkx

the adapter you guys are referring to?
I didn't check the pinouts but that's one way of doing it, yes. Another way is rolling your own out of an IC socket or two and a couple of wires.

carlsson
April 6th, 2009, 12:25 PM
The 74LS244 should be either UB3 or UC3. I'll send David the ROMs and let's hope it will make any improvement. Since the computer boots up but never starts Basic, I would think either 901465-01 or -02 is bad, unless the error is elsewhere on the board.

Bacon2002
April 6th, 2009, 12:27 PM
cosam,

The 74LS244 has the PCB ref "U111" in front of it.

I have not looked at any schematics but I did notice that a few of the pins on this 74LS244 appear (on the underside) to be soldered together. Is this correct?

(I have ordered a 74LS244, hopefully the correct type, just in case I needed to replace it.)

Yes I have a digital ohm meter, should I be looking to check that each of the IC pins are connected to the circuit board (checking for dry/broken joints) or should I be checking for something more complicated?

Thanks,

David

cosam
April 6th, 2009, 12:37 PM
The 74LS244 should be either UB3 or UC3.
If it's UB3, which buffers the top half of the address bus, that could be the problem right there.


I'll send David the ROMs and let's hope it will make any improvement. Since the computer boots up but never starts Basic, I would think either 901465-01 or -02 is bad, unless the error is elsewhere on the board.
Yep - going by the monitor output, I'd be guessing 901465-02 (as it's at 0xD000).

cosam
April 6th, 2009, 12:51 PM
The 74LS244 has the PCB ref "U111" in front of it.
Ah, that you be UI11 which buffers the RAM to the data bus.


I have not looked at any schematics but I did notice that a few of the pins on this 74LS244 appear (on the underside) to be soldered together. Is this correct?
Yes, the inputs and outputs are "doubled up" as it were.


Yes I have a digital ohm meter, should I be looking to check that each of the IC pins are connected to the circuit board (checking for dry/broken joints) or should I be checking for something more complicated?
Seeing as this chip is on the data bus, which would appear to be working OK, I don't think it's the problem. If you still want to check, ideally you'd measure from the actual pin on the IC to a pin on another component it connects to. If you get no continuity or measure any significant resistance, you can zero in on the problem area by checking at other points along the path. Schematics are here (http://zimmers.net/anonftp/pub/cbm/schematics/computers/pet/2001N/index.html).

Bacon2002
April 6th, 2009, 12:56 PM
Hi,

The UB3 and UC3 74LS244's appear to be (visually) original and are at the other end to the UI11 74LS244.

It looks like when I was referring to the front I should have said something like at the keyboard end.

David

cosam
April 6th, 2009, 01:06 PM
The UB3 and UC3 74LS244's appear to be (visually) original and are at the other end to the UI11 74LS244.

It looks like when I was referring to the front I should have said something like at the keyboard end.
Heh - no, my bad. I had a quick glance over my own board here and overlooked those two '244s at what I'd also call the front ;-)

carlsson
April 6th, 2009, 01:09 PM
This is how my board looks on the bottom side:
1592

Bacon2002
April 6th, 2009, 01:20 PM
Carlsson,

It's difficult to tell from the photo which of the pins are connected together within the PCB.

Tomorrow morning I'll dig out my camera and take some pictures of the PET, it's PCB and this IC from the underside.

Thanks for all your help guys.

David

carlsson
April 6th, 2009, 01:45 PM
Well, if they're pin compatible with 2532 perhaps I can use my EPROM programmer to read/dump them as 2532?
Great thinking. I configured the programmer for TI 2532 chips and successfully read all four ROMs. Then I set up WinVICE to use these ROM dumps instead of the default ones, and it works like a charm. I believe the dumps even are identical to the 3032 ROM set included with the emulator.

It means my ROM chips are fine, so if changing David's ones with this set doesn't fix his PET, something else is at fault. Perhaps a rusty ROM socket?

Bacon2002
April 7th, 2009, 02:02 AM
Carlsson,

Thats great news that the chips function correctly.

Here are some pictures of the PET:-

http://www.vintage-computer.com/vcforum/attachment.php?attachmentid=1595&stc=1&d=1239098379

Screen:-

http://www.vintage-computer.com/vcforum/attachment.php?attachmentid=1596&stc=1&d=1239098379

74LS244 - Underside of UI11 and UI10

http://www.vintage-computer.com/vcforum/attachment.php?attachmentid=1597&stc=1&d=1239098379

I'll post some more of the motherboard and the ROM chips etc.

Thanks,

David

cosam
April 7th, 2009, 02:18 AM
74LS244 - Underside of UI11 and UI10
That looks correct. The pins connected to each other on UI11 should follow the same pattern as UI10, i.e. four pairs on each side, which they do. I suspect it's just more noticeable on UI11 as it is hand-soldered and maybe some solder mask has been scraped off between the pins. But anyway - if there was a problem here the symptoms would be a lot worse: blank or garbage screen and definitely no monitor running.

Hopefully carlsson's (now proven good) ROMs will get you running again.

Bacon2002
April 7th, 2009, 02:19 AM
Here are some pictures of the Motherboard and ICs:-

Mainboard

http://www.vintage-computer.com/vcforum/attachment.php?attachmentid=1598&stc=1&d=1239099408

ROMs

http://www.vintage-computer.com/vcforum/attachment.php?attachmentid=1599&stc=1&d=1239099408


http://www.vintage-computer.com/vcforum/attachment.php?attachmentid=1600&stc=1&d=1239099408


http://www.vintage-computer.com/vcforum/attachment.php?attachmentid=1601&stc=1&d=1239099408


http://www.vintage-computer.com/vcforum/attachment.php?attachmentid=1602&stc=1&d=1239099408

Bacon2002
April 11th, 2009, 02:42 AM
Carlsson and Cosam,

http://www.vintage-computer.com/vcforum/attachment.php?attachmentid=1627&stc=1&d=1239446201

http://www.vintage-computer.com/vcforum/attachment.php?attachmentid=1628&stc=1&d=1239446201

I'm over the moon........

Many, many thanks for all your help, special thanks to Carlsson for the ROMs, without which my PET would be just a large and, of course, cool looking paper weight.

Cheers guys,

David

cosam
April 11th, 2009, 02:51 AM
Good to see you're up and running again! Which ROM was it in the end?

carlsson
April 11th, 2009, 03:16 AM
Ah, you do have 32K memory on that PET so it is upgraded from a 3008 to a 3032.

Bacon2002
April 11th, 2009, 04:07 AM
Hi,

I think it was the 901465-02 ROM.

The good news keeps getting better, in all the excitement I didn't notice the 31743 bytes free.

Brilliant....


Ta,

David

carlsson
April 11th, 2009, 05:04 AM
If you can identify your 901465-03 (Kernel) is fine, perhaps you can send it further to our German friend track18 who just figured his is bad? Both are 30xx machines so the ROMs should be identical.