Commodore PET 2001 voltage regulators

[retromit]

Originally Posted by SiriusHardware

Mysterious though, wasn't it, the way the IEEE buffers appeared to be working and only just this minute suddenly decided not to? As you've said yourself, never let a PET know that you think you have fixed it.

The best theory I can come up with is that the mere process of running the test, which excercises all the buffers in the chips, made a buffer which was about to fail anyway, fail. This was a discovery which needed to be made and fixed, though, before attempting to connect something like an SD2PET to the port.

I must admit, I did wonder what could have happened after the successful POKE/PEEks run only a few days earlier - which is why I thinking that perhaps flexing the motherboard a little for the processor change/6520s had caused this. However, your theory (and that of Slothie) could be a more plausible explanation. The PET was probably switched on for the longest since I had it when I was typing in the IEEE test code. It could have been the code running, or just the IC warming up and then failing.

As you say, it was a problem to be found and pleased we have. I just hope there are no more gremlins hiding away when this is (hopefully) fixed!

Tim.

[SiriusHardware]

Well...

Have you had a look at that shift key yet?

[ajgriff]

Originally Posted by Slothie

It could have been as simple as a cracked bond wire or similar, that worked (just) until the machine was powered up for long enough to warm the chip. expand the die and open up the gap. Unfortunately equipment stored for a long while can often work for a while and then deterioration of many years, or moisture ingress can put the final straw on the camel's back, so to speak.

I think the damp theory holds water (sorry!). I've just been looking again at Colin's photos which clearly show that his PET had been in a damp evironment for a very long time. It's even possible that water got inside the case. This might help to explain the remarkable number of failed chips. Also interesting that the socketed (raised above a shallow accumulation of water?) chips seemed to have survived better. This contrasts with my own PET which had been in dry storage where 6 of the 8 chip failures were down to the unreliable 6550 RAM chips.

Alan

[retromit]

I've been getting ready for the new IC to arrive, so there's now a socket for UA7. Just to make sure all was okay, I've reinserted the original chip and the voltages reflect what I originally recorded; plus the IEEE test code still reports the pin 7 issue. So at least it's consistent and I'm happy the socket seems to be okay.

So I should now be ready for when the new IC arrives.

[SiriusHardware]

While Colin's machine certainly had been in an almost fatally damp environment I haven't had much of a sense that that was the case with Tim's, except for the fact that his UD5 PROM had a couple of pins nearly corroded off.

There was a recent thread somewhere else about plastic vs. ceramic IC packages and how plastic ones were more prone to water absorption, or something along those lines. I can't remember where that was.

[retromit]

Originally Posted by SiriusHardware

Well...

Have you had a look at that shift key yet?

I've been meaning to mention this and the shift key is now working. After viewing the video Colin posted I was going to get ready to remove the keyboard. However, I just thought I'd give the key a few, repeated presses and it eventually sprang into life! Again, it seems like I have been quite fortunate with the keyboard, especially after reading about Colin's issues with his (and others I've read/seen). As it stands, all the keys work, and they certainly had a good workout for the inputting of the IEEE code.

Tim.

[retromit]

Originally Posted by SiriusHardware

While Colin's machine certainly had been in an almost fatally damp environment I haven't had much of a sense that that was the case with Tim's, except for the fact that his UD5 PROM had a couple of pins nearly corroded off.

There was a recent thread somewhere else about plastic vs. ceramic IC packages and how plastic ones were more prone to water absorption, or something along those lines. I can't remember where that was.

When I bought the PET from the original owner, he stated that it had just been left in the loft for quite a number of years. There are a few small patches of rust just breaking out on the top of the case and monitor, but it was mainly just very dusty inside when I first viewed it. I didn't really see any potential water damage.

A few of the ICs do seem to have darker pins, but the UD5 PROM was the worse; it lost one leg and a couple more were very loose.

Talking of PROMs, that's really good news about the Hitachi EPROMs you bought from eBay and were able to program.

Tim.

[SiriusHardware]

there's now a socket for UA7

Well done getting UA7 out intact, although I shouldn't be surprised because you also desoldered that 6502 you were using in the PET from the VIC-20, I think? A smaller IC would be no problem for you if you can take a 40-pinner out of a double sided PCB without causing damage.

At least that will allow you to prove, definitely, that UA7 was faulty once you have a replacement.

-Put new UA7 in - fault goes away.
-Put original UA7 in - fault comes back.

Or that's how I see it going, anyway. It's always nice to be able to show that a device you replaced was definitely faulty.

[retromit]

Originally Posted by SiriusHardware

Well done getting UA7 out intact, although I shouldn't be surprised because you also desoldered that 6502 you were using in the PET from the VIC-20, I think? A smaller IC would be no problem for you if you can take a 40-pinner out of a double sided PCB without causing damage.

At least that will allow you to prove, definitely, that UA7 was faulty once you have a replacement.

-Put new UA7 in - fault goes away.
-Put original UA7 in - fault comes back.

Or that's how I see it going, anyway. It's always nice to be able to show that a device you replaced was definitely faulty.

Yes, the desoldering station makes good work of it! I followed a similar process for the VIC with regards to the processor; just soldered in a socket, then inserted the 6502 from the PET. The VIC just returned a black screen; put the original VIC 6502 in, the VIC is happy.

It's really useful having the two test POKE/PEEKs, as well as the IEEE test code. I think with those, and being able to switch the ICs, we'll have a definite answer.

Tim.

[ajgriff]

Originally Posted by SiriusHardware

While Colin's machine certainly had been in an almost fatally damp environment I haven't had much of a sense that that was the case with Tim's, except for the fact that his UD5 PROM had a couple of pins nearly corroded off.

There was a recent thread somewhere else about plastic vs. ceramic IC packages and how plastic ones were more prone to water absorption, or something along those lines. I can't remember where that was.

Yes although lofts often suffer sharp temperature changes which can occasionally cause condensation, thus the small patches of rust. In any event, aside from the one ROM, Tim's machine has only exhibited two chip failures (so far!). This is in sharp contrast to the seventeen failures in Colin's damp PET.

I can't find the ceramic package post/thread either but ceramic chips generally seem to have a better reputation for longevity than their plastic bretheren.

Good news with the shift key Tim.

Alan

[Slothie]

Originally Posted by ajgriff

I can't find the ceramic package post/thread either but ceramic chips generally seem to have a better reputation for longevity than their plastic bretheren.

Alan

"Mil spec" chips (like 54 series logic) were usually ceramic, probably for this reason.

[SiriusHardware]

good news about the Hitachi EPROMs you bought from eBay

Yep, I guess on that basis they are 'safe' for other people to order. The final price for the four, with carriage added, was a fraction under £11.00, so call it £2.75 each. Still not a bad price.

I believe they will directly replace UD5 (The BASIC Toolkit), UD6, UD7 and UD9.

UD8 is a bit of a special case because it is a 2K device which must only be enabled when the address is E000-E7FF. The peripheral ICs (VIAs, etc) are mapped into the E800-E8FF range.

If you were to put a 2532 in there it would be enabled whether A11 (pin 18) was high or low and would clash with the peripheral ICs. On the original UD8 PROM device, pin 18 is 'CS2' which is an active-low enable, so the original chip is only enabled when A11 is low.

By pure luck rather than design you can put a 2716 in UD8 position and the way the pins fall, with 2716 CE landing on the socket's A11, it will work, so UD8 would need to be a 2716. Or ...

You could also use a 2732 (not 2532) as UD8 - if a 2732 was inserted in UD8 position then pin 21 (its A11 pin) would be held permanently high - therefore the code would need to be programmed into the upper half of the device, but as long as that was done, it should work.

[retromit]

Hi. Just thought I'd give a quick update. The ICs from Cricklewood Electornics arrived today, so the replacement UA7 was put in place. The voltages (after running the POKE) on pins 9, 11, 13, 15 were all identical, and the two POKE/PEEK commands both returned the correct values.

I then loaded the IEEE code, and it looks like all is well after running it. I left the code just looping for 1 hour 30 minutes, and each pass went through successfully.

So it looks like the replacement chip is all good, and the IEEE seems a lot happier!

Just want to say many thanks once again for all the help and support provided. It really has been appreciated.

Tim.

[ajgriff]

Alan

[Timbucus]

well done another fully restored PET

[ajgriff]

Originally Posted by retromit

Yes, the desoldering station makes good work of it! I followed a similar process for the VIC with regards to the processor; just soldered in a socket, then inserted the 6502 from the PET.

Completely off topic but as someone who has, at times, struggled with desoldering equipment I'd be interested to know the make and model of your desoldering station as you clearly get on well with it.

Alan

[retromit]

Originally Posted by ajgriff

Completely off topic but as someone who has, at times, struggled with desoldering equipment I'd be interested to know the make and model of your desoldering station as you clearly get on well with it.

Alan

I bought this one from CPC:

https://cpc.farnell.com/duratool/d00...P=TREML007-005

I’ve found it to be really good, providing it’s cleaned after each use. I just add a small amount of new solder to the pins when using it, and it really seems to help get the old solder out cleanly.

Tim.

[retromit]

Originally Posted by Timbucus

well done another fully restored PET

Thanks. Fingers crossed nothing else crops up, but I’ll keep running the tests for now to make sure it still seems happy.

Tim.

[ajgriff]

Originally Posted by retromit

I bought this one from CPC:

https://cpc.farnell.com/duratool/d00...P=TREML007-005

I’ve found it to be really good, providing it’s cleaned after each use. I just add a small amount of new solder to the pins when using it, and it really seems to help get the old solder out cleanly.

Thanks Tim. Looks like a good piece of kit.

Don't push your luck too far with the PET or it'll throw another wobbly! Seriously though mine's behaved impeccably since its return to full health earlier this year. I'm even considering giving it an SD2PET for Christmas.

Alan

[retromit]

Originally Posted by ajgriff

Thanks Tim. Looks like a good piece of kit.

Don't push your luck too far with the PET or it'll throw another wobbly! Seriously though mine's behaved impeccably since its return to full health earlier this year. I'm even considering giving it an SD2PET for Christmas.

Alan

I’ve had no problems with the desoldering station, Alan. It’s been a useful piece of kit. There are a few YouTube videos out there of people using it, so could be helpful.

I know what you mean about pushing my luck! I’m just pleased to have it all working now. I’m also looking at the SD2PET as well. It looks a good piece of equipment . I think I’ll also have to start looking at cleaning up the case/keyboard as well; there are a couple of light rust marks, so this could be the next job.

Tim.