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Vintage Computers Any vintage computer systems, calculators, video games etc., but with an emphasis on 1980s and earlier equipment.

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Old 27th Jan 2021, 10:53 pm   #281
ScottishColin
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Default Re: Non-working Commodore PET 3016

OK. I used the thin wire trick as advised above and we're all back in place.

I have exhaustively tested continuity from three places:

1) Underneath
2) top of board from the socket
3) top of board from the 6502 pins

All passes.

I think I'm a little further forward, but maybe only baby steps.

I now get a nice solid +5V on pins 40 and 8 - I wasn't on pin 8 before.

Frequency testing on the 6502 - quick testing gives me the following:
37 - 1mhz
39 - 1mhz
2 - no reading at all
7 - wobbles wildly between 2, 16, 17 & 18 Mhz
9 - no reading at all
10 - no reading at all
11 - no reading at all

Thanks all for the advice above re soldering/solder. Appreciate it.

Colin.
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Old 27th Jan 2021, 11:14 pm   #282
Mark1960
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Default Re: Non-working Commodore PET 3016

Hi Colin, could you try those same pins on the scope.

Also check pin 3, should be 1mhz.

Pin 2 should be held at Vcc, no frequency is correct.

Hopefully the scope shows something on 9, 10 and 11.

Pin 7 might be good news.
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Old 27th Jan 2021, 11:28 pm   #283
ScottishColin
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Default Re: Non-working Commodore PET 3016

Pin 3 shows 1Mhz

I'm not getting anything on 9/10/11 on my scope. No sine waves/square waves or frequency.

I can get pictures of the pins that did read something tomorrow if that helps.

Colin.
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Old 28th Jan 2021, 12:06 am   #284
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Default Re: Non-working Commodore PET 3016

Restoring the +5V supply to the CPU was a definite good outcome so that was worth it.

The activity on the SYNC pin (7) is interesting as it suggests the CPU is trying to execute instructions. As I understand it SYNC activates whenever the CPU thinks it is executing an instruction opcode, but not when it is fetching the information bytes which follow many opcodes. That would explain the erratic timing seen on SYNC, since some instructions have only a single byte, others have more.

However the lack of activity on A0-A1-A2 (9, 10, 11) is puzzling.

A few more pins for you to look at from a voltage / frequency / scope point of view.

Pin 4 (_IRQ)
Pin 6 (_NMI)
Pin 34 (R/W)
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Old 28th Jan 2021, 10:52 am   #285
ScottishColin
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Default Re: Non-working Commodore PET 3016

Voltages:

Pin 4 - 5.2
Pin 6 - 5.2
Pin 34 - 3.6

Frequencies to follow
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Old 28th Jan 2021, 11:12 am   #286
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Default Re: Non-working Commodore PET 3016

Scope testing here, using settings as per post 233 (noted in the document).

Not a lot to see here...

https://drive.google.com/file/d/13Zr...ew?usp=sharing
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Old 28th Jan 2021, 12:31 pm   #287
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Default Re: Non-working Commodore PET 3016

Don't know whether or not it's relevant but when I was probing my CPU's pins if I accidentally shorted two data/address pins the CPU would freeze and generate continuous highs or lows on all lines. It was then necessary to re-boot before proceeding with further measurements.

Alan
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Old 28th Jan 2021, 1:19 pm   #288
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Default Re: Non-working Commodore PET 3016

You might want to avoid shorting any two pins together, accidentally or otherwise.

High or mostly high on pins 4 and 6 are to be expected, pin 34 (r/w) I would expect to see some activity on, but mostly high. The voltage measurement of 3.6V there suggests that it is active, but spending more time high than low. However your scope trace seems to show it completely inactive.

Any activity on higher up address lines A3-A7? (12,13,14,15,16?).
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Old 28th Jan 2021, 1:52 pm   #289
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Default Re: Non-working Commodore PET 3016

Quote:
Originally Posted by SiriusHardware View Post
You might want to avoid shorting any two pins together, accidentally or otherwise.
Agreed but with the best will in the world it can happen when probing pins, albeit momentarily.

Alan
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Old 28th Jan 2021, 2:09 pm   #290
ScottishColin
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Default Re: Non-working Commodore PET 3016

Quote:
Originally Posted by SiriusHardware View Post
You might want to avoid shorting any two pins together, accidentally or otherwise.

High or mostly high on pins 4 and 6 are to be expected, pin 34 (r/w) I would expect to see some activity on, but mostly high. The voltage measurement of 3.6V there suggests that it is active, but spending more time high than low. However your scope trace seems to show it completely inactive.

Any activity on higher up address lines A3-A7? (12,13,14,15,16?).
No - no frequency reading on any of those pins.

They each read between 3.75 and 3.8V

Colin.
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Old 28th Jan 2021, 2:32 pm   #291
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Default Re: Non-working Commodore PET 3016

With the exception of the SYNC output the CPU is behaving almost as though the RDY input is asserted to put it into 'pause' mode but we know that RDY is high / inactive, as it is supposed to be.

Any ideas folks, before we have to suggest trying another CPU?
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Old 28th Jan 2021, 4:39 pm   #292
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Default Re: Non-working Commodore PET 3016

Is there any connection on the pcb to 6502 pins 5, 35 or 36?

Wondering if colin might have a later variant of 6502 remarked to the old nmos?
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Old 28th Jan 2021, 4:46 pm   #293
ScottishColin
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Default Re: Non-working Commodore PET 3016

Quote:
Originally Posted by Mark1960 View Post
Is there any connection on the pcb to 6502 pins 5, 35 or 36?

Wondering if colin might have a later variant of 6502 remarked to the old nmos?
Hi Mark - there are no tracks from pins 5, 35 or 36 on this motherboard. I attach a photo of the 6502 - looks original to me; happy to be corrected.

It's marked "MOS MPS 6502 3979"

Colin.
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Old 28th Jan 2021, 4:53 pm   #294
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Default Re: Non-working Commodore PET 3016

It also looks to be from the same stable as the 6522 IC next to it, so I would think both are original.
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Old 28th Jan 2021, 4:56 pm   #295
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Default Re: Non-working Commodore PET 3016

I'm confused regarding 6502 and 6502A processors - would this one work in the 3016? It says it will...

https://www.thefuturewas8bit.com/6502cpu.html
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Old 28th Jan 2021, 5:04 pm   #296
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Default Re: Non-working Commodore PET 3016

Quote:
Originally Posted by ScottishColin View Post
I'm confused regarding 6502 and 6502A processors - would this one work in the 3016? It says it will...

https://www.thefuturewas8bit.com/6502cpu.html
The 6502 had a rated 1MHz clock speed, the 6502A a 2MHz rated speed. Aside from that there are no significant difference so it should be fine.
Also TFW8b is a reputable supplier and know their business, I would trust them.
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Old 28th Jan 2021, 5:10 pm   #297
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Default Re: Non-working Commodore PET 3016

I'm confused about 6502 options too Colin but from what I've read the Rockwell 6502A should work in your 3016. Whether or not this is the best route for you to follow now I'll leave others to assess.

Alan
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Old 28th Jan 2021, 6:21 pm   #298
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Default Re: Non-working Commodore PET 3016

What should be the minimum pin connection set which is needed to make a 6502 free-run?

-5V supply (pin 8) - 5V
-0V supply (pins 1 and 21) - 0V
-Clock in (Pin 37) - 1MHz clock
-RDY (Pin 2) (Held high)
-IRQ (pin 4) (Held high)
-NMI (Pin 6) (Held high)
-Reset (Pin 40) (Momentarily low, then held high. The reset circuit takes care of that.)

Did I get everything? If so, then let's say you take a spare 40pin socket and you snip off all of the pins (-except- the ones above) flush with the underside of the socket. Really really close, so that there is no chance that the clipped pins will make contact with anything the socket is plugged into.

Plug the modified socket into the 6502 socket on the mainboard, then plug the 6502 into the modified socket and see if the 6502 will run, with the lower address lines active, with just those essential inputs connected. If it still doesn't wake up then I think we may have to consider that the 6502 is faulty, but if it does spring to life then we are looking for something which is preventing it from working when placed in the mainboard socket.

Rather than sacrifice a spare socket, you could achieve the same aim by gently bending out all the 'unwanted' 6502 pins to the side so they hang over the side of the mainboard socket, as you did with pin 7 of UG5 a while back. However this would be a lot more pins bent on a much more exotic IC, and there is always a risk that pins may snap when you try to bend them back into shape.

Before you consider trying this, just wait and see if anyone picks up anything I may have overlooked.
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Old 28th Jan 2021, 6:48 pm   #299
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Default Re: Non-working Commodore PET 3016

You might want to pull SO high (pin38) if only to stop it floating, as that is supposed to be a bad thing. I presume the board does this already.
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Old 28th Jan 2021, 7:01 pm   #300
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Default Re: Non-working Commodore PET 3016

I would recommend not plugging a turned pin socket into the turned pin socket soldered to the board. The pins on a turned pin socket are a bit larger diameter than an IC and can open up the contacts in the soldered socket a bit too much. I would only do this if a soldered turned pin socket has already loosened to the point of not holding the chip tightly, as a way to avoid replacing the soldered socket. As was already mentioned in earlier posts, replacing a turned pin socket is more difficult than the old/standard sockets, and the board has already had quite enough stress.

It probably is worth setting up the 6502 to run a nop test, but better to do it on a breadboard or protoboard

What I was thinking was to connect pin 36 to 5v, preferably through a resistor somewhere between 3k and 10k. Maybe link pin 36 to pin 2 is easier. This could be tried with a temporary link while watching pin 9 on the scope, if Colin has an extra hand to hold the scope probe

On later 65C02, I think including the rockwell, pin 36 was BE, bus enable.
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