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Old 10th Apr 2021, 9:23 pm   #1541
ortek_service
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Default Re: Non-working Commodore PET 3016

Quote:
Originally Posted by SiriusHardware View Post
Quote:
Which unfortunately is open-Collector
I missed that little detail

Last time we ran into this problem the OP didn't have a scope so we never got as far as trying to analyse the problem, we just went for a chip change which fortunately did solve it.
I did have to check the datasheet, as I had a feeling it would be when I saw the outputs were all inverted (But forgot it was TTL so now corrected Drain to Collector!)

However, if it's inputs are changing correctly then I can't see there could be anything else to explain the incrementing by 2 fault symptoms
- as I did check that it wasn't just 2 of the 10 row scan lines that could be shorted together (Although you could be really unlucky at have 5 shorts between adjacent pairs)

But we do know how fond this PET (Although technically a CBM model?) seems to be of devouring TTL IC's.......
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Old 10th Apr 2021, 10:41 pm   #1542
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Default Re: Non-working Commodore PET 3016

I have ordered a new 74LS145 which I guess will arrive Tuesday.

I will resolder the broken trace tomorrow and retest continuity.

I am assuming the 74LS145 is UC9 - is that right?

Colin.
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Old 10th Apr 2021, 10:50 pm   #1543
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Default Re: Non-working Commodore PET 3016

Quote:
I am assuming the 74LS145 is UC9 - is that right?
Indeed so.
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Old 10th Apr 2021, 10:51 pm   #1544
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Default Re: Non-working Commodore PET 3016

Thanks.

Feel free to take tomorrow off...

Colin.

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Quote:
I am assuming the 74LS145 is UC9 - is that right?
Indeed so.
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Old 10th Apr 2021, 10:56 pm   #1545
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Default Re: Non-working Commodore PET 3016

There's still a chance that the UC9 (74LS145) is actually OK, and you could confirm this if you want before changing it / waiting for it to arrive, if order has been completed - See below, from previous post, for what to check:


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>>
>>

So it does rather look like an issue with bit0 of the BCD code on the 74LS145 is not working. And there's still a chance of a bad connection to the 6520 PIA (or even that itself to be a 'bit' dodgy!)

Probing the 'KEYA' line at:
UC9(74LS145) Pin 15 ('A' input) /
UC7(6520) Pin 2 (PA0)

should hopefully see if that is switching OK at both ends and therefore working OK at least - before suspecting/condemning the 74LS145

>>
>>
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Old 10th Apr 2021, 11:00 pm   #1546
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Default Re: Non-working Commodore PET 3016

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Originally Posted by ScottishColin View Post
I have ordered a new 74LS145 which I guess will arrive Tuesday.

I will resolder the broken trace tomorrow and retest continuity.

I am assuming the 74LS145 is UC9 - is that right?

Colin.
Check for activity on the A input first, UC9-15.

Would be a shame to wait until Tuesday to find it was the lack of input that caused the problem.
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Old 10th Apr 2021, 11:22 pm   #1547
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Default Re: Non-working Commodore PET 3016

Does there need to be keyboard activity during these tests?

Colin.


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Originally Posted by SiriusHardware View Post
Expanding on Julie's thoughts in #1535 I suggest this, only when that track fault has been fixed.

----

Scope UC7 pins 2, 3, 4, 5

Scope UC9 pins 15, 14, 13, 12 - should have the same waveforms on as the above.

Then scope the following pairs of pins together, always with the first pin of each pair on the upper trace.

UC9 pins
1 and 2
2 and 3
3 and 4
4 and 5
5 and 6
6 and 7
7 and 8
8 and 9
9 and 10
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Old 11th Apr 2021, 12:37 am   #1548
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Default Re: Non-working Commodore PET 3016

No pressing of keys is required, as just need to test the control of the keyboard rows-scanning outputs, that is done by the Kernal ROM
- So need that one in place, and it booted into BASIC's normal operation.

However, you only really need to probe 1 or 2 pins, as it's been possible from the fault symptoms to narrow this down to the least-significant bit of the 4 BCD lines into the UC9 74LS145.

So only really need to (as suggested in the 2 posts prior to the previous one):

Probe the 'KEYA' line at: UC9 (74LS145) Pin 15 ('A' input)
& (particularly if no activity there) also: UC7 (6520) Pin 2 (PA0)
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Old 11th Apr 2021, 7:51 am   #1549
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Default Re: Non-working Commodore PET 3016

I'd better point out that these measurements, as Owen pointed out, won't work unless some resistors are added - so don't bother with those at the moment.

Code:
UC9 pins
1 and 2
2 and 3
3 and 4
4 and 5
5 and 6
6 and 7
7 and 8
8 and 9
9 and 10
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Old 11th Apr 2021, 8:11 am   #1550
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Default Re: Non-working Commodore PET 3016

If you get desperate to do those measurements, each of the pins of UC9 under test will need one end of a 10K resistor connected to it; with the other end connected to UC9 pin 16 or any other convenient +5V pin.

Also, I think UC9 pin 8 is actually 0V; so the last three tests probably should be comparing pins 7 and 9, pins 9 and 10 and pins 10 and 11 respectively.
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Old 11th Apr 2021, 12:06 pm   #1551
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Default Re: Non-working Commodore PET 3016

OK - that's done and continuity is restored. Thanks to all who suggested it.

I need to steal some clear lacquer now to cover it over.

Colin.


Quote:
Originally Posted by Mark1960 View Post
Quote:
Originally Posted by ScottishColin View Post
Are there good ways to deal with these kind of issues?
I think for that trace you can scrape about 3mm of track clear of solder resist at each end of the break and use a single strand from a multistrand cable to link the two ends. Keep the solder to a minimum and it should still allow the keyboard to be reassembled.

Edit: Is three a record for cross posting?
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Old 11th Apr 2021, 4:23 pm   #1552
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Default Re: Non-working Commodore PET 3016

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Originally Posted by ScottishColin View Post
OK - that's done and continuity is restored. Thanks to all who suggested it.

I need to steal some clear lacquer now to cover it over.
Most pound stores will have clear nail polish in their cosmetics sections. (Bloke tip: it probably will be near one end or the other, may be labelled "base coat" or "top coat" and probably will have a white lid.)
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Old 11th Apr 2021, 4:34 pm   #1553
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Default Re: Non-working Commodore PET 3016

Two screenshots attached.

Colin.


Quote:
Originally Posted by ortek_service View Post
No pressing of keys is required, as just need to test the control of the keyboard rows-scanning outputs, that is done by the Kernal ROM
- So need that one in place, and it booted into BASIC's normal operation.

However, you only really need to probe 1 or 2 pins, as it's been possible from the fault symptoms to narrow this down to the least-significant bit of the 4 BCD lines into the UC9 74LS145.

So only really need to (as suggested in the 2 posts prior to the previous one):

Probe the 'KEYA' line at: UC9 (74LS145) Pin 15 ('A' input)
& (particularly if no activity there) also: UC7 (6520) Pin 2 (PA0)
Attached Thumbnails
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Name:	UC9 pin 15 - 20210411.jpg
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ID:	231493   Click image for larger version

Name:	UC7 pin 2 - 20210411.jpg
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Size:	44.3 KB
ID:	231494  
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Old 11th Apr 2021, 4:35 pm   #1554
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Default Re: Non-working Commodore PET 3016

I managed to borrow some from my better half ta. Tip noted though.

Colin.


Quote:
Originally Posted by julie_m View Post
Quote:
Originally Posted by ScottishColin View Post
OK - that's done and continuity is restored. Thanks to all who suggested it.

I need to steal some clear lacquer now to cover it over.
Most pound stores will have clear nail polish in their cosmetics sections. (Bloke tip: it probably will be near one end or the other, may be labelled "base coat" or "top coat" and probably will have a white lid.)
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Old 11th Apr 2021, 4:37 pm   #1555
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Default Re: Non-working Commodore PET 3016

Hopefully this doesn't make any difference - the ShiftLock key has been desoldered (it's a different type of key to all the others) and the two wires are just floating apart from each other and not touching anything right now.

Colin.
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Old 11th Apr 2021, 4:38 pm   #1556
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Default Re: Non-working Commodore PET 3016

I've scoped UC9/15 and UC7/2 as per a later suggestion.

Would it still be useful for me to test the other UC7 (3, 4 and 5) and UC9 (12, 13 and 14) pins?

Colin.


Quote:
Originally Posted by SiriusHardware View Post
Expanding on Julie's thoughts in #1535 I suggest this, only when that track fault has been fixed.

----

Scope UC7 pins 2, 3, 4, 5

Scope UC9 pins 15, 14, 13, 12 - should have the same waveforms on as the above.

Then scope the following pairs of pins together, always with the first pin of each pair on the upper trace.

UC9 pins
1 and 2
2 and 3
3 and 4
4 and 5
5 and 6
6 and 7
7 and 8
8 and 9
9 and 10
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Old 11th Apr 2021, 4:52 pm   #1557
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Default Re: Non-working Commodore PET 3016

Yes, if you haven't already. The one we think there could be a problem with is UC7 pin 2 - UC9 pin 15 (Same signal line, different ICs, just to make sure the signal is present at both ends).

Disregard anything I said about UC9 pins 1 through 10, I was obviously having a bad day yesterday. As long as we have the expected signal on UC7 pin 2 / UC9 pin 15, the 74LS145 remains the prime suspect.
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Old 11th Apr 2021, 5:07 pm   #1558
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Default Re: Non-working Commodore PET 3016

Here's UC9/15 and UC7/2 compared.

Is it worth having the other UC9/UC7 pins as a comparison (ie both on the same screen)?

Colin.


Quote:
Originally Posted by SiriusHardware View Post
Yes, if you haven't already. The one we think there could be a problem with is UC7 pin 2 - UC9 pin 15 (Same signal line, different ICs, just to make sure the signal is present at both ends).

Disregard anything I said about UC9 pins 1 through 10, I was obviously having a bad day yesterday. As long as we have the expected signal on UC7 pin 2 / UC9 pin 15, the 74LS145 remains the prime suspect.
Attached Thumbnails
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Name:	UC9 pin 15 yellow UC7 pin 2 green - 20210411.jpg
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ID:	231497  
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Old 11th Apr 2021, 5:28 pm   #1559
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Default Re: Non-working Commodore PET 3016

Quote:
Originally Posted by ScottishColin View Post
Two screenshots attached.
If I'm reading it right, that pin is going cleanly low five times in a row for about 125Ás (?) each, about every 17ms; which is exactly what I would expect to see from the sequence 0000-0001-0010-0011-0100-0101-0110-0111-1000-1001 being written to pins 12-15 of UC9.

I'd expect pin 14 to stay low most of the time and periodically make two high-going pulses of 250Ás (or at any rate twice whatever the original duration was, if I misread it); pin 13 to stay low most of the time with high-going pulses of 500Ás; and pin 12 to stay high most of the time with periodic low-going pulses of 1ms. If you keep pin 15 connected at the same time as the other pin under test, it should be possible to see the relationship between the bits.

This suggests UC9 is getting the right inputs, which is a relief as it means UC7 is probably good. Probing the outputs of UC9 would need resistors adding as discussed above, but I'd happily condemn it on the evidence above alone. Still, if you are feeling sufficiently curious (or masochistic ), each of pins 1-11 (except 8) should show a single low-going pulse of 125Ás every 17ms, lined up under one of the ten steps of the pin 15 sequence, if UC9 were good.
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Old 11th Apr 2021, 5:54 pm   #1560
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Default Re: Non-working Commodore PET 3016

Attached is UC9/15 compared to 14,13 and 12 - is that what you're after?

Colin.

Quote:
Originally Posted by julie_m View Post
Quote:
Originally Posted by ScottishColin View Post
Two screenshots attached.
If I'm reading it right, that pin is going cleanly low five times in a row for about 125Ás (?) each, about every 17ms; which is exactly what I would expect to see from the sequence 0000-0001-0010-0011-0100-0101-0110-0111-1000-1001 being written to pins 12-15 of UC9.

I'd expect pin 14 to stay low most of the time and periodically make two high-going pulses of 250Ás (or at any rate twice whatever the original duration was, if I misread it); pin 13 to stay low most of the time with high-going pulses of 500Ás; and pin 12 to stay high most of the time with periodic low-going pulses of 1ms. If you keep pin 15 connected at the same time as the other pin under test, it should be possible to see the relationship between the bits.

This suggests UC9 is getting the right inputs, which is a relief as it means UC7 is probably good. Probing the outputs of UC9 would need resistors adding as discussed above, but I'd happily condemn it on the evidence above alone. Still, if you are feeling sufficiently curious (or masochistic ), each of pins 1-11 (except 8) should show a single low-going pulse of 125Ás every 17ms, lined up under one of the ten steps of the pin 15 sequence, if UC9 were good.
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Name:	UC9 pin 15 yellow pin 14 green - 20210411.jpg
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ID:	231503   Click image for larger version

Name:	UC9 pin 15 yellow pin 13 green - 20210411.jpg
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ID:	231504   Click image for larger version

Name:	UC9 pin 15 yellow pin 12 green - 20210411.jpg
Views:	16
Size:	47.8 KB
ID:	231505  
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