10th Apr 2021, 10:23 pm | #1541 | ||
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Re: Non-working Commodore PET 3016
Quote:
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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10th Apr 2021, 11:41 pm | #1542 |
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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. |
10th Apr 2021, 11:50 pm | #1543 | |
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Re: Non-working Commodore PET 3016
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10th Apr 2021, 11:51 pm | #1544 |
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Re: Non-working Commodore PET 3016
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10th Apr 2021, 11:56 pm | #1545 | |
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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:
Quote:
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11th Apr 2021, 12:00 am | #1546 | |
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Re: Non-working Commodore PET 3016
Quote:
Would be a shame to wait until Tuesday to find it was the lack of input that caused the problem. |
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11th Apr 2021, 12:22 am | #1547 | |
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Re: Non-working Commodore PET 3016
Does there need to be keyboard activity during these tests?
Colin. Quote:
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11th Apr 2021, 1:37 am | #1548 |
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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) |
11th Apr 2021, 8:51 am | #1549 |
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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 |
11th Apr 2021, 9:11 am | #1550 |
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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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11th Apr 2021, 1:06 pm | #1551 | |
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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:
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11th Apr 2021, 5:23 pm | #1552 |
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Re: Non-working Commodore PET 3016
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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11th Apr 2021, 5:34 pm | #1553 | |
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Re: Non-working Commodore PET 3016
Two screenshots attached.
Colin. Quote:
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11th Apr 2021, 5:35 pm | #1554 | |
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Re: Non-working Commodore PET 3016
I managed to borrow some from my better half ta. Tip noted though.
Colin. Quote:
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11th Apr 2021, 5:37 pm | #1555 |
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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. |
11th Apr 2021, 5:38 pm | #1556 | |
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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:
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11th Apr 2021, 5:52 pm | #1557 |
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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. |
11th Apr 2021, 6:07 pm | #1558 | |
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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:
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11th Apr 2021, 6:28 pm | #1559 |
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Re: Non-working Commodore PET 3016
If I'm reading it right, that pin is going cleanly low five times in a row for about 125µs (?) 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 250µs (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 500µs; 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 125µs every 17ms, lined up under one of the ten steps of the pin 15 sequence, if UC9 were good.
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11th Apr 2021, 6:54 pm | #1560 | |
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Re: Non-working Commodore PET 3016
Attached is UC9/15 compared to 14,13 and 12 - is that what you're after?
Colin. Quote:
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