19th Feb 2021, 5:37 pm | #161 |
Nonode
Join Date: May 2004
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Re: Commodore PET 2001
Sharp craft knife and fine grades of carbide paper. I've lost some of the surface texture and I didn't do too much with the smaller marks for fear of grazing the silver finish to the legend strip. All looks quite acceptable at normal viewing distances.
Alan |
21st Feb 2021, 3:29 pm | #162 |
Dekatron
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
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Re: Commodore PET 2001
It's now clear what it is that you've been doing for all the years you weren't previously playing with micros.
On the basis of that result, you can now expect all my cosmetically imperfect items... I have a few... to turn up on your doorstep some time soon. Seriously, good job, I have no idea how you did that. |
21st Feb 2021, 8:30 pm | #163 | |
Dekatron
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Re: Commodore PET 2001
Quote:
Of course, it risks tying you to one manufacturer; but that's less of an issue when that manufacturer is also you. (It's interesting to compare this idea of distributing the glue logic around the peripheral devices with the approach taken in the UK; which was to concentrate all the glue logic into a single device which could be placed close to the microprocessor and its bus signals .....)
__________________
If I have seen further than others, it is because I was standing on a pile of failed experiments. |
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21st Feb 2021, 9:21 pm | #164 |
Octode
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Re: Commodore PET 2001
I've sent off my 6540 adapter pcb to JLCPCB since they offered me a cheap deal and I will almost certainly want one or 2 for my PET when the time comes. If AJ wants to try one when they arrive I might be able to post a PCB, Although by then he will probably have his ROMulator.
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22nd Feb 2021, 7:13 pm | #165 |
Nonode
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Re: Commodore PET 2001
Just a couple more before and after datasette shots and then I promise I'll get back to trying to fix the PET itself.
Alan |
22nd Feb 2021, 11:29 pm | #166 |
Octode
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Re: Commodore PET 2001
You seem to be restoring the texture nicely!
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23rd Feb 2021, 12:36 am | #167 |
Nonode
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Re: Commodore PET 2001
Very much 'faux' texture. Since the moulding material (epoxy) inevitably has a smooth finish the first step is to rub down the original texture to a similarly smooth surface. The area is then acrylic sprayed with the final coat being applied at a distance to obtain a slightly rough surface. This would normally be undesirable but in this instance it's a useful way to trick the eye (or camera lens).
By the way, thank you for the offer of a PCB to make a ROM adapter. I'll see how it goes with the emulator and take it from there. Alan |
23rd Feb 2021, 1:53 pm | #168 |
Nonode
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Re: Commodore PET 2001
I hope the attached photo illustrates more clearly what I mean about paint spraying. It's only the raised area of the case moulding around where the keys would be that has been sprayed and therefore includes the scar repairs as well as the corner reconstruction. The second shot shows an internal view of the corner repair.
Alan PS Emulator report to follow. |
23rd Feb 2021, 5:45 pm | #169 |
Nonode
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Re: Commodore PET 2001
Duly installed the emulator and to begin with didn't have much luck but it did help to point me in the direction of one of the faulty components. I'll provide more detail when I figure out exactly what was going on. For now the PET is up and running again using the emulator's 32k of RAM and one of its ROM images (see photo).
Alan |
23rd Feb 2021, 7:25 pm | #170 |
Octode
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Re: Commodore PET 2001
That is good news that it is running again.
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23rd Feb 2021, 7:25 pm | #171 |
Octode
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Re: Commodore PET 2001
Excellent!
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23rd Feb 2021, 10:38 pm | #172 | |
Nonode
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Re: Commodore PET 2001
A few words of explanation. After installation of the emulator and with it set to use the on board RAM/ROM the PET displayed absolutely nothing. After some experimentation with jumper settings I managed to get a partially corrupted VOSSI diagnostic screen which stated that the IEEE test had failed. This pointed towards a problem with PIA2 which I then removed. Now I got a decidedly non-random character screen. A fair bit of messing around ensued and I eventually removed the four good (supposedly) 6550 system RAM chips from the main board and all was well in the world. It would seem that PIA2 and a RAM chip had failed.
Avid readers may recall that in a previous fault analysis (post #126) I stated that: Quote:
So far I'm very happy with the emulator but will report fully when I've had more of a chance to play with it. In the meantime I need to source a replacement 6520 PIA. Does anyone know if the Rockwell R6520 or the Synertec SY6520 would work in the PET 2001-8? Alan |
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24th Feb 2021, 10:35 am | #173 |
Octode
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Re: Commodore PET 2001
Its also noteworthy that the 6521 is an equivalent to the 6520, the 6821/6521 was introduced to correct a rare 'bug' in the design. The Western Digital WDC W65C21S claims to be a "High speed/Low power replacement for Motorola / Rockwell / AMI / *MOS Technology / MOSTEK / HITACHI / ST Microelectronics / GTE / CMD 6520, 6521, 6820, 6821 PIA’s" and is in current production.
I can't imagine a Rockwell of Synertec 6520 wouldn't work as the PET doesn't exactly highly stress the PIAs. |
24th Feb 2021, 10:47 am | #174 | |
Octode
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Re: Commodore PET 2001
Quote:
And it's also possible that a 6522 VIA may also work, if these are pin-compatible (will need to check), as the 6522 is really an enhanced 6520 with extra registers / timers etc. - With the 6520 falling out of use and the 6522 much more widely used (even if the extra timers etc. in it were not actually required) It seems the PET was the main user of the 6520, with commodore moving onto the 6522 in the VIC-20, before using their own 'custom' 6526 CIA for the C64 as they were rather-keen in keeping the MOS fab busy. |
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24th Feb 2021, 10:55 am | #175 |
Nonode
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Re: Commodore PET 2001
Thanks for that Slothie and Ortek. It looks like there might a few possibilities. I'll investigate further.
Alan |
24th Feb 2021, 11:47 am | #176 |
Nonode
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Re: Commodore PET 2001
It looks like the 6522 VIA isn't pin compatible and wouldn't be a drop in replacement. The WDC W65C21N PIA looks as if it might be a good bet and is available here at a reasonable price:
https://www.ebay.co.uk/itm/Western-D...wAAOSwjVhf19ZU I'm tempted to go for it. Alan |
24th Feb 2021, 1:29 pm | #177 | |
Octode
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Re: Commodore PET 2001
Quote:
The PET has 6520's and a 6522 for the user port. |
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24th Feb 2021, 2:51 pm | #178 | |
Octode
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Re: Commodore PET 2001
Quote:
Yes, I did say the 6522 was a kind of 'enhanced' 6520 - and do recall the 16 registers from my Beeb-Programming days. But I wondered if 4 of these were the same as those on the 6520 (being as it seems the INS8154 PIA can be replaced with 6522, as share they same registers, even if H/W needs changing) Just looking at the pinouts for the 6520 & 6522, it seems most pins are the same, but 6pins have changed function. With A0-A1 (for 4 registers) becoming RS0-RS3 (for 16 registers) - but on different pin-positions, although could be re-mapped. However, main issue might be CS0 (if used) is no longer on 6522 and there's only one nIRQ rather than 6520's nIRQA & nIRQB. 6521's don't seem to be that common, but 6821's should be (I'm sure I've got some, and believe I used one on a project at Uni back in the 90's) |
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24th Feb 2021, 3:26 pm | #179 |
Nonode
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Re: Commodore PET 2001
I've ordered the WDC W65C21N PIA mentioned above. Fingers crossed.
Alan |
24th Feb 2021, 4:07 pm | #180 |
Octode
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Re: Commodore PET 2001
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