Commodore PET 8032 repair. ROM/RAM/IO and more faults fixed!

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Complete repair of a CBM 8032 (Universal PET) motherboard S/N: WG17291
Faults found:
- NE555 on reset circuit
- M53354 TTL decoder IC
- 2 x MOS6520 PIA
- 2 x MOS masked programmed ROMs
- HM4716AP DRAM IC
Timeline:
00:00 - Welcome
00:42 - Mechanical issues
01:16 - Voltage checks
01:43 - CPU reset missing
04:07 - Address decoder fault
09:03 - First bad ROM
10:21 - First bad MOS6520
13:15 - Second bad ROM
17:41 - It lives! (w/ a bad 6520)
20:38 - Fixing IEEE-488
22:26 - Bad RAM IC
PET RAM/ROM daughterboard:
• Commodore PET RAM/ROM ...
8-bit NOP generator introduction:
• 8 bit troubleshooting ...
Mr. Li's 6502 NOP generator socket:
www.laser.com/product_info.ph...
Re-tinning edge connectors:
• Gallag bootleg (Galag...
Re-tinning faster method:
• Atari Asteroids arcade...
Music on this video:
Guava Juice by Aaron Lieberman

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Опубликовано:

30 июл 2024

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Комментарии : 29

@marcopantanetti4053 2 года назад

Congratulations Francesco, it's always a pleasure to see you at work

@iz8dwf 2 года назад

Grazie Marco! :)

@mariusberger3297 2 года назад

this board really fought you all the way! great work with the repair as always, greetings from Germany!

@iz8dwf 2 года назад

Thanks for the comment! There's another board that was way more difficult than this one, it will be one of the next videos :)

@Shmbler 2 года назад

The first serious retro repair video this week. You saved the weekend ;-)

@iz8dwf 2 года назад

Hi! The only problem is always this: either I repair things or I edit videos :) So it takes a while to make new ones.

@milk-it 2 года назад

I wish more retro computer channels would do these videos. They're so helpful when it comes to learning how to diagnose and fix issues. Good stuff.

@Shmbler 2 года назад

@@iz8dwf They're perfectly fine now. Don't waste more time on editing. Spent it on more repairs ;-)

@Shmbler 2 года назад

There are quite some channels that do on a regular basis. But the last few weeks, it seemed to me that only Necroware and CuriousMarc did some interesting repairs, albeit not as deep as iz8dwf usually goes. Yesterdays XT board "repair" by Adrian was also very interesting.

@iz8dwf 2 года назад

full disclosure: it takes far more time to edit than to repair :) I have a few repair videos still to edit. And repair queue is still long too.

@douro20 2 года назад

Those current tracers are expensive but very handy for locating signal lines.

@iz8dwf 2 года назад

Luckily I've got mine some years ago when these tools weren't that famous and expensive :)

@deborahberi3249 2 года назад

I'm glad it was you working on this PET...what a complicated series of issues and great work as always! -Mark.

@iz8dwf 2 года назад

Hi Mark, thanks! Patience and perseverance always pay :)

@schlika 2 года назад

Super interesting, learned a lot, thanks !

@iz8dwf 2 года назад

Glad it was helpful!

@DrDavesDiversions 2 года назад

Nice job, Frank!

@iz8dwf 2 года назад

Hi! Thanks!

@RudysRetroIntel 2 года назад

Always excited to see you fantastic videos! How did you connect an external monitor? Been look for this setup for a while. Grazie!

@iz8dwf 2 года назад

Hi, thanks for the comment! That monitor is a dual sync (15KHz/20KHz) composite and TTL inputs. Since the universal PETs have similar scan frequencies (around 20 KHz) I could simply adapt the TTL signals out of the PET motherboard. It needs some TTL inverter on syncs only.

@MattKasdorf 2 года назад

Thanks! Great video. Is information on your test software and IEEE and user port hardware available?

@iz8dwf 2 года назад

Hi! The IEEE-488 program is copied from this book: www.primrosebank.net/computers/pet/documents/PET_and_the_IEEE488_Bus_text.pdf User port transfer program is cbmlink: www.zimmers.net/anonftp/pub/cbm/crossplatform/transfer/C2N232/cbmlink.html

@Mr_ToR Год назад

Hi Francesco, I have an interesting question. The schematic indicates two separate parts. 74LS74 (UB2, UB1) and 74S74 (UD2, UE4). Datasheets seem very similar except 74LS74 can work at 25MHz and 74S74 can work at 110MHz. This seems very strange. I thought the 74LS series were faster than 74S series. Can I just use 74F series instead? as in 74F74 for 74LS74 and 74S74? There is also a 74S04 which is very obsolete and hard to find. Can I use a 74F04 instead? Thanks a lot.

@iz8dwf Год назад

Hi! UD2 and UE4 are used in the clock generator circuits, they have used the faster family to introduce the least amount of delay on these signals. 74S is the first schottky TTL family, very fast and it was introduced before the 74LS one. You can use 74F parts to substitute the old 74S if you don't have the correct one. You cannot use 74F (generally speaking) parts in place of 74LS ones. The much smaller delay could in many cases give timing errors (for example violate the Thold on RAM/ROM access etc..). 74HCT family is a good substitute for 74LS parts most of the times. However, 74LS ICs are too easy to be found to bother in my opinion.

@Mr_ToR Год назад

@@iz8dwf Thank you so much 👍👍

@Mr_ToR Год назад

@@iz8dwf Dear Francesco, I hope I'm not disturbing but I found a peculiarity in my universal board. The schematic indicates that U3 is a 74LS138 but my board had originally factory installed 74S138 at U3. That's the decoder setting read/write and choosing even/odd display ram for video latch and video data buffer. Installed 74S138 is 8ns/245mW but schemaic 74LS138 is 21ns/32mW. Which do you think is the correct one? Schematic or the factory? also hotter faster or cooler slower? 🙂

@iz8dwf Год назад

@@Mr_ToR Hi, if you're sure the IC was installed by the factory (in other words, if it has not been substituted later by someone else), always the factory usually has more authority over the schematic. I think that on 80 columns PETs the extra speed might be needed, but take it just as my feeling. Short answer: always trust parts that have been installed by the factory on a working machine.