Recovered old A500

[solarmon]

But to be honest, all this tracing could be a waste if you can't get the chips confirmed to be working OK.

[stevew]

Originally Posted by solarmon

But to be honest, all this tracing could be a waste if you can't get the chips confirmed to be working OK.

I think you may be onto something here :-)

Maybe I can drive to you so we can try swapping chips over.

Also was thinking along the same lines, rather than check everything, when I turn on the Amiga with no keyboard or floppy drive attached I just get a black screen, when I plug in the keyboard I then get a green screen. You mentioned it may be a reset issue, but I'm wondering if this behaviour is related to a certain chip which may indicate that chip is faulty.

[solarmon]

Another option is to get a Diagrom. You can use that to replace the Kickstart ROM and it will load up diagnostics software:

https://www.ebay.co.uk/itm/DiagROM-V...72.m2749.l2649

[stevew]

Well do you think this is the best next course of action? if you think it will help me I'll buy one. More than happy to try chip swap as well or should I try diagrom first?

I've bought the diagrom

[stevew]

Just gave all the chips and sockets another good clean put board back into case and powered up without keyboard, green screen... oh green without keyboard this time. Oh wait, I forgot to put insulating card under motherboard, ahhhh turn off, put card under board, switched on and back to er, normal, black screen without keyboard, green with.

I'll await diagrom now..

[solarmon]

Just note that there needs to be a small mod to newer kickstart chips (including Diagrom) for rev 5 boards.

I'm just trying to determine what chips from a rev 5 board will work in a rev 6a board.

[solarmon]

Or you can get something ready made for the mod:
https://amigastore.eu/599-amiga-500-...m-adapter.html

[stevew]

Originally Posted by solarmon

Or you can get something ready made for the mod:
https://amigastore.eu/599-amiga-500-...m-adapter.html

ah yes. Thanks, maybe it would be cheaper for me to just buy some replacement chips :-)

With that in mind I've cancelled the diagrom and will have a think about what to do next as I can get a 2 or 3 working chips for the price of the diagrom + adaptor.

I think the main OCS chips will work, Paula, Gary, CIA, Denise, Agnus, as long as Denise and Agnus are not ECS versions.

[stevew]

Thanks to Solarmon for coming to help me out with my Amiga on Saturday, we managed to test my chips in his working Amiga rev6a, the only chip we struggled with was the Agnus as my 8371 produced horizontal banding (think it was a synch issue) when used in his rev 6a board and using his 8372A in my rev 5 board just produced a black screen.

[stevew]

I'm trying to fix my green screen issue and am using a logic probe on chip ram U16-U31.

On U18, U19, U22, and U25 all pins provide a signal, on the rest all but pin 2 and 14 work.

I have tested continuity to U16-31 for pin 2 and 14 and all have continuity with agnus and logic chips.

I have noticed that the pin 2 and 14 will get a brif signal when the amiga resets.

Any help much appreciated

[Vypr]

pins 2 and 14 are data in and out respectively if there's no activity on those pins it would mean that data isn't being written to or read from the chips which would result in the green screen.

[stevew]

Quick update, after knackering the U6 socket so had to replace that, I've replaced the Q711 transistor and so now the rest issue has been fixed.

I've got diagrom 1.2, it flashed full green/red screen, and with a serial connection to PC after failing every address it states "No chipram detacted"

Any help much appreciated on what to check next.

[stevew]

After some help from Chucky in deciphering the memory error I got from diagrom through the serial connection I narrowed down the issue to the top word (D8-D15), I replaced U12 and U13 but this did not solve the issue, then found the issue is with 4 of the dram chips on the board.

My next job after I receive some tested working drams is to replace the 4 faulty drams.

The game continues with this one, great learning experience though.

[stevew]

Also come to the conclusion that the floppy was moved by the repair man in 1990 as I believe the eject button for the drive was broken, he replaced it with what looks like a A2000 floppy eject button. This is shorter and so meant he mangled the case/mb etc to move the floppy drive closer towards the case side.

One of the mangled things was the floppy port lip was cut off the top case.



Repaired by carefully cutting it from a donor broken case.

[psoma]

Don’t discount the value of Diagrom. I was having green screen issues with my A600 and used Diagrom to determine the CPU was fine, but the only signal back from the RAM was 1s irrespective of what was sent to it. Turns out the RAMEN trace between Agnus and Gayle was kaput... fixed thanks to Diagrom!

[stevew]

A quick update on this, all working fine until I connected a new Amiga Kit memory expansion with Real Time Clock.

The RTC was not recognised, I tested the memory expansion in another amiga and it worked fine with RTC recognised.

I tested continuity between CNX pin 49 _CLKRD and Gary 22 - all okay, and tested continuity between CNX pin 50 _CLKWR and Gary 23 - all okay.

Set the MM to Diode test and noticed a difference between the AMIGA that recognised the RTC and the Amiga that did not.

Holding one MM probe on CNX pin 1 (VCC) and the other on CNX pin 49 (_CLKRD)
- Working RTC Amiga - MM read 0.65v
- Non working RTC Amiga - MM read OL

This lead me to look at Gary which on the non working RTC Amiga was the older Toshiba Gary, so I swapped Gary out and the problem was fixed.

I'm wondering what the Diode test showed me on the working RTC Amiga, does that show that a gate in Gary for pin 22 was connected inside Gary and the for broken gary it was stuck open, so meaning the MM showed OL?