A500 black screen

[Misko78]

Got one rev6 board but when i power it up it just gives black screen.


- pulled out and reseated all chips (with proper extractors)
- Used contact cleaner on sockets

Screen is still black. But the TV recognizes the signal is RGB and gives info on screen.

CPU, Denise and memory are cold
Agnus, Paula and Gary are warm
Odd CIA is buring hot after couple of seconds
Even CIA is hot but i can hold a finger on it
When i swap them, then the even CIA is burning hot and odd CIA is hot but not that much.

Should i try known good CIAs in this board or not? Or maybe try out CIAs in known working board?

[jurassicman]

Have you tried the composite output? Does the Floppy Disk Drive tick?

[Misko78]

Composite not working, haven't tried the floppy because i can't find floppy power cable anywhere. I'll make one tomorrow.

[Misko78]

Well, tested the chips in working board:

CPU - OK
Denise - BAD (grays are purple)
Paula - OK
ROM - OK
CIA #1 - BAD (gets hot and floppy not working)
CIA #2 - BAD (gets hot and floppy not working)
Gary - BAD (no boot at all)
Agnus - BAD (green broken wavy screen)

[admiral]

Originally Posted by Misko78

Well, tested the chips in working board:

CPU - OK
Denise - BAD (grays are purple)
Paula - OK
ROM - OK
CIA #1 - BAD (gets hot and floppy not working)
CIA #2 - BAD (gets hot and floppy not working)
Gary - BAD (no boot at all)
Agnus - BAD (green broken wavy screen)

Christ. That's terrible.

The question is... what destroyed all these chips?

[Jope]

Could have been a power supply over voltage.

[Misko78]

Who knows, i bought this junker for 10€, board look very good. At least now i have CPU, Paula and ROM spares.

[admiral]

Originally Posted by Jope

Could have been a power supply over voltage.

If it was a C64 supply. But Amiga supplies don't have that failure mode, that I am aware of.

[Misko78]

OK, i got another "untested" board, also 6a.

This one starts but it takes a long time ~2minutes of black screen thank two gray screens, white one, and in the end KS 1.3 screen.

Board had corrosion on memory expansion connector, some gunk around reset section of the board. Someone cut the pins of SN74LS157N piggybacked another SN74LS157N on top of the pins. I've cleaned up everything (gunk, corrosion...), took the chips out, cleaned the legs and it started with 2min delay.

Any ideas what to check? Capacitors maybe?

[admiral]

Originally Posted by Misko78

OK, i got another "untested" board, also 6a.

This one starts but it takes a long time ~2minutes of black screen thank two gray screens, white one, and in the end KS 1.3 screen.

Board had corrosion on memory expansion connector, some gunk around reset section of the board. Someone cut the pins of SN74LS157N piggybacked another SN74LS157N on top of the pins. I've cleaned up everything (gunk, corrosion...), took the chips out, cleaned the legs and it started with 2min delay.

Any ideas what to check? Capacitors maybe?

It starts meaning you can run software on it? Run keirf's amiga testkit as a start.

[Misko78]

unfortunately i don't have amigatest kit on disk, only as an image for gotek. And i can't disassemble my working amiga for now.
Tried WB and it works, tried couple of games and games work.

[admiral]

Originally Posted by Misko78

unfortunately i don't have amigatest kit on disk, only as an image for gotek. And i can't disassemble my working amiga for now.
Tried WB and it works, tried couple of games and games work.

If you have a null-modem serial cable, amigaXfer will easily and very quickly write these disks for you.

You only need the three wires (TX<>RX and GND-GND). The rest will not be used even if present.

[Misko78]

I managed to fix it. R712 was 50MOhm so it was dead, replaced it with proper 47KOhm and it booted up immediately.

[admiral]

Originally Posted by Misko78

I managed to fix it. R712 was 50MOhm so it was dead, replaced it with proper 47KOhm and it booted up immediately.

Thanks for the report. Might help somebody in the future. That's one more possible failure to look out for; I hadn't heard about resistors failing.

[Misko78]

the board from the first post is up and running again.

I managed to buy complete Amiga 500 chipset cheap and decided to try out my luck, also the PLCC socket was cracked.
All of the voltages were ok, and chips survived power on, but screen was green this time. Using piggyback method i found out that the culprit was one ram chip, as i had one old Cirrus Logic VGA card with 8 compatible dram ICs i decided to take out old dram and install sockets and plug in chips form VGA. The PLCC socket was cracked and i replaced it, to be safe in the future.This scrap board is fully operational now with 1MB of chip ram.

[jurassicman]

Great job!

[stevsurv]

Awesome! Another dead Amiga given the "breath of life". A plus!

[Misko78]

Thank you fellows!!

[Lord Aga]

Wow, an awesome journey to bring back one unfortunate Amiga back to life