Resurrecting a 500

[spacey]

I'm looking to try to get my old 500 up and running again. When I first tried it recently, the power light just blinked on and off repeatedly and nothing else happened. I opened it up and pressed the chips in in case they had come loose over the years. I also removed the 512K fast ram expansion in case that was causing problems. Now the power light is solid, I get a blank white screen and the floppy drive clicks once and that's it.

I have a feeling it had developed a fault many years ago even before being shoved in the attic when I moved on to my (still working) 1200.

Is there anything obvious I should try? Anything I can do to narrow down what's wrong?

[Codetsu]

white is CPU failure error
remove it and check contacts
and then put it back usual that fix it

if CPU is broken new one cost 1-8€

[plasmab]

Personally I use DiagROM to figure out whats up. Its a ROM replacement that spits error codes out of everything thats working.

www.diagrom.com

Chucky will burn you a rom for a small fee and send it to you if you contact him.

[Toni Wilen]

Do you mean white screen immediately after powerup or does it cycle usual colors (black, dark grey, white) and then it hangs?

[spacey]

thanks guys! will have a go at removing & re-inserting the CPU.

toni: ahh it goes dark grey, white, grey, light grey then white.. so seems like a pretty standard startup other than finishing on a white screen and nothing else?

[spacey]

this is probably a dumb question, but if it is a faulty CPU and that's the only issue, could i use a, say, ACA500plus without replacing the CPU? or do accelerators like that require a functioning CPU on the main board?

[nobody]

I would look the PSU first. Take it to some electronics guy to check if it's ok. Too old, maybe some capacitor is failing there.

[dalek]

if you get to white screen your floppy drive might be broken. Try unplugging your floppy drive, turn on the machine and wait a few minutes and see if get a insert disk screen.

[Toni Wilen]

Initial instant white does not mean CPU fault, it can only mean "something is wrong"

Colors are set by the CPU so if CPU does not work, initial power up color stays visible (which can be white or black or something else, depends on Denise revision etc..)

Try swapping CIA chips next. (Put CIA-A in place of CIA-B and vice versa, both CIA chips are identical).

Did you wait long enough? There is very long delay (30s+) if DF0: does not respond before insert WB screen appears.

[plasmab]

Strongly recommend DiagROM and a serial cable. Will save you a lot of anecdotal diagnoses


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[spacey]

what the.. how did 4 months pass since i was last able to look into this.. this year is going too fast.

so i finally got a chance to try out disconnecting the floppy and swapping the CIAs. before i did anything i powered it on to check the symptoms were the same and... they weren't. this time it was going straight to a green screen, with the power light flashing 10 short, 1 long.

i'm guessing that's worse than how it was.

after googling, it seems that the solid green screen indicated something with agnus?

i tried disconnecting the floppy and swapping the CIAs which didn't change things.. i had another go at pressing the various chips incl agnus in in case they had come loose.. but when i put all back together and powered it on once more, i got a flashing screen which eventually settled on solid red. same pattern of the blinking power light tho.

anyone see this kind of thing before?

i was pretty careful when going about this, incl against static.. but i may have just made things worse.

[spacey]

huh.. ok.. so i figured i'd try powering it on one last time and this time it went to the kickstart 1.2 screen, floppy drive doing the normal clicking, but the screen colours were messed up (light purple mainly).. then after about 20 secs the screen went blank and the drive stopped clicking.. i power cycled it and it's back to 10 short 1 long power light flashes.. that seems to be the only consistent(ish) thing.

[fordav1]

since it worked for a while and you just swapped the CIAs, it can mean one of your CIAs is bad or a bad connection on sockets and chips and removing and replacing the CIAs temporarily fixed it. That is always temporary. Pull all of the chips that are in sockets one by one, clean the legs with some very fine sandpaper (or something similar) then put the chips back in and maybe your problem will be solved.
A purple screen means green is missing. Re-seat your cable that goes to the computer and monitor. If you have a 1084S-P1 it's more than likely that the DB9 connector on the circuit board inside the monitor has cracked joints. This monitor is known to have cracked joints because the connector has no solid support fixings to the case, it is just sitting there on the circuit board soldered in. After a few years of tugging on the cable the solder joints crack and you get missing colors. Re-solder all the connections on the DB9 inside the monitor and that may fix the issue.
The same issue can also happen on older 1081/1084 monitors that have a SCART connector and jiggling or re-seating the SCART end can fix it. The fact that you saw white (white = red+green+blue) means the color issue is a bad connection on the video connectors on Amiga or monitor or cable.

[spacey]

brilliant, thank you! i'll give those things a shot.

and yeah, i was indeed using a 1084S... and i have been getting colour weirdness on it when i've had it connected to my fully functioning 1200 and 2000.. i assumed it was the cable i was using - i ordered a new one recently, but haven't received it yet.. but the issue you described makes a lot more sense!

[fordav1]

Look on the back of the monitor. If you see "1084S-P1" then it's not the cable it's the DB9 connector that has come loose. the DB9 can be re-soldered without having to disassemble the monitor. You can get access to the solder points on the back of the circuit board by just removing the back of the case and re-solder them. Before you do that, push the connector down against the board then re-solder it while holding it there and also re-solder the big outer lugs that hold the connector to the circuit board. be careful that you do not touch the circuit board *anywhere* with your hand otherwise you can get a shock from capacitors that hold their charge. this is specific to the 1084S-P1 because the power supply is part of the monitor circuit board, whereas on other models of Commodore monitors the power supply is separate and poses less of a risk (obviously providing you don't touch the power supply board ;-)
Just don't touch the board with your hand and you'll be ok.
If it has a SCART connector then it is usually the SCART end of the cable that is dodgy.

[spacey]

ok.. i bought a PLCC extractor to in order to get at agnus.. i figured i was in for a long session of taking the chips out, giving their pins a clean, replacing the kickstart with a 3.1 i bought.. i had a spare couple of minutes just now so i thought i'd try removing agnus in case there were any difficulties which i could then go away and research...

anyway, after removing & refitting agnus i powered on the machine just to see and... it works! kickstart screen came up, disk drive clicking away.. well, i get the screen flashing purple etc like before, but haven't had a chance to look at the monitor. the drive itself seems unable to read disks, but i swapped it out for a gotek and that all works great.

next steps are to replace the kickstart.. probably should open up the 1mb ram expansion and check the clock battery.

at any rate, this has really made my day. so great to see the old girl running again. thanks for all the help!