Advice on fixing an Amiga 500+

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Steve
Posts: 274
Joined: Fri Sep 15, 2017 11:49 am

Advice on fixing an Amiga 500+

Post by Steve » Wed May 15, 2019 9:49 am

Hi guys,

Symptoms: red then green screen
Solved red screen by replacing the ROM.
New symptom: just pure green screen.

I'm new to Amigas in general and I'm trying to repair an a500+. It had a small amount of battery leakage, I removed the battery and cleaned up the board. The small gate array IC in the data path was corroded so I replaced it with a new socketed version. I checked all traces and everything was good around the leakage. All traces to Gary are good, and to the IC I replaced.

I got a spare 256k ram chip and bridged it on top of each motherboard ram chip in succession to see if one was faulty, no change still green screen every time.

I cleaned and reseated every single socketed chip.

I swapped out every custom chip from a known working a500 motherboard, but could not swap Angus as she's an incompatible model since this board is a plus variety.

I'm seeung if I can source a new Angus in the mean time.

Any other ideas?

Thx
Falcon ct60e 060 - 256mb ram - phantom bus and dsp accel // Atari TT - Thunder and Storm IDE 64mb ram - Lightning VME - USB LAN - Ati Mach64 2mb // Atari STM 4160 - 4MB ram - 16Mhz exxos 1.5 booster - Ultrasatan

Maximilian
Posts: 102
Joined: Thu Feb 28, 2019 5:02 pm

Re: Advice on fixing an Amiga 500+

Post by Maximilian » Wed May 15, 2019 8:16 pm

Well, Green is a problem with Chipram normally, how many times does the power led blink?

Did you replace the kickstart with exactly the same chip?

Personally i would check:
1. The pcb again with the help of http://www.amigapcb.org/
2. Using Diagrom
3. The Agnus socket

Piggybacking ram will only work if pins are open after a failure, and if a bit is shorted to GND or VCC it will not help.

Maximilian
Posts: 102
Joined: Thu Feb 28, 2019 5:02 pm

Re: Advice on fixing an Amiga 500+

Post by Maximilian » Wed May 15, 2019 10:22 pm

Maximilian wrote:
Wed May 15, 2019 8:16 pm
how many times does the power led blink?
Disregard that, was thinking of another machine :-)

Did you swap the Cia's?, there is a OVL line that can cause green screen problems..

Steve
Posts: 274
Joined: Fri Sep 15, 2017 11:49 am

Re: Advice on fixing an Amiga 500+

Post by Steve » Thu May 16, 2019 1:05 pm

I replaced the kick start with a 1.2 one from my spare a500. I did try swapping the Cias, no change. I'll check that website you posted.
Falcon ct60e 060 - 256mb ram - phantom bus and dsp accel // Atari TT - Thunder and Storm IDE 64mb ram - Lightning VME - USB LAN - Ati Mach64 2mb // Atari STM 4160 - 4MB ram - 16Mhz exxos 1.5 booster - Ultrasatan

Maximilian
Posts: 102
Joined: Thu Feb 28, 2019 5:02 pm

Re: Advice on fixing an Amiga 500+

Post by Maximilian » Thu May 16, 2019 4:51 pm

Ok, make sure you have 1mb of ram installed as a max as KS 1.2 does not support 2MB chip if I remember correctly.
(No mem expansion inserted)

Did you try(with the correct extractor tool) to extract the Agnus and inspect it's socket?, sometimes just taking it out and putting it back is enough.

I have a creepy feeling that there is still something wrong around the battery damage, check the previously mentioned site.

Steve
Posts: 274
Joined: Fri Sep 15, 2017 11:49 am

Re: Advice on fixing an Amiga 500+

Post by Steve » Sat Jun 01, 2019 8:31 pm

Maximilian wrote:
Thu May 16, 2019 4:51 pm
I have a creepy feeling that there is still something wrong around the battery damage, check the previously mentioned site.
Today on this lovely Saturday I decided to give it another crack. I carefully sifted through all the traces using that AMAZING website.. I can't believe how brilliant it is. The Amiga community sure gets some love... Anyway, I patched up some traces that had either been affected by the acid or had broken on the middle/inside layer. There were quite a few, the machine is not fixed yet but the symptoms have changed.

Before: Green / Red screen & flashing green led on keyboard constantly
After: Black screen, no output sync, solid green led on the keyboard.
(One time I turned it on, oddly, the disk activity orange led started flashing like it was reading, then stopped. It only did this once.)

I'll post some pics of my handy work, I'll tidy my wires up after I get it working...
IMG_20190601_200551.jpg
IMG_20190601_200551.jpg (406.42 KiB) Viewed 1181 times
IMG_20190601_175431.jpg
IMG_20190601_175431.jpg (282.59 KiB) Viewed 1181 times
IMG_20190601_175416.jpg
IMG_20190601_175416.jpg (268.93 KiB) Viewed 1181 times
Falcon ct60e 060 - 256mb ram - phantom bus and dsp accel // Atari TT - Thunder and Storm IDE 64mb ram - Lightning VME - USB LAN - Ati Mach64 2mb // Atari STM 4160 - 4MB ram - 16Mhz exxos 1.5 booster - Ultrasatan

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Daedalus
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Location: Glasgow, Scotland
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Re: Advice on fixing an Amiga 500+

Post by Daedalus » Sat Jun 01, 2019 10:20 pm

Hmmm... First thing I would suggest is getting hold of a DiagROM and null modem cable. DiagROM replaces the Kickstart chip for diagnostics, and can start with a bare minimum of hardware working. With a green screen for example, you can look at the serial output on another machine and it will show at which addresses the chip RAM test is failing. From this it's usually possible to decipher which bits are affected on the address or data bus.

Nice job with the green coating ;) I know you say you checked Gary already, but chip RAM errors and dead black screens are both symptoms I've seen of a bad Gary socket, where corrosion from a battery leak has caused the contacts to lose their springiness and tarnished their surfaces. From the photos, this seems like a mildly damaged board compared to some I've brought back, so I'm sure the fault is there somewhere. Check again that you've made all the connections you need to the correct point - it's easy to get muddled when you're flipping the board over an back, counting pins that belong to the decoupling capacitors instead of the chip or what not.

On one A500+ I fixed, there was a bad connection right at the via of one pin of buffer logic chips on the RAM bus. I couldn't see it because the pressure of touching a multimeter probe to the chip's pin was enough to close the circuit and give a positive conductivity reading, which of course stopped again once I took away the probe. Took a bit of head scratching, that one ;)

Steve
Posts: 274
Joined: Fri Sep 15, 2017 11:49 am

Re: Advice on fixing an Amiga 500+

Post by Steve » Sat Jun 01, 2019 11:57 pm

Thanks for the advice. I'll double check the gary socket and logic chips. I'll also look into a diagrom.
Falcon ct60e 060 - 256mb ram - phantom bus and dsp accel // Atari TT - Thunder and Storm IDE 64mb ram - Lightning VME - USB LAN - Ati Mach64 2mb // Atari STM 4160 - 4MB ram - 16Mhz exxos 1.5 booster - Ultrasatan

Maximilian
Posts: 102
Joined: Thu Feb 28, 2019 5:02 pm

Re: Advice on fixing an Amiga 500+

Post by Maximilian » Sun Jun 02, 2019 12:45 pm

Steve wrote:
Sat Jun 01, 2019 8:31 pm
Today on this lovely Saturday I decided to give it another crack.
The coating looks very good indeed, what did you use?

PaulJ_2.0
Posts: 143
Joined: Sat May 11, 2019 11:32 pm

Re: Advice on fixing an Amiga 500+

Post by PaulJ_2.0 » Sun Jun 02, 2019 1:11 pm

A protip for repairing traces with wire is to use enamelled wire, you can find it on old transformers and coils that almost everyone would have lying around.
Using normal wire with plastic coating isnt that great as its easy for a pin to penetrate and short, the wire is usually too bendy so hard to shape and its also harder to solder onto smaller pins and into vias.

You can buy spools of it made for the purpose of trace repair, but it literally is just transformer/coil wire, spend a little time unwinding one and reuse it.
https://www.ebay.co.uk/itm/252962939163

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