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Amiga Hardware Issues and discussion / Re: Severe Graphics Issues - A500 Rev6A, DiagROM 1.2.1
« Last post by Castellen on February 01, 2026, 07:46:37 PM »From a quick re-read of the last few posts, the key point summary is:
- The system is fundamentally alive as there was/is good serial data out with DiagROM
- DiagROM highlighted a problem with the four analogue to digital inputs at Paula/8364
- You confirmed that the four analogue inputs indeed showed around 0V instead of the expected ~5V
- This suggested a problem with Paula/8364
- You bought a (used or unknown condition??) 8364 but had no serial output with that replacement part
- The supply voltage at the replacement 8364 was measured to be ~3.6V, significantly lower than expected
- There's also some kind of uncertainty around the IC sockets, with possible contamination??
This would suggest:
1. The original 8364 is still defective, sounds as though that part is still fitted?
2. The replacement 8364 is also defective, as ~3.6V measured at the supply pin suggests it's drawing excessive current, and there's no serial data output
3. The CPU, ROM, most of the data/address bus, etc, is likely OK as the serial data out looks sane
Buying an oscilloscope at this point is not likely to help, especially as you're not well experienced with using one, and I don't have the time or patience to run a 'my first oscilloscope' training course via countless posts on a public forum. You absolutely need to know what you're looking for, in addition to knowing how to drive the instrument.
From the thread title, there was also some kind of graphics corruption thing happening. I didn't read back far enough to recall what was going on, but it's possible there's a second problem in addition to the suspected issues with the original 8364.
The simplest way forward with diagnosing this would be get access to a working A500 or A2000 that you can test the suspect 8364 in (both the original and the replacement), and if it's confirmed they're defective, then put the working 8364 from the A500/A2000 into your A500, then see if the DiagROM output looks normal. If it does, see if you can boot Workbench, etc. Or see if there are further problems.
Another option is to send the A500 main board for repair. I can do this, though freight to NZ has become more expensive. There are some Amiga retailers in Europe who advertise repairs which may be a lower cost option.
- The system is fundamentally alive as there was/is good serial data out with DiagROM
- DiagROM highlighted a problem with the four analogue to digital inputs at Paula/8364
- You confirmed that the four analogue inputs indeed showed around 0V instead of the expected ~5V
- This suggested a problem with Paula/8364
- You bought a (used or unknown condition??) 8364 but had no serial output with that replacement part
- The supply voltage at the replacement 8364 was measured to be ~3.6V, significantly lower than expected
- There's also some kind of uncertainty around the IC sockets, with possible contamination??
This would suggest:
1. The original 8364 is still defective, sounds as though that part is still fitted?
2. The replacement 8364 is also defective, as ~3.6V measured at the supply pin suggests it's drawing excessive current, and there's no serial data output
3. The CPU, ROM, most of the data/address bus, etc, is likely OK as the serial data out looks sane
Buying an oscilloscope at this point is not likely to help, especially as you're not well experienced with using one, and I don't have the time or patience to run a 'my first oscilloscope' training course via countless posts on a public forum. You absolutely need to know what you're looking for, in addition to knowing how to drive the instrument.
From the thread title, there was also some kind of graphics corruption thing happening. I didn't read back far enough to recall what was going on, but it's possible there's a second problem in addition to the suspected issues with the original 8364.
The simplest way forward with diagnosing this would be get access to a working A500 or A2000 that you can test the suspect 8364 in (both the original and the replacement), and if it's confirmed they're defective, then put the working 8364 from the A500/A2000 into your A500, then see if the DiagROM output looks normal. If it does, see if you can boot Workbench, etc. Or see if there are further problems.
Another option is to send the A500 main board for repair. I can do this, though freight to NZ has become more expensive. There are some Amiga retailers in Europe who advertise repairs which may be a lower cost option.
