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Amiga Hardware Issues and discussion / Re: Severe Graphics Issues - A500 Rev6A, DiagROM 1.2.1
« Last post by poroxius on February 01, 2026, 11:55:11 AM »Hi!
A couple of months passed since I last wrote under this post.
In the last reply, I said that I was going to check the DiagROM output with a new Paula. I connected the null modem cable to my A500's serial port and opened PuTTY. I got the DiagROM booting text and could easily use the menu.
This is what DiagROM gave me in System Info:
Information of this machine:
Dump of all readable Custom Chipset HW Registers:
BLTDDAT ($dff000): $8098 DMACONR ($dff002): $6380 VPOSR ($dff004): $A000
VHPOSR ($dff006): $9A61 DSKDATR ($dff008): $FFFF JOY0DAT ($dff00a): $0000
POT0DAT ($dff012): $0505 POT1DAT ($dff014): $0000 POTINP ($dff016): $0606
SERDATR ($dff018): $4B2D DSKBYTR ($dff01a): $9000 INTENAR ($dff01c): $4B2D
INTREQR ($dff01e): $1000 DENISEID ($dff07c): $0000 HHPOSR ($dff1dc): $0090
Workmem: $0006C478 - $0007FFFD Size: 78kB ROM size: 156kB Order: End
Chipmem workarea: $00000400 - $0007FFFF Fastmem workarea: $00000000 - $00000000
Doing ROM Checksumtest: (64K blocks, Green OK, Red Failed)
$CED3BA58 $98C6080B $3980DA0F $003EC000 $003F0000 $003F4000 $003F8000 $00DFBCEA
CPU: 68000 FPU: NONE MMU: NOT CHECKED
Is $1114 readable at addr $0 (ROM still at $0): NO
Is $1114 readable at addr $f80000 (Real ROM addr): YES
Is $1111 readable at addr $f00000 (expansion ROM addr): NO
Stuck buttons & keys etc at boot: BADPAULA
Serial: 9600 BPS - CPU: 68000 - Chip: 512kB - kBFast: 0 Base: $0006C47A
I'm still getting the P1RMB/LMB stuck at boot during the DiagROM's booting process. Everything else seems to be normal as DiagROM's menu functions normally on the serial output.
However, when I try to connect my A500 to my 1084S-P1 or SCART TV, I'm not getting any video output.
Maybe the contacts on the A500's video connector should be cleaned as I didn't do it for a couple of months now, but it's really weird as I'm not getting anything on both the 1084S and SCART output of my Sony TV.
Upon researching, black screen with DiagROM inserted suggests a faulty CPU, but as I'm getting normal and healthy serial output and strong 10 short + 1 long flash from my keyboard, I think that something might be wrong with my A500's video connector, which I will firstly check.
After I read some of my older posts on r/amiga about this issue, I remembered that I used to fix this yellow screen and boot normally by pulling out Fat Agnus with a PLCC extractor, cleaning her with IPA and reinserting her into her socket. When I reinserted her, along with pressing on other ICs, the Amiga would start working again. But, after a leg broke on that original Agnus, I replaced her with a new one, tried the same trick again, but this time it didn't work. I forgot to mention this to you in earlier replies as I totally forgot about that.
Q: Maybe it's the faulty Agnus socket that's causing this yellow screen? The pins on the socket look ok, but maybe because one of the legs broke off of Agnus, I should replace the original socket with a new one as it may also got damaged when I was pulling Agnus out?
Also, I think that it's the right time to get an oscilloscope involved and look into the data/address busses.
I did some research about what kind of an oscilloscope I should buy, but I just got confused really quickly as I never used an oscilloscope before or did any research about it, so all of the specifications were kind of advanced for me.
As the 68000 operates on 7.09MHz (for my PAL A500), I found out that I should minimally use 20MHz, but ideally should go for >50MHz just to be safe.
I also found out that I should look for an oscilloscope that has a sampling rate of >200MSa/s, DC coupling, 1MΩ input impedance, X10 + short ground probe etc.
I was thinking about that maybe I should go for an oscilloscope that YouTubers like Adrian's Digital Basement use, but they cost a lot.
Q: If you maybe know, what are the important specs I should look into when buying an oscilloscope that I will use for my A500's diagnosing? Are there any minimal values of the specs I should look out for? Would you recommend a specific oscilloscope that maybe you are using?
The oscilloscope is pretty new to me, as I have never used it before, so I'm not sure if I'm doing my research right. I wouldn't like to spend a large amount of money on a oscilloscope that would be overkill and maybe could be replaced by a cheaper one that would work the same. Or maybe I shouldn't cheap out on this.
-poroxius, February 1, 2026
A couple of months passed since I last wrote under this post.
In the last reply, I said that I was going to check the DiagROM output with a new Paula. I connected the null modem cable to my A500's serial port and opened PuTTY. I got the DiagROM booting text and could easily use the menu.
This is what DiagROM gave me in System Info:
Information of this machine:
Dump of all readable Custom Chipset HW Registers:
BLTDDAT ($dff000): $8098 DMACONR ($dff002): $6380 VPOSR ($dff004): $A000
VHPOSR ($dff006): $9A61 DSKDATR ($dff008): $FFFF JOY0DAT ($dff00a): $0000
POT0DAT ($dff012): $0505 POT1DAT ($dff014): $0000 POTINP ($dff016): $0606
SERDATR ($dff018): $4B2D DSKBYTR ($dff01a): $9000 INTENAR ($dff01c): $4B2D
INTREQR ($dff01e): $1000 DENISEID ($dff07c): $0000 HHPOSR ($dff1dc): $0090
Workmem: $0006C478 - $0007FFFD Size: 78kB ROM size: 156kB Order: End
Chipmem workarea: $00000400 - $0007FFFF Fastmem workarea: $00000000 - $00000000
Doing ROM Checksumtest: (64K blocks, Green OK, Red Failed)
$CED3BA58 $98C6080B $3980DA0F $003EC000 $003F0000 $003F4000 $003F8000 $00DFBCEA
CPU: 68000 FPU: NONE MMU: NOT CHECKED
Is $1114 readable at addr $0 (ROM still at $0): NO
Is $1114 readable at addr $f80000 (Real ROM addr): YES
Is $1111 readable at addr $f00000 (expansion ROM addr): NO
Stuck buttons & keys etc at boot: BADPAULA
Serial: 9600 BPS - CPU: 68000 - Chip: 512kB - kBFast: 0 Base: $0006C47A
I'm still getting the P1RMB/LMB stuck at boot during the DiagROM's booting process. Everything else seems to be normal as DiagROM's menu functions normally on the serial output.
However, when I try to connect my A500 to my 1084S-P1 or SCART TV, I'm not getting any video output.
Maybe the contacts on the A500's video connector should be cleaned as I didn't do it for a couple of months now, but it's really weird as I'm not getting anything on both the 1084S and SCART output of my Sony TV.
Upon researching, black screen with DiagROM inserted suggests a faulty CPU, but as I'm getting normal and healthy serial output and strong 10 short + 1 long flash from my keyboard, I think that something might be wrong with my A500's video connector, which I will firstly check.
After I read some of my older posts on r/amiga about this issue, I remembered that I used to fix this yellow screen and boot normally by pulling out Fat Agnus with a PLCC extractor, cleaning her with IPA and reinserting her into her socket. When I reinserted her, along with pressing on other ICs, the Amiga would start working again. But, after a leg broke on that original Agnus, I replaced her with a new one, tried the same trick again, but this time it didn't work. I forgot to mention this to you in earlier replies as I totally forgot about that.
Q: Maybe it's the faulty Agnus socket that's causing this yellow screen? The pins on the socket look ok, but maybe because one of the legs broke off of Agnus, I should replace the original socket with a new one as it may also got damaged when I was pulling Agnus out?
Also, I think that it's the right time to get an oscilloscope involved and look into the data/address busses.
I did some research about what kind of an oscilloscope I should buy, but I just got confused really quickly as I never used an oscilloscope before or did any research about it, so all of the specifications were kind of advanced for me.
As the 68000 operates on 7.09MHz (for my PAL A500), I found out that I should minimally use 20MHz, but ideally should go for >50MHz just to be safe.
I also found out that I should look for an oscilloscope that has a sampling rate of >200MSa/s, DC coupling, 1MΩ input impedance, X10 + short ground probe etc.
I was thinking about that maybe I should go for an oscilloscope that YouTubers like Adrian's Digital Basement use, but they cost a lot.
Q: If you maybe know, what are the important specs I should look into when buying an oscilloscope that I will use for my A500's diagnosing? Are there any minimal values of the specs I should look out for? Would you recommend a specific oscilloscope that maybe you are using?
The oscilloscope is pretty new to me, as I have never used it before, so I'm not sure if I'm doing my research right. I wouldn't like to spend a large amount of money on a oscilloscope that would be overkill and maybe could be replaced by a cheaper one that would work the same. Or maybe I shouldn't cheap out on this.
-poroxius, February 1, 2026
