A1200 flashing/toggling green screen

[DanBy]

Hi,

I'm slowly fixing(?) a non-working A1200 motherboard. It came with all the caps removed and the previous owners assurance that "it was working before I took the caps off". Which may or may not be true. I've manage to recap it and repair some issues with broken pads. Now switching it on for the first time I get a green screen.

The green screen gives me about 2 second of bright green, then 1 second of a darker green. And it alternates this way. Does this indicate a specific error? I'm aware the brighter green is usually a memory/CIA issue. But this flashing?

Is it just quicker/easier to get a diagrom and the necessary lead?

[DanBy]

Yeah, this is a 1A board. Cursory inspection doesn't indicate any broken traces but I haven't done a close inspection nor got down to continuity checking. In the main I'd say the board looks clean and in good condition .

Possibly some cap leakage has damaged the board but there's really nothing obvious visually around any caps, though 3 pads for caps were gone/missing. Not sure what caused that, previous owner was trying to recap that board so they may have just lifted them. As per that other thread I've bridged some different caps across the relevant circuit to get round the missing pad issue. For the other surface mount caps I wouldn't say my soldering job is amazing (it's been a while) but I'm confident they are correctly in palce

[MigaTech]

Do any of the IC's get warm and have you tried pressing down on any of them? It could be dry joints around the SMT.

[DanBy]

Originally Posted by MigaTech

Do any of the IC's get warm and have you tried pressing down on any of them? It could be dry joints around the SMT.

After 10 mins of being on I would not say there is any sign of any IC being unduly hot. The CIA at U8 is perhaps a touch warmer than the one at U7 but I wouldn't describe either as hot. They aren't even noticeably warm. All four RAM chips feel like they aren't generating any heat. The two hottest ICs on the board are the CPU and Alice.

I've additionally power cycled the board holding each IC in place to see if that helped a dry joint and there's no change in behaviour.

[MigaTech]

At least you can rule this out as a possible fault. Alice and the CPU usually get warm, so that's normal.

Would you say the green is RAM and the CIA?

[DanBy]

Originally Posted by MigaTech

At least you can rule this out as a possible fault. Alice and the CPU usually get warm, so that's normal.

Would you say the green is RAM and the CIA?

It's the usual bright green associated with RAM/CIA issues.

Now that I've watched it a bit more I think the darker green is a result of some kind of power cycling it is doing.

[supaduper]

Are the Ras and Cas signals present ? Budgie generates these and you can see if they are there on TP 2(test points) bottom left on the board, Ras is no 7 from Left and Cas no 8

[DanBy]

Originally Posted by supaduper

Are the Ras and Cas signals present ? Budgie generates these and you can see if they are there on TP 2(test points) bottom left on the board, Ras is no 7 from Left and Cas no 8

Does this need an oscilloscope? I don't have one to hand but can acquire

[supaduper]

No you can use a cheap Logic Analyser if you have one as that will indicate if there is a signal

https://mega.nz/file/NlZjWTwD#ZUWDYG...KGHKpOe950F5Lg

[DanBy]

Originally Posted by supaduper

No you can use a cheap Logic Analyser if you have one as that will indicate if there is a signal

https://mega.nz/file/NlZjWTwD#ZUWDYG...KGHKpOe950F5Lg

Great, I'll just pick one up that that covers up to say 20Mhz?

[DanBy]

Originally Posted by supaduper

No you can use a cheap Logic Analyser if you have one as that will indicate if there is a signal

https://mega.nz/file/NlZjWTwD#ZUWDYG...KGHKpOe950F5Lg

ok
Now I have the probe where is a good place to connect it? I'm not seeing any obvious places to connect the 5v (or 12v) leads. Or the gnd for that matter

[supaduper]

Use the Floppy connector, it has 12v and 5v and GND on it

[DanBy]

Originally Posted by supaduper

Use the Floppy connector, it has 12v and 5v and GND on it

Oh yeah! Thanks

[DanBy]

Originally Posted by supaduper

Are the Ras and Cas signals present ? Budgie generates these and you can see if they are there on TP 2(test points) bottom left on the board, Ras is no 7 from Left and Cas no 8

Ok, finally got some time to tinker with this and both Test Point read High with the logic probe

[supaduper]

Do they Pulse like on the Video I linked too ? or just stay high ,as there there should be a PULSE signal not just a High

[giantclam]

Did C303/C304 leak? If they did I'd be checking that area...

[DanBy]

Originally Posted by supaduper

Do they Pulse like on the Video I linked too ? or just stay high ,as there there should be a PULSE signal not just a High

High only, no pulsing

[DanBy]

Originally Posted by giantclam

Did C303/C304 leak? If they did I'd be checking that area...

I don't see any leak damage around that area. I added new caps there without issue too.

[supaduper]

Originally Posted by DanBy

High only, no pulsing

well so long as you have that logic probe on the right setting normally `TTL` not CMOS then you have no cas and ras signals as you should get a pulse on the Probe.
which why you do not get a boot, so Budgie chip may be faulty

[DanBy]

Originally Posted by supaduper

well so long as you have that logic probe on the right setting normally `TTL` not CMOS then you have no cas and ras signals as you should get a pulse on the Probe.
which why you do not get a boot, so Budgie chip may be faulty

I'm confident that I have the logic probe set correctly and I definitely double checked that the amiga is TTL logic.

When I get a bit more time I'll check what signals budgie is generating