Pleas help ..... a very poorly A500

[woodycool]

Hi guys,

I've just had one of those mornings where nothing works at all!

I fired on my A500 and was greeted with this:


(click for larger image)

Tried 2.04, 2.05 and 3.1 ROMs - get the above picture.
Also tried a 1.2 and a 1.3 ROM - both produced a plain white screen.

Putting a floppy in the drive and it boots but the output from the machine is a complete mess.

The machine is an A500 rev 6 (iirc) - the same board as used in an A500 Plus but with only 512KB, also, the machine is ECS.

I've completely removed and reseated all the socketed chips.

I've tried three different PSUs (a customer PC converted thing, a 'light weight' A500 and a 'heavy' A500) .... all reveal the same problem

If I have my A570 (CD-ROM drive for A500) attached, I just get a black screen when that's powered on.

Any help appreciated please! Is it likely to be fixable or should I just find another A500 motherboard?

Thanks
woody.cool

 

[quarkx]

Just off the top of my head, I would say check the Denise. Its a video problem, so swap it out, or if you have an Indi, slap that on and check.
If you swap and nothing changes, carefully go through the Mobo on a physical visual inspection, caps or a broken trace somewhere.
Thats where I would start. anyway.

 

[Exilent]

Could be the Denise, which handles the video output.

 

[woodycool]

Damn, I don't have a spare Denise chip Well, don't think so anyway.
Will the Denise chip from an A1500 do?

Initial visual inspection looks fine - no signs of bulging caps and no sign of any damage (or broken tracks)

 

[quarkx]

Damn, I don't have a spare Denise chip Well, don't think so anyway.
Will the Denise chip from an A1500 do?

Initial visual inspection looks fine - no signs of bulging caps and no sign of any damage (or broken tracks)

should be ok as long they are both the same revision. I am just guessing here. According to the BBoAH, there is no difference between the A2000 and the A500 Denise

 

[woodycool]

Swapped the Denise chip with the one in my A1500 - still got the same issue, so not the Denise chip
Any more ideas please?

 

[quarkx]

Hopefully you have done this, so I am not stating the obvious, but have you checked the cable connections both at the Amiga and on the back of the monitor with the unit on, to see if output changes.
I know, I am just going over the simplest/obvious first.

 

[woodycool]

Yes, yes I have.
Also, said cable and same display are fine on my A600, A1200 and A1500.

 

[quarkx]

I would next try CPU swap, this way we are eliminating one by one the possibilities
We know its not cables/ power supply or Denies. We can not see any burnt, scotched traces or bad caps, so next we eliminate the CPU and custom chips that we can swap.

 

[SpeedGeek]

Did you try disconnecting the A570? If you have a trap door memory expansion remove that also. The next thing to look for is some bad chip ram but I would try to re-seat Fat Agnus first and then see if any of the RAM chips run hotter than the others.

 

[Zetr0]

@SpeedGeek

I was just about to mention CHIP RAM as well!

@woody

If you need a Denise hit me up in PM and I will send you a spare.

 

[woodycool]

@SpeedGeek

I was just about to mention CHIP RAM as well!

@woody

If you need a Denise hit me up in PM and I will send you a spare.

I've found the problem.

I swapped all custom chips with my A1500, with the exception of one, the Angus chip.
My A1500 was without Angus chip, as the Megi-Chip that was in it got broke when I was carelessly installing something in the A1500, so I took the Angus from my A500 and put in in my A1500, low and behold the symptoms followed the Angus into the A1500, so I think I've found my culprit.

The Angus chip used is the fatter one (part 8372A) so if anybody has one (or even two) I'd be greatful.

 

[SpeedGeek]

@woodycool

I'm glad you found the problem!
It's always easier to try socket mounted chips than soldered in chips. You probably should start a "Wanted" thread for your Fat Agnus replacement unless Zetr0 can find one in his spare chip collection!

@Zetr0

LOL! Every one forgets that Fat Agnus is the Chip RAM controller. Denise is completely helpless when Fat Agnus gets lazy!

 

[woodycool]

Something I've always wanted to know: is it Angus or Agnus ?????
Either way, it's Fat and lazy!!!!

 

[mjnurney]

http://en.wikipedia.org/wiki/MOS_Technology_Agnus

Agnus my friend

Angus is a cow / a place in Scotland and I'm sure lots of other things

 

[woodycool]

This may well be quite embarrassing - after my PM to Keith I now expect he's going to come back to me with a fat cow rather than an Amiga custom chip! LOL