Dead A600 - And what's THAT??

[LuMan]

Well, my A600 finally turned up from eBay, but it's dead! In fairness the add did say it couldn't be tested, but was 'believed' to be working, so I contacted the seller to let them know. Anyhoo, I'm keeping the unit as the case is good and I want to try and revive it. Hopefully, you guys will have some ideas .

Symptoms:
When I turn on the miggy I get a white screen, but, instead of going to the 'insert disc' screen it just goes black (a green flash, about an inch high, pops up for a faction of a second a third of the way up the screen). I popped the ROM into my other A600 and it worked fine, so I'm pretty sure it's not that. I've also closely scrutinised the board for any obvious track errors, leaking, etc, but can't find anything obvious.

Both mobos are the same revision (1.5) and, aside of a couple of capacitors being made by different companies, seem identical, except for a mysterious component across the U12 chip. It could be a resistor, or it could be a capacitor. It could be something else, but even with glasses I can't make out the writing on it!! I'm tempted to remove it, but it's soldered on in a professional manner and thus looks to be 'proper'.

Attached pics show both motherboards and close-ups of the area with and without the strange component.

Any ideas..???

[kipper2k]

- does the floppy click once the a600 should have finished its initialization ?


- have you tried RF, composite and RGB video outputs ?

- caps lock blinking ?

- looked for broken traces under the rom chip socket ?


some a600 boards do have a capacitor across U12

[dabone]

Time to replace the caps!

Later,
dabone

[Hewitson]

Try another power supply if you haven't already.

[LuMan]

Thanks for the hints, guys. Had another look before coming to work this morning:

The FDD is shot, so I added my spare one. No click or pick-up or anything. Stuffed a disk in and still nothing.

No output from RF or composite.

No blinking Caps Lock light and no broken traces so far as I can see.

Tried an alternative PSU and had a prod about with my multi-meter. There's power to all headers and chips and across all the electrolytic caps (although this doesn't actually mean they're working, of course).

Next step is to replace the caps anyway and see what happens.

[kipper2k]

Originally Posted by LuMan

Thanks for the hints, guys. Had another look before coming to work this morning:

The FDD is shot, so I added my spare one. No click or pick-up or anything. Stuffed a disk in and still nothing.

No output from RF or composite.

No blinking Caps Lock light and no broken traces so far as I can see.

Tried an alternative PSU and had a prod about with my multi-meter. There's power to all headers and chips and across all the electrolytic caps (although this doesn't actually mean they're working, of course).

Next step is to replace the caps anyway and see what happens.

Depends how far you want to go with attempted repairs on this board. Take macro pictures of the motherboard as close up as possible (in as bright a light as possible) and check all resistors, smd caps, and especially the ferrite beads for a crack right across themselves. You cannot notice these cracks without a really good close up and i have found broken SMD's a few times using this method.

The next step for me after the visual check is replacing the caps and then to replace both CIA chips, the chips can still be bought at Vesalia last time i checked, however they are not socketed so there is a bit of work to be done here.

Another check you can try is to use a pencil, press down on various areas of the motherboard using a pencil with an eraser attached and then cycle the power, look for different symptoms.

[8bitbubsy]

Originally Posted by LuMan

[...] except for a mysterious component across the U12 chip. It could be a resistor, or it could be a capacitor. It could be something else, but even with glasses I can't make out the writing on it!! I'm tempted to remove it, but it's soldered on in a professional manner and thus looks to be 'proper'.

It's a cheramic capacitor, probably 0.01-0.1µF. I've seen them before.


It's connected to pin 1 (GND) and pin 13 (I REF on regulator circuit, whatever that one does...).
I guess it's a mod done on the newer A600 boards to get a more stable/better picture..?

[Khyron]

Originally Posted by LuMan

except for a mysterious component across the U12 chip. It could be a resistor, or it could be a capacitor. It could be something else, but even with glasses I can't make out the writing on it!! I'm tempted to remove it, but it's soldered on in a professional manner and thus looks to be 'proper'.

.01uF cap, and it was factory installed. Poor power routing on the composite out circuit, and when you have heavy pcmcia & floppy activity it would cause enough noise to make some TV's lose synch, the cap corrects this (well at least the sync part..)