Amiga 2000 Boot Sequence Q

[bozimmerman]

Hello all.  I have an A2000 (B2000 CR 4.4) that isn't booting.

I've tried to do my due diligence, but the information I've found has been ambiguous to me.

When I start the computer, the screen goes from black to bright blue for perhaps a second, then to either black or dark grey (how can I tell?) and stays that way.  The caps-lock light never does anything.

Does the Blue Flash mean it's having problems with the custom chipset, or is that only if it stays Blue?  If the former, well, what exactly *is* the custom chipset.  Isn't every MOS/CSG chip *custom*?

- Bo

[bozimmerman]

Obvious first question, have you removed the battery?  Any motherboard damage?  Also have you reseated all the custom chips?

Hello Mr. Mike,

Yes to the battery, no serious mb damage I can see but I'm still evaluating that, and yes I've reseated them all.  It seems you might know the answer to one of my questions, namely, what is a "custom chip"? Am I right that anything with the MOS/CSG moniker is a custom chip?

- Bo

P.S. Great flying mexican squirrels! You have an A2k w/ 136mb and an 060?! Gratz!

[bozimmerman]

Loots like I had more spares than I thought.  I swapped the CPU, CIAs, Kickstart, Gary, Agnus (an 8370 for the 8371), Paula and Denise.  Of course, I can't speak to whether the spares were also dead, but I took my chances. (This is an A1500, btw, but it had an upgraded Denise .. the 8373!

I also discovered that the reason my keyboard light did not come on was because the keyboard light in that keyboard was dead. Everything else about it was fine. :/

Under the cpu actually looks better than the areas to either side of it, which have a bit of the grunge from the battery leak.  The underside of the board is entirely pristine.

My next job will be to measure resisters, put some capacitors in the problem area on order for replacement, and use the R6 schematic, as best I can, to check all the traces coming out of the cpu.

Any other advice is welcome. Desperately welcome, in fact.  I'm still especially interested in the significance of the one second blue-screen flash.  Should I take that seriously?

I would look carefully around the battery area, especially around & under the CPU socket area.

But I'd start with every socketed chip - press down firmly on them, inspect their pins, etc.  Also what version ROM do you have in here?  Do you have a spare you could swap in?  A bit scatter-brained today, just thinking out-loud of other common problems.  When was the last time this system worked?  Have you tried with any/all expansion cards removed and devices disconnected?

Edit: this link has lots of info on Amiga custom chips:  https://en.wikipedia.org/wiki/Original_Chip_Set
and this one:  https://en.wikipedia.org/wiki/Amiga_custom_chips

[bozimmerman]

Hi Mike,

The power supply was the first thing I checked, but I'll check it again.  I've reseated AND swapped every chip on the board with spares multiple times, but I'll do that again too.  Because why not? Nothing else is working!

Tonight I checked the address (up to A18 or so) and all the data pins on the CPU up to some 245's and the kickstart.  Despite the socket looking a little grungy, continuity looked good.  I'll hunt down the rest of the pins from the schematic, but I have to do it in short bursts.  My hardware troubleshooting patience is low.

An important question:

I have the board out with power supply and video and nothing else.  I should still expect an insert Kickstart Disk screen, right?

All this time I have been assuming that.

- Bo

P.S. If you are ever in the Austin/Round Rock area, stop by!

Bo,
   Start with the power supply, take a multimeter and check voltages at the motherboard connector.
just in case you lost the tick signal,you might change the jumper to get tick from video.
Don't just push down on chips, this is useless, pop each and inspect it and the socket for tarnished/bent pins. reinstall the chips.

I have spare s871,8372a agnus if you need one, I am in texas, so shipping would be quick(i think you were also in texas). just Pm me here if you want it.

Mike

[bozimmerman]

Hmm.. thanks for those links.  The crystal is certainly something I haven't looked at yet, and I still need to finish going through all the cpu pins for continuity.  The acid damage did hit the cpu area, but not very hard.  Still, it's my best bet.

So, something weird just happened.  I positioned myself to do some power measurements and turned it on, expecting nothing.  It's the 4000th time I've turned it on: black screen, flash blue, back to black forever.  However, this time, I got a 2.0 roms boot disk screen.  I stared in wonder.  It lasted about 10 seconds and then gurued.  I restarted it again, and this time it just instantly gurued.  First signs of any life at all I've seen.



This will inspire me to double my efforts.

- Bo

P.S. Yes, this board has value beyond function for me.  But even if it didn't, sometimes a motherboard repair is not about the repaired motherboard, and more about the repairing.  I've learned a bundle just asking questions here and trying to follow through.

[bozimmerman]

Fixed.  Thanks everyone for your awesome advice!