2000 - black screen... Chips good... PSU good...

[chiark]

well, here's one to keep me challenged!

I got a known faulty 2000. It's in good condition cosmetically, but fails to do a thing.

The psu gives the right power
I've swapped every socketed chip with a known good machine. the known good machine works with the duff machines chips. The duff machine doesn't work with the good machine's chips.

Keyboard, when plugged in, doesn't give any errors: caps lock lights then goes out. Caps lock then turns on and off, which I think means that the processor is working (68000 as opposed to keyboard)?

The CPU is getting 5v between pins 14 and 16.

Jumpers are all identical, and right.

Only strange thing is that U541 and 540 are soldered into some sort of upside down daughtercard... I think these are just octal latches so shouldn't cause problems like this. Maybe. but I really don't know.

Strangely, F1 has been replaced with a socketed fuse which suggests something somewhere may have drawn too much current, but there's still 5v going to that. Hm....

Any ideas where to start on this one?

[chiark]

Hmmm f5 shows no continuity.
Time for a schematic!

[musashi5150]

I can't really offer you any help on this chiark, but I'm interested and wish you luck

[chiark]

replaced f5. no joy...


cheers musashi. I think i need luck on this one!

[TheCorfiot]

@chiark

The keyboard Caps LED flash does not prove that the 68000 is running only that the Keyboard MPU has initialised.

3 suggestions

Swap X1 or use frequency analyser to ensure the 68000 is receiving it's clock, I also presume that you have tried swapping the 68000 (does it get hot?).

What rev is your Motherboard does it contain a Buster IC, If so check BBoAH as certain revisions req a Buster Tower to correct a bug in the Buster Logic which is not required for later revisions.

Contact issues on AGNUS can also cause a Black Screen

The Tick signal is also setup correctly.

Good luck my friend & let us know.

TC

[chiark]

Thanks TC, I've swapped the 68000 as one of the chip swap... No beans. I've got a simple frequency analyser on my multimeter, so I'll try that. Not checked/swapped X1 - good point! If that's not running, sod all will work!

It's a 6.2 I think, and it had the same buster as my working machine.

Agnus socket is perfect on the knackered machine, and slightly cracked on the known good machine .

Tick is coming out the PSU correctly, unfortunately, and is jumpered to use the PSU rather than vsync (or whatever the other option is)

I'm off to bed now (yeah, I know, lightweight!) but I'll give this another try tomorrow.

I still find it strange that F5 was blown, as that's near the video output, but I guess it's protecting the power found on the video out connector...

[TheCorfiot]

@chiark

If F5 is blown your A520 wont work properly but I guess you are either using RGB or the mono video port whilst repairing the A2000

And yes rev 6.2 does not need the Buster fix and as you have already swapped & proved the chip is OK, then the problem is not buster...

Will keep thinking about this one for you.

TC

[rkauer]

Sometimes the TTL flip-flop right over the CPU go busted. But in this case the 2000 will be put an reboot state (dark-grey, light-grey, white, reboot).

Check the Agnus and CPU sockets for oxidizations. Then look around the battery area. Also check the crystal and nearby traces.

BTW: blown F5 means just the +12V on video port had a bad time. Normal when people hangs a scandoubler or an A520 behind the Amiga and unadvertisely "bumps" on the Amiga when she is on, causing F5 to blow up and the external device to wreck (A520, mostly).

[chiark]

Thanks TC & rkauer
I'm using a 1942 monitor with it, so using RGB. Floppy drive doesn't seek either, unfortunatey, and power light stays at one illumination level.

Thanks for the info on f5. It was a false hope, but what has got me wondering is the hack that's been done on F1. Strange.

I've got a fairly nasty portable scope that I'll check everything out with tonight.

Thanks for the advice and encouragement!

[chiark]

Cpu is getting 7.09MHz, as is gary - and gary's also getting the 3.55MHz signals too. Damn. I'll have another check for oxidation and crap, as there has been a battery leak in the past but it doesn't appear too bad.

Thanks

[X-ray]

"Only strange thing is that U541 and 540 are soldered into some sort of upside down daughtercard... I think these are just octal latches so shouldn't cause problems like this. Maybe. but I really don't know."
------------------------------------------------------------------------------------

My old B2000 had that also.
Sorry, I can't help though, because that was some time ago and I don't have it anymore.

[cosmicfrog]

wheres the , can we have picces plz

[chiark]

it's a 2000 motherboard. What more is there to say?
But yeah, I'll take photos

[chiark]

Some 'wit has completely butchered the lines under the kickstart chip to the point that there's one track damaged. I think this could be not helping...

[TheCorfiot]

Originally Posted by chiark

Some 'wit has completely butchered the lines under the kickstart chip to the point that there's one track damaged. I think this could be not helping...

Hey mate I hope that's easily repairable, with a bit of luck that maybe the problem.

Keep us posted

TC

[chiark]

Well, three tracks to the kickstart chip are butchered, so I'm guessing that'd stop a machine completely in its tracks!

Socket now removed, damage cleaned, and board prepped .... Watch this space

[X-ray]

Yes, three tracks damaged is the medical equivalent of a recto-vaginal fistula with a purulent exudate.
May the surgery be successful, Dr Chiark!

[TheCorfiot]

Originally Posted by X-ray

Yes, three tracks damaged is the medical equivalent of a recto-vaginal fistula with a purulent exudate.
May the surgery be successful, Dr Chiark!

F*****g Awesome analogy

[chiark]

Thank you so much for painting pictures with words .

Fixed those three tracks, replaced socket.

Now got a yellow or green screen (can't quite tell which...)

Progress!

[TheCorfiot]

chiark,

Check Agnus is seated correctly, reseat if necessary. Good news is the system is now going through it's POST.

No instant Red means that the KS ROM is being read OK & the checksum has passed. your rework has been successfull.

Yellow indicates memory issue.... remove any memory expansions if present.

yellow / green which I have had before have been cured by re seating Agnus.

Getting there bit by bit.....

TC