Amiga 3000/16mhz woes...

[Ilwrath]

I was going through my Amiga inventory and sorting out some odds and ends to sell off, when I met back up with an Amiga 3000 that had perplexed me enough that I shelved it.  

Here's the rig-
It's a 16mhz Rev 9 A3000 desktop.  
Standard configuration, with the exception of 3.1 ROMS (ver 40.68)  

Here's what it does-
Turn on the power...  
HD spins up normally.
Power light comes on at normal low-brightness level.
no HD light activity.  
Keyboard caps lock flashes one, video outputs a black screen.  
CTRL-Amiga-Amiga sends a reset to the HD (you can hear the HD make the same click as when it first spins up) and the keyboard caps lock flashes once again.  Video never changes from the stable black screen.

Here's what I've checked-
Confirmed all jumpers set to 16mhz INTERNAL clock for both mainboard and CPU.
Set ROM speed jumper to slower access, in case system was unable to read ROMS. -- no change
Swapped ROMS for an A3000 set of 2.04 ROMS -- no change.
Removed fast mem -- no change.
Reseated all chips -- no change.

I'm stumped.  I'm used to getting some kind of screen activity or hint as to what's wrong....  Any ideas, suggestions, folks?

[redrumloa]

reseat all socketed chips and try the following method.

Disconnect all hard drives, floppy drives and remove all expansion cards. Turn the computer on and wait several minutes. You should at least get the KS3.1 requestor. If you don't get this requestor than something is going on..

[Castellen]

Does the LED turn on and off when you press caps lock?  If so it indicates that there is some CPU activity.

Does the power LED change between 2 brightness levels just after power up?  This is in the computer's power up sequence.
Sounds like it's running through the power up sequence, so there could be a problem with the CPU itself, or any of the custom logic like Gary.

As suggested, reseat all socketed devices first.

One of the programable logic devices U202, U203, U701, U714 could also be faulty.

One of the small fuses could be open circuit if something has been plugged in incorrectly.


Could be any number of things really.  You're possibly a bit stuck without access to known working spare parts and some test equipment.

[Ilwrath]

Does the LED turn on and off when you press caps lock? If so it indicates that there is some CPU activity.

It will for about the first 5 seconds, or so.  Then it'll stay off.  Almost like the system hangs VERY early on.

Does the power LED change between 2 brightness levels just after power up? This is in the computer's power up sequence.

No, comes on on the dim setting, stays dim.  never flashes bright.

Sounds like it's running through the power up sequence, so there could be a problem with the CPU itself, or any of the custom logic like Gary.

Yeah... This one was my fear.  I'm wondering if I should try a CPU card in the fast slot to try to bring the system up.  Does an A3000 still need the system CPU if it has a CPU card in the fast slot?

As suggested, reseat all socketed devices first.

(already did.  thought I wrote that in the already tried column.  Far from my first miggy I've torn up.  ;-)  )

You're possibly a bit stuck without access to known working spare parts and some test equipment.

Also my fear.  Thanks, though.  :-)

[Ilwrath]

One of the programable logic devices U202, U203, U701, U714 could also be faulty.

Hmm......  Quick test with the accurate measuring tool of my fingertip.....  U714 is warmer than the others.  ;-)

Where would I locate a new U714, nowadays?  Red?  :-)

[redrumloa]

Where would I locate a new U714, nowadays?  Red?  :-)

Probably not but i can check. IIRC U717 is the location on the MB right? What is the actual chip part number?

[Ilwrath]

I have a 390529-03 -- it's printed on a silver C= sticker.

I doubt that part is on an A500... I was going to check my part-scavenged machine, but it's in the back of the closet, and I haven't gotten to it, yet.

[redrumloa]

Naah don't have it. I have a bunch of old custom chips, but i don't have that... sorry..

[Castellen]

@llwrath:

It's normal for U714 to get fairly warm.

If you're worried about it (they can fail) then you can get these wee self adhesive heatsinks for DIL package ICs, which could help.

These ICs are only used in the A3000, not in any other models (maybe in A2000???)
The good news is you can still buy the part.
The bad news is it's programmable logic.
The good news is I think I have the JEDEC files to program them somewhere... I think...
The bad news is you'll need a programmer, though I have one at work.

If you replace the PAL device with a GAL equivalent, they would probably run a bit more efficient, I.E. cooler.

I also have a few A3000 original spares too, including U714, in working condition.

[Castellen]

Forgot to add, could be a CPU problem with your A3000, hard to say.  To be honest, it could be any number of things.

Not sure if a CPU card will run without the onboard CPU running or not?  Never tried it.

If you have an spare A3630 or A3640 (rev 3.1), chuck it in and see what happens :-)


Other than that, it's time to break out the logic analyser and the digital storage scope!