Dead A590 board, help needed.

[kokkiklhs]

Hi folks!
I recently acquired 2 A590 hard drives, the one is perfectly working (still with its original WD 20MB XT harddisk!!) but the other one does not want to cooperate!

Well, the description of the problem:
The faulty 590 powers up with its own PSU, power LED comes alive, the disk spins and the activity LED blinks for a while, the fan is spinning... BUT the Amiga itself does not power up, with or without the hard drive attached on the 590 PCB, with or without extra memory installed! Always exactly the same result:
The caps lock LED flashes for one second (as it should) but then there's no reset on the Amiga side and both Amiga LEDs (power/floppy) stay permanently off. The screen is totally black with no signs of a reset/init attempt.

What I have done so far:
It's been one whole day that I am trying to figure out the problem.
-Cleaned the connector contacts, anyway they seemed in perfect shape even before. Checked the soldering joints (and on power input), they seem to be perfect. Measured continuity for the POWER SENSE signal from the PSU plug to the connector PIN6 and the RESET signal from IC10 pin2 to the connector pin 53, they're OK. Also measured 5V and 12V currents from the PSU input towards the circuit, they flow without problem.
-Swapped each and every one of the socketed ICs, they all (fortunately) work with the good board, also the chips from the working board give exactly the same bad result (as described above) when installed to the faulty board. Cleaned all the socket contacts with contact spray, no improvement.
Anyway, both 590 boards are physically in excellent shape, clean and intact without signs of corrosion or nasty operations of the previous owners... so I am stuck for now...

I am using the same Amiga (rev5/1.3/512k) and the same PSUs (A500 and A590) for my testing on both boards.
I supspect that the next candidates are all the logic 74LSxxx ICs that are directly soldered on the board. After leaving the board switched on for several minutes, I didn't notice excessive temperature on any of them, they run pretty cool.
Well, before I start butchering without a clue, I need your opinions.
Has anybody experienced a similar problem?
TIA for any help/suggestions!!

 

[BLTCON0]

I'd just check the chips, they aren't that many. Other than that, schematics for the A590 do exist IIRC. And you could consult the Autoconfig section in the hardware manual for ideas on testing if the card gets stuck up somewhere (and where) in the process.

 

[kokkiklhs]

I'd just check the chips, they aren't that many. Other than that, schematics for the A590 do exist IIRC. And you could consult the Autoconfig section in the hardware manual for ideas on testing if the card gets stuck up somewhere (and where) in the process.

Thanks for the suggestions! I already have the schematics, that's why I suspect U10, but the bad thing is that I don't have an oscilloscope (or a spare IC) here, and I am trying to avoid desoldering from the good board...

 

[BLTCON0]

Well, a single test you can try is remove the ROMs and use a binddrivers version.
If it comes to life, you'll know it somehow doesn't read the ROM.

 

[kokkiklhs]

Well, a single test you can try is remove the ROMs and use a binddrivers version.
If it comes to life, you'll know it somehow doesn't read the ROM.

It always does the same thing, even with ROMs detached, and all socketed ICs detached... it doesn't along the Amiga to start.
The power LED on the computer stays permanently off, even though the HD controller and disk seem to start normally, with the whole init process regularly done...
Thank you for your ideas my friend, anyway!!