800XL RAMBO XL Failure

[hueyjones70]

I just bought an 800XL with a RAMBO 256K upgrade on EBay. When I first turned it on, everything seemed to be working and it booted up OK. I checked the ramdisk for memory and it showed only about 250 sectors available. I took it apart, saw no apparent problems and turned it on again and the computer booted to memory test and when it got to the end of the first row, the screen went black. I tried two more times with the same result. Star Raiders would boot OK. I tested all of the RAM chips and they were OK. Finally, I took out the RAMBO and the computer boots OK. I have to assume that the problem lies with one of the chips on the RAMBO board. Does anyone know of a likely suspect. The prospect of desoldering all or nearly all of those chips makes my head hurt.

[Greg I]

The first thing to check is the DIP connector between the main board and the RAMBO board. In my experience, that's where most of the problems originate.

[Kyle22]

Re-seat Socketed chips (if any). Check MMU C061618 and PIA C014795. Check ALL wiring connections to / from the RAMbo board.

If it is reliably flaky, then maybe look at C060472 Delay chip.

 

Look for cold solder joints everywhere. Use a magnifying glass.

 

You'll get it.

 

:)

 

[_The Doctor__]

use known good memory chip and known good support chips to piggy back one at a time the respective chip on the rambo... if the chip hasn't failed in a shorted way then the machine would/should start working

[hueyjones70]

I can't believe that I missed this initially, but one of the jumpers on the board was set incorrectly.