HP-85A Dead

[juanjo_r]

Hello Folks!

i have a HP85A , and this not working. i check the voltages, and the bad are -5 volts
this drop to near 2 volts. also the i/o chip 1MA8 0101 and the cpu chip 1MB1 0101
goes very hot. y remove this chips and the voltages come to a good value of -4,98 volts. so i suspect as this two chip as bad.

anybody kown where i can get these chips? the ones in the board are ceramic with gold plate parts. i saw these chips in plastic carriers as udes in the hp85B is true this?

thanks in advance by the help , and sorry by mi very bad english.

jj

[cruff]

(12-07-2014 04:15 AM)juanjo_r Wrote:  anybody kown where i can get these chips? the ones in the board are ceramic with gold plate parts. i saw these chips in plastic carriers as udes in the hp85B is true this?

Did you try to determine if only one of the two chips is the culprit? Perhaps you only need one of them. At this time, probably the only way to acquire the needed chips is to locate another HP-85A. I found the CPU board by itself on Ebay some years ago, but have since given it to another person who needed the I/O chip. It may be possible that a dealer in older HP gear may have one. It can be hard, some times, to find a real dealer that has parts and not just listings of parts with no stock.

[juanjo_r]

hi Cruff. well I made a simple test, first I remove the i/o chip and measure the voltage and only a little change in -5volts. when I remove the CPU I observe the same behavior in -5 volt so I suspect the twos are bad!
also I don't have an idea how much those chips come warm so also today a make a test at -5Volts, and this consists in remove the chips and charge it with dummy loads to see if the PSU have a problem.
The most estrange is this machine running ok, but for a day to another not working anymore.

i not have the data sheet of those chips to see the normal heat generated, but the mine are really hot.

i can find a couple of online stores with these chips "refurbished" each near 50 bucks
so after the make a test of the psu testing i order the couples.

thanks for the repply!