512K hardware expansion debugging?

[oracle_jedi]

Does anyone have any brilliant insights on how to diagnose a faulty 512K memory expansion?

 

I have a DRAM piggy-back expansion. The base 256K seems to work fine, the additional 256K is reported "E" by SRAM021.

 

I rigged up a 9V battery to a buzzer and probed the 128 legs of the DRAMs, and got a buzz from everyone, so does that mean they are all soldered? Or is it shorting through the chip?

 

To test I would touch one lead Pin X of the first chip, and then the second lead to the same pin of chips 2, 3 and so on until I got to chip 8.

 

Anyone got any clever methods? Or am I down to removing each of the extra 8 chips and eye-balling it?

 

Thanks

[+bob1200xl]

9 volts is way too much to apply to the chips. You'll blow the chips with that much voltage. You can blow the chips with a lot less, too. Never apply an external voltage to any chip in the motherboard. If you want to check continuity, use a good ohmmeter. (which applies a voltage to the chip... I know)

 

In general, upgraded or not, you are pretty much limited to swapping chips and inspection. Or, you need tools for the job. In some cases, you can find the bad DRAM chip just by feeling the chips while they are running. The hot one is bad.

 

Since the system runs the lower 256K, can you just write a little handloop to write/read from the upper 256K? Look to see what the problem is? All $FF, one bit missing, duplicate addresses?

 

Bob

 

 

 

Does anyone have any brilliant insights on how to diagnose a faulty 512K memory expansion?

 

I have a DRAM piggy-back expansion. The base 256K seems to work fine, the additional 256K is reported "E" by SRAM021.

 

I rigged up a 9V battery to a buzzer and probed the 128 legs of the DRAMs, and got a buzz from everyone, so does that mean they are all soldered? Or is it shorting through the chip?

 

To test I would touch one lead Pin X of the first chip, and then the second lead to the same pin of chips 2, 3 and so on until I got to chip 8.

 

Anyone got any clever methods? Or am I down to removing each of the extra 8 chips and eye-balling it?

 

Thanks