Recent content by oldpcguy

I have a friend who runs an Apple rescue store and she has all kinds of Apple stuff (from the early Apple 8-bit to modern systems). People clearing out their basements, estate clearances, etc. Sometimes it has issues so she asks me to take a look at it. The board I was initially troubleshooting...

This afternoon I tried pushing down on the socketed (and non socketed) chips and did not observe any change in behavior by doing so. However while doing so the screen would occasionally change what was being displayed. Unfortunately it was doing so absent any pressure on the chips / board. Any...

Thanks for the suggestions, I'll give them a try over the weekend. @george I did suspect the power supply but it's the supply out of the working system. Unless there is something about the other board which may be causing stability issues. The IIc Plus is difficult to get information on. One...

I have an Apple IIc Plus system that I was given to troubleshoot. Initially the system powered on to a garbled display. I broke out the oscilloscope and started checking the normal things. The first issue I observed was the reset wasn't functioning correctly. It appeared UF17 was not functioning...

Seems reasonable to suspect the controller. You can also test for continuity between the following pins on the controller: P - Pin 10 (X3) and Pin 25 (Y3) ; - Pin 10 (X3) and Pin 27 (Y5) / - Pin 10 (X3) and Pin 29 (Y7) O - Pin 10 (X3) and Pin 31 (Y9) : - Pin 10 (X3) and Pin 22 (Y10)

Did you perform a reset of all the BIOS settings? Maybe there's a stale setting which is causing the issue. Maybe there was a problem with the update, have maybe try doing it again (if possible). What is curious is how the small (32MB and 256MB) CF cards aren't problematic too. Each is well...

To simulate a socked I stacked a second DRAM chip on top of the existing chips and then placed the floppy drive in place. There was sufficient clearance so my plan is to install sockets in order to use new, old stock memory chips for testing. If there is insufficient clearance with the sockets...

Removing the chips isn't difficult but it's something that I would rather not have to do if it can be avoided. I'd rather troubleshoot an issue rather than replace parts. Especially since replacing eight (or sixteen) chips would require eight replacement chips. That would work with one, maybe...

That it is. Sometimes the only answer is to remove the chips. Not a very difficult task but I like to put sockets in and certain chips in a IIc can't utilize sockets as they would raise the height of the chips too high.

This is good to know :) My memory test program uses 3 bytes of zero-page memory and 54 bytes a "regular" memory. It has to be hand typed into the ROM monitor. Before doing so I test the three zero-page locations by storing different bytes ($00, $FF, $55, $AA) into them and then reading the...

I am searching for a method which doesn't require me to do so as unsoldering 16 RAM (Apple IIc as an example) chips is not ideal for troubleshooting.

One of the most frequent failures I find in Apple II systems is that of a bad memory chip(s). In my years of doing this work I have not yet come across a good way to test memory. Sometimes it's easy to spot one with an oscilloscope, sometimes I can use the chip stacking method, and sometimes, if...

I am going to have to give this one some thought as it appears to be the same issue I am having with an Apple IIc Plus system. Just to confirm you're getting ~ .15 volts on IOU pin 15 when you have it in the socket which disconnects pin 15 from the system board? What are you using to measure with?

Using that configuration what is the voltage measurement on CPU pin 40?

It's certainly a possibility. Is this the result of running the self test?