Trashpicked Apple IIe - vertical bars on screen and graphical glitches

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Trashpicked Apple IIe - vertical bars on screen and graphical glitches

Several weeks ago, I found an Apple IIe lying in a pile of trash and broken furniture on the curb a few miles from home. I took it home and completely disassembled and cleaned everything, and replaced the RIFA filter cap in the power supply just to be sure. Other than the keyboard, everything seemed to be in good shape, although there was some corrosion on sockets and internal connectors.

When I powered it up everything seemed to be working properly for a few hours. Then, it started to develop graphical glitches. In normal text mode, I sometimes see white bars creeping down the screen, solid at the top and intermittent at the lower part of the screen. These are intermittent and normally not present. In color mode, when playing games, I see black bars on the screen, although they only seem to affect some colors.

RAM test succeeds, so I am suspecting the problem lies in the video ROM or something connected to it.

I removed and cleaned all the chips and sockets and re-seated everything. This fixed the problem for a few minutes before it returned.

Any thing else I should check before I start ordering replacement parts?

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My spidey sense is telling me

My spidey sense is telling me the resistor pack RP3 next to the Video ROM may be hosed, or the LS166 shift register.

RP3 should have 3.3k ohm between pin 1 and each other pin. The IOU might also be the culprit.

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The resistor pack is reading

The resistor pack is reading about 3.2-3.3K between all the other pins and the common, so I don't think that's the problem. I may need to borrow an oscilloscope from work to look at the 8 lines between the ROM and the shift register to see how they look. Though the shift register is a cheap enough replacement part that I could just swap it and see if that makes a difference.

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A very good troubleshooting resource...

What a great trash pile find, and it looks to be in very good physical condition for a first generation IIe.  I've always preferred the white keycaps myself.

Check out this link for troubleshooting screen/memory anomolies:  https://ct6502.org/home/assemblylinesplaylist/

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After some further testing, I

After some further testing, I'm pretty sure the problem is in the Video ROM chip. The data coming out on D5 and D6 is garbled and visibly difts as the chip warms up. It doesn't look like I can just order a new vintage video ROM by itself, so I'm probably going to have to get the full IIe Enchanced upgrade kit from ReactiveMicro.

I'm also finding that several of the keys on the keybad are really sticky and don't come back up well after being pressed. I'm going to try again to clean those, but failing that, does anyone know of a source of acceptable replacement buttons?

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ellindsey wrote:I'm probably
ellindsey wrote:

I'm probably going to have to get the full IIe Enchanced upgrade kit from ReactiveMicro.

 

 Might want to also look at the ROMXe from ReActiveMicro. Replaces the video ROM with up to 32 fonts and gives you choices for System ROM as well. Oh, and a Real Time Clock to boot!

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Replacing the ROMs and CPU

Replacing the ROMs and CPU with the parts provided in the enhancement kit completely fixed the video problem, and also seem to have fixed some general reliability issues. I had been having real problems getting it to reliably load software from a simulated vidoe cassette file, but now that's working every try. The only remaining issue on this machine is several sticky keys on the keyboard. Does anyone know of a source of replacement keyswitches for an Apple IIe keyboard?

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If you do a search on ebay

If you do a search on ebay for Apple iie key swicthes you will find quite a few options.

You need to determine if you need the stem colored 'cream' or 'black'.

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