RAM selftest failed on Apple IIe

[blackswan]

Dear members,

having several problems with my Apple IIe, I finally was doing a selftest. Result:

RAM: F13 F12 F11 F10 F9 F8 F7 F6

My RAM looks like:



On the photo you can see, that most of the RAM chips are MT4264-20. Only the chip on column 6 is a Fujitsu MB8264-20 (in a socket). Seems like this chip has been changed already. Does anyone have an idea what's wrong here?

Cheers,

Blackswan

 

[techknight]

I just happened to browse through your photos, and noticed your IIe monitor has a horizontal line.

Thats because your vertical deflection output circuitry needs attention.

 

[blackswan]

I just happened to browse through your photos, and noticed your IIe monitor has a horizontal line.
Thats because your vertical deflection output circuitry needs attention.

Thanks for your comment on this. I already sold the broken monitor, because I was lacking tools and knowledge about the TDA1170N to repair the non-working vertical deflection of the A2M2010P.

Any ideas about my RAM problem?

Cheers,

Blackswan

 

[Sebastian]

I'm not knowledgeable about IIe's, but my reasoning is that if a lot of chips seem to fail, it's probably a fault in the adress-mux, the Row adress strobe or the Column adress strobe.

 

[techknight]

Especially if the failure reports a pattern. Hypothetically speaking if its every 3 bytes or so, it reports a failure. If its an even-divisible error then it can be the controller/muxes. But if the failure is totally random and makes no pattern at all, its the RAM IC.