XEGS Fails RAM Test

[Officepot]

I recently acquired a XEGS that passes all tests besides the 3rd and forth row of RAM tests. Are these RAM chips easy to come by? Figure I can determine which RAM chip is bad and replace it. The console only boots directly to the self test. I am assuming the bad RAM is the reason it will do nothing other than boot to the self test. Any help is appreciated!

[Peri Noid]

An XEGS has 2 RAM chips of a 4464 type (4x64Kbit). They are easy to find.

[xrbrevin]

bad ram operations will make it boot to self test

replacement RAM chips are obtainable and you can piggy-back them to determine the faulty one(s)

here is the schematic set

 

xegs.zip

Edited October 16, 2023 by xrbrevin

[Beeblebrox]

@OfficepotRemember the xegs isn't socketed so order 2 x 18pin double wipe sockets at the same time and take real care when removing the old chips from the pcb.

Edited October 16, 2023 by Beeblebrox

[Officepot]

I read that this board is very easy to pull up trace lines... I will be as careful as one can be. Thanks for the help on determining this is why it boots to self test.

[Beeblebrox]

59 minutes ago, Officepot said:

I read that this board is very easy to pull up trace lines... I will be as careful as one can be. Thanks for the help on determining this is why it boots to self test.

Yup. The Xegs pcb is slightly better build quality than the main XE line, but still not as robust as the XLs.

 

I've upgraded two xegs's recently (replacement ram and and socketed os and MMU for u1mb, plus the 74ls08 socket to swap for a 74f08 replacement. So long as you clear all the solder and don't force the chips off the board if there is notable resistance you should be OK. 

 

Remember also to make sure it's all clean both sides of the board before putting the sockets in. Also make sure the sockets are flush. 

There may well be a slim chance their are also other issues which you might find after fixing the ram, but fingers crossed it's straightforward. 

 

Edit: also bear in mind if you do find other issues and these are with the os or MMU chips, the xegs doesn't use the same os or MMU chips as the other XE line, ( or the 600/800xl). It has it's own custom ones. 

 

 

Edited October 16, 2023 by Beeblebrox