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Bikerbob

800xl all ram bad??

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Hello all, I fixed my one 800xl for my friend - only 1 bad ram chip - lucky!

 

The other one the ram was heating up.. I tested the chips one by one in a known good working machine.. EACH ONE Failed to boot it.

 

Have you seen all 8 ram go bad without something else causing it?

 

I am afraid to put new ram in...

 

James

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Never had a machine where all RAM was bad that wasn't caused by using an incorrect power supply.  That being said, usually if I am replacing one chip, I'll do all 8.

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No the MT branded ram.. only one chip was bad in that machine.

 

its Mostek 4564-15.. 

 

All the personality chips are fine in the machine.. nothing else got hot. 

 

James

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If the power supply failed or if a c64 power supply was used then yes, I’d suspect all the ram to be fried plus mmu ( at the very least ). drams are quite sensitive to overvoltage and usually die instantly. 
 

remove all the ram first then check +5 voltages ( in case there’s still a shorted component somewhere ) before troubleshooting or swapping in new chips.

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When replacing the RAM chips, are the following chips acceptable replacements?

 

TMS4164-12 / MN4164-12 / HM4864P-2 

16-Pin Dip DRAM - brand new
64Kx1 bit DRAM

TMS4164 - Texas Instruments
MN4164 - Panasonic
HM4864 - Hitachi

Edited by pusakat
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YES, , one thing I would say and agree.. try and keep all 8 the same.. trying to mix chips does not mean they are bad, but might not work together.. my experience in this thread.

 

To those that were following.. 8 new ram chips in.. machine is good.. mmu was not an issue.

 

James

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If it is Freddie machine (C061991-29 - NCR, C061922 - CITEL ) - replace it, probably it is issue. Fault Freddie can damage all DRAM chips mounted in computer in future. 

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7 hours ago, pusakat said:

When replacing the RAM chips, are the following chips acceptable replacements?

 

TMS4164-12 / MN4164-12 / HM4864P-2 

16-Pin Dip DRAM - brand new
64Kx1 bit DRAM

TMS4164 - Texas Instruments
MN4164 - Panasonic
HM4864 - Hitachi

TI are my favourites but the speed is more important. Try to match the speed that you had in there before or install slightly faster ones. 120ns work fine 

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