Quick question about 64K upgrade for 600XL

[jowi]

I just did the modification on my 600XL for upgrading to 64Kb. Lifted the resistor and the pins on the various ic's, connected it the way it should etc. I bought 2 NEC D41464C-10 chips, but either these are the wrong ones, or they are broken... on close examination, some pins were bent, looks like they were pulled by force from some old board. So when i turned the 600XL on, nothing happened... i could also not force a selftest. No response.

 

So i've replaced both chip with the original TMS4416-15 and rebooted. This time without keyboard, and to my surprise the memory selftest started by itself... is that correct? I had no keyboard plugged in?

Naturally the test failed when it passed the 16Kb. But i did not expect it to do a memorytest by itself?

[Rybags]

You can actually test the higher capacity Rams before starting the mod part of the upgrade - the system will only see the first 16K.

 

By doing the mod to the motherboard you're enabling the full 8 rows+columns of access to the Rams rather than the default 7 rows+cols. Which means that with 16K Rams they'll have mirror images appear 3 extra times in the memory map.

The OS doesn't know that it's the same memory appearing multiple times so will just assume you have 40 or 48K present.

I'm surprised it even gets to the self-test. The powerup sequence would overwrite and clear all of zero page once it gets past 16K - I suppose it probably inadvertantly flags a memory failure then drops into self-test.

I guess from there it probably tries to run the memory test and would likely crash at some further point.

[jowi]

I tested the 64K in the other machine, also dead...

So i have to wait for new chips to arrive.

Edited November 18, 2018 by jowi

[manterola]

I suggest this modification , because you can go back to stock 600xl since it requires no change to the PCB. It is just soldering 2 wires and placing 1 jumper. Just my 2¢

[jowi]

The mod is already done, using the lift-the-resistor method. I don't like the jumper part of the above mod.

The resistor mod can be undone as well, just re-insert the resistor, remove the wires and bend the legs of chips back. The latter is something you have to do as well with the 'jumper' mod.

Edited November 18, 2018 by jowi

[_The Doctor__]

while a picture is worth some words... it does not say which legs are lifted or just soldered to. be mindful there was a bad mod in one of the threads... the good mod thread mentions the bad mod and to use the good one or some such blah blah blah

Edited November 18, 2018 by _The Doctor__

[jowi]

I did this mod:

Edited November 18, 2018 by jowi

[Paul Westphal]

Get new 41464 rams and do this mod. Those are holes on the PBI 16 and 17.

[jowi]

That's the same mod There are multiple ways of doing this, any method will do and in the end does exactly the same, they just differ in how you want to disable U18 or where you pick up A14 and A15.

Edited November 18, 2018 by jowi

[jowi]

Finally got the chips from alixpress... put them in, booted, nice prompt in stead of a memory test

The memory test itself when forced is ok as well. Now i can finally reassemble it and start playing!

[xrbrevin]

great success!