Atari 130 XE Ram Problems

[philgood1351fr]

Hi, checked what have already been discussed here with no luck so I ask you my friends for advices....

 

My 130 XE always boots on Memory test. the 2 ROMS are OK, but RAM is all red except 4. Unsoldered the 8 chips, put supports then tried with differents chips according to what I read here in past topics.

Tried with KM 4164-B-10, TMM 41256AP-12, TMS4164-20NL chips but no luck (same results on tests).

Diodes are all ok (5v).

Tried to swap 1st 64 bank with 2nd 64 bank by crossing resistors R110 and R111 but black screen.

 

Anyone can help on this ? Are my replacement chips are the good ones ?

 

I checked the MT4264 voltage, and notice that I have 5v on some pins and 3.6 on some other. Even 1 pin (pin 3 or 4 that have 1.9 and this one has a dropping voltage during the Ram test). Anyone have the correct voltage for each memory pin ?

 

Thanks for your advices.

Phil

Edited September 22, 2021 by philgood1351fr

[TGB1718]

The only pin guaranteed to have +5V on it is pin 8, the power supply pin,

all the others are switching on and off at different speeds hence the varying voltages you are seeing.

 

You will not be able to measure voltages on any of these pins with a voltmeter, you need a scope.

 

Could be an MMU problem or Freddie chip

 

Edited September 22, 2021 by TGB1718

[xrbrevin]

yes im thinking freddie too

[philgood1351fr]

ok thanks a lot.

I suppose it's the same chip on the 800XL ? If so I'll be able to switch as I have 3 Atari 800.

Thanks a lot for the tips.

Phil

[xrbrevin]

only the very late 800XLs were made using the Freddie chip, then all the XEs

[Beeblebrox]

@philgood1351fr

You can get a new Freddie chip here:https://www.ebay.co.uk/itm/124704063542

 

Also BTW I got me one of these DRAM testers which has proved most useful for checking all my 16pin DRAM chips  (right socket):

 

https://www.ebay.co.uk/itm/124726020732

Edited September 23, 2021 by Beeblebrox

[Beeblebrox]

1 hour ago, xrbrevin said:

only the very late 800XLs were made using the Freddie chip, then all the XEs

Yup, far as I am aware only the Atari 800XLF boards and then XE models have s Freddie chip.

[philgood1351fr]

Right. Thanks.

I bought the DRAM tester and the Freddie Chip.

++

 

[Beeblebrox]

4 hours ago, philgood1351fr said:

Right. Thanks.

I bought the DRAM tester and the Freddie Chip.

++

 

@philgood1351frCool. Make sure with the DRAM tester (if you bought the one I linked to above), that you read the instructions and test DRAMs the right hand socket. If you put them in the left one you can fry the likes of 4164 and 4264 chips, etc. I taped over the left socket to stop any accidental usage. (Just don't trust myself). The only instructions you get on that Ebay link is in the listings - they don't include them with the unit.

 

Great re Freddie chip. 

 

good luck

[philgood1351fr]

Yes, I printed the manual on Ebay. And I saw the difference between left and right test pins.

Pretty sure I'll put a blank scotch over the left one too as I mainly tests 5v chips....

here is the complete manual if needed.

 

Thanks. 

DRAM_Tester_UserGuide.pdf

Edited September 23, 2021 by philgood1351fr