Emax

a logic anyliser is the only way you will know for sure which ic is bad

either get a pc usb software 1 about £100

or a proper hardware 1 £600-1000 depending on brand and specs

but first test all power lines 5v to the chips and make sure that there is no cold spots solder joints check you have continuity with all 0v lines as well as it could be a 0v fualt 

put your tester on the 0v pin of the ic and then put hte other probe on the chassie or earth location on the psu and use the continuity sounder to identifie if you have 0v

and do the same on the 5v line from the psu to all 5v pins on the memory ic

!!!!!!this test should be done with the unit disconnected from the mains socket no power???!!!! a little warning message

you will no if it is a cold solder joint that way test the pins on the ic not the circuit board

reflow all solder joints on the the memory pcb upgrade board

if having the same problem then you know it is 1 chip

then you will need to go to the logic anyliser route

otherwise its a guesing game this would be a good time to fit sockets first get some replacement chips desolder the first 1 add socket then fit new chip to this socket

if problem still persists then put old chip back in and desolder the next and so on and so on this is the long way round but if you have not got a logic anyliser than its the only way

you need a good desoldering station for this and also some desolder wick to finish clean the solder pads you will also need to desolder all chips if going to put back


  ----- Original Message ----- 
  From: Adam 
  To: emax@yahoogroups.com 
  Sent: Tuesday, September 27, 2011 11:15 PM
  Subject: [emax] How to determine which DRAM chip fails in EMAX II?


    
  We know how to start the memory diagnostics. The service manual describes the process, but does not give a good spec on how to determine which IC is bad.

  Eg. i have a 4Meg Emax that fails the memory test. I swapped the pals (seems that the 8Meg rack's pals are the same as the 4meg keyboard), so it's the chip(s).

  error is like: address: 100,002 is: 7225 sb: 8225
  now, it is obvious which bit fails. but it still does not tell which IC is bad, unless you know this address 100,002 was composed! 

  ANYONE KNOWS THIS?

  (swapping the chips is not possible, as they are soldered into the PCB.)

  thanks!



  


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