Tek TDS784A CPU board dsyVGARamdacRegMemfailure [SOLVED]

[Jwalling]

Working on another TDS784A. CPU fails self test with:

Code: [Select]

"Sat 04-30-;6 02:46:21  ERROR: diagnostic test failure, dsyVGARamdacRegMem, table index= 1b8, actual data =  6 expected = 7, , failure in ramdacPalmem";""
"Sat 04-30-;6 03:10:05  ERROR: diagnostic test failure, dsyVGARamdacRegMem, table index= 1c9, actual data =  16 expected = 36, , failure in ramdacPalmem";"Sat 04-30-;6 03:28:56  ERROR: diagnostic test failure, dsyVGARamdacRegMem, table index= 214, actual data =  b expected = 2b, , failure in ramdacPalmem"
"Sat 04-30-;6 03:38:22  ERROR: diagnostic test failure, dsyVGARamdacRegMem, table index= 185, actual data =  1a expected = 3a, , failure in ramdacPalmem"
"Sat 04-30-;6 03:57:14  ERROR: diagnostic test failure, dsyVGARamdacRegMem, table index= 5, actual data =  32 expected = 3a, , failure in ramdacPalmem"

Failure turned out to be an Analog Devices ADV471KP35 RAMDAC on the CPU board in location U190, a 44 lead PLCC. I scavenged the chip from a TDS544A CPU board I had laying around.
Board now passes.

Jay

[nctnico]

Good job!
These kind of problems are hard to track down!

[Jwalling]

Good job!
These kind of problems are hard to track down!

Thanks. It'd be a LOT easier if Tektronix and Keysight/Agilent would give up the schematics for these old scopes like LECROY has done!  (Hint hint) if they read these boards. I know that Daniel from Keysight does; is there a Tek representative in the house? 

It's not like there could be much super-secret IP left in these units.

Jay

[casinada]

If I'm not mistaken Alan a.k.a "W2AEW" works for Tektronix. He might have some inside connections. Also the Tektronix Yahoo groups is another place with some ex Tektronix employees but it is dedicated mainly to the old glory days of analog scopes.