Tektronix TDS754D diagnostic test failure, dsp68kInMemTest

[wukiduki]

hello!
Recently got a tds754d oscilloscope, the function looks normal, but the processor self-test cannot pass.
 I have cleaned the PCB, the problem still exists.
 Does anyone know which chip is related to this error?
 Need some help.

ERROR Log read via gpib：

Code: [Select]

THU JUN 07 13:06:34 2018  ERROR: diagnostic test failure, dsp68kInMemTest,
** addr = 0x7028200  exp data = 0x55555500  actual = 0xff555500,
** addr = 0x7028204  exp data = 0x55555500  actual = 0xff555500,
** addr = 0x7028208  exp data = 0x55555500  actual = 0xff555500,
** addr = 0x702820c  exp data = 0x55555500  actual = 0xff555500,
** addr = 0x7028210  exp data = 0x55555500  actual = 0xff555500,
** addr = 0x7028214  exp data = 0x55555500  actual = 0xff555500,
** addr = 0x7028218  exp data = 0x55555500  actual = 0xff555500

[Haatveit]

It could be a bad assumption, but since all the addresses tested get the same bit pattern wrong, I might suspect some memory address PCB traces could be corroded? I know that was a problem of many of these scopes. Electrolytic capacitors leaking and the following corrosion on the board itself.

[madao]

Old questition, i know, but  it may be helpful for other people with search word "dsp68kInMemTest"

But, i want tell about this ERROR.

I got a TDS754C from israelite surplus shop.
This unit has same fail.

cpuDiagDsyAccess ............... pass
dsp68kMemTest .................. ***FAIL***
..error details:
ERRORID: 162 diagnostic test failure dsp68kInMemTest
** addr = 0x7000000  exp data = 0x7fffff00  actual = 0x7f5fff00

Reason:  one of three bad  SRAM for   Tristar DSP
U870(middle below ), U871(middle upper, this is bad), U872 (upper). 

Greetings
Matt

BTW: dsp68kD1MemTest  = bad U1008 or U1009.

[snoopy]

I got a 784A that did a similar thing and everyone was saying that it was one of the memory chips but I located it to some dry solder joints on one of the big arse QFP chips on the main acquisition board. Use a fine dentist tool and carefully pull on each leg of the QFP and see if it is firmly soldered to its pad.