TDS644A not working

[Daxxin]

Hi , got this scope from ebay for parts , replaced all smd electrolytics caps almost all errors gone excepr one regarding tp heat
but when i replaced nvram chip DS1650Y , getting more trouble ..cant read the old chip by programmer seems destroyed while
removing it then i download an backup and installed the new chip then booting but now i get eror message while try to check
the errors log ..when pressing menu before to arrive to Error Log menu it hangs on CAL never reach Diag/Err
SHIFT+UTILITY -> CONFIG -> IO -> CAL -> Diag/Err 
and show this:


this the start up log banner:


then i found this opamp running very hot the measurement is different from schematic
compunents surrounding is fine no shorts .


if someone has working nvram pls upload . Thanks

[nctnico]

Try the attached file... I pulled it from a working TDS644A

[Daxxin]

Tanks Ntnico now i get only acquisition board fault and i can read error log



any idea whats wrong?

[nctnico]

Did you also replace the capacitors on the front panel? You may want to clean the boards as well to get rid of all the electrolyte. BTW I'm not sure whether the TDS644A is worth it because it has a short memory and no peak detect.

[feedback.loop]

Where did you get the schematic?

[nctnico]

Regarding the opamp: I'd desoldering it using hot air and inspect all traces underneath it. Chances are it gets no power or the electrolyte did other damage.

[Daxxin]

Thats right Ntnico not worth much this scope lacking some important functions anyway thanks for your big help
i try to fix chenking traces , schematic is available over internet just google easy to find it , but is incomplete pdf lacking some initial  pages.

[Jwalling]

Where did you get the schematic?

Here you go!
http://hakanh.com/dl/kits.htm
Good luck.

Jay

[nctnico]

There is also the TDS520B component level service manual with full schematics. The Tektronix TDS500/600/700 series oscilloscopes don't differ that much.

[Jwalling]

There is also the TDS520B component level service manual with full schematics. The Tektronix TDS500/600/700 series oscilloscopes don't differ that much.

*sigh*
Incorrect. The TDS620 and 640 series ACQ boards are completely different from TDS500X and TDS700X. Please be sure of what you are saying before making blanket statements like these.

Jay

[Jwalling]

Thats right Ntnico not worth much this scope lacking some important functions anyway thanks for your big help
i try to fix chenking traces , schematic is available over internet just google easy to find it , but is incomplete pdf lacking some initial  pages.

Is the schematic in the link I posted incomplete? (Not sure as I never looked at it too closely - I stopped working on them years ago because of the capacitor mess!) 

Wouldn't touch them now with a 39.5 foot pole. 

Jay

[nctnico]

There is also the TDS520B component level service manual with full schematics. The Tektronix TDS500/600/700 series oscilloscopes don't differ that much.

*sigh*
Incorrect. The TDS620 and 640 series ACQ boards are completely different from TDS500X and TDS700X. Please be sure of what you are saying before making blanket statements like these.

If you repair stuff without exact schematics then you have to be creative in your mind and do with what you have. Most of the damage in these scopes is done by leaking electrolyte into to opamp circuitry which mostly provides various reference voltages. This is a concept which is shared between these scopes. Know that and you can recognise the circuits and trace the problem back to it's origin.