TDS644A not working - Page 1
Forum section: electronics / repair

author: Daxxin
author_rank: Regular Contributor
timestamp: December 15, 2015, 02:28:26 pm
content: Hi , got this scope from ebay for parts , replaced all smd electrolytics caps almost all errors gone excepr one regarding tp heatbut when i replaced nvram chip DS1650Y , getting more trouble ..cant read the old chip by programmer seems destroyed whileremoving it then i download an backup and installed the new chip then booting but now i get eror message while try to checkthe errors log ..when pressing menu before to arrive to Error Log menu it hangs on CAL never reach Diag/ErrSHIFT+UTILITY -> CONFIG -> IO -> CAL -> Diag/Errand show this:this the start up log banner:then i found this opamp running very hot the measurement is different from schematiccompunents surrounding is fine no shorts .if someone has working nvram pls upload . Thanks

author: nctnico
author_rank: Super Contributor
timestamp: December 15, 2015, 05:25:24 pm
content: Try the attached file... I pulled it from a working TDS644A

author: Daxxin
author_rank: Regular Contributor
timestamp: December 15, 2015, 05:54:33 pm
content: Tanks Ntnico now i get only acquisition board fault and i can read error logany idea whats wrong?

author: nctnico
author_rank: Super Contributor
timestamp: December 15, 2015, 07:34:20 pm
content: 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.

author: feedback.loop
author_rank: Frequent Contributor
timestamp: December 16, 2015, 07:19:14 am
content: Where did you get the schematic?

author: nctnico
author_rank: Super Contributor
timestamp: December 16, 2015, 07:25:09 am
content: 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.

author: Daxxin
author_rank: Regular Contributor
timestamp: December 16, 2015, 10:18:43 am
content: Thats right Ntnico not worth much this scope lacking some important functions anyway thanks for your big helpi try to fix chenking traces , schematic is available over internet just google easy to find it , but is incomplete pdf lacking some initial pages.

author: Jwalling
author_rank: Unknown
timestamp: December 16, 2015, 11:32:32 am
content: Quote from: feedback.loop on December 16, 2015, 07:19:14 amHere you go!http://hakanh.com/dl/kits.htmGood luck.Jay

author: nctnico
author_rank: Super Contributor
timestamp: December 16, 2015, 03:06:22 pm
content: There is also the TDS520B component level service manual with full schematics. The Tektronix TDS500/600/700 series oscilloscopes don't differ that much.

author: Jwalling
author_rank: Unknown
timestamp: December 16, 2015, 08:16:01 pm
content: Quote from: nctnico on December 16, 2015, 03:06:22 pm*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

author: Jwalling
author_rank: Unknown
timestamp: December 16, 2015, 08:20:48 pm
content: Quote from: Daxxin on December 16, 2015, 10:18:43 amIs 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

author: nctnico
author_rank: Super Contributor
timestamp: December 16, 2015, 10:43:56 pm
content: Quote from: Jwalling on December 16, 2015, 08:16:01 pmIf 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.