Author Topic: repair help needed on tek tds 680b, same psu as 520b  (Read 1333 times)

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Offline Arjan Emm

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repair help needed on tek tds 680b, same psu as 520b
« on: May 09, 2015, 03:57:52 pm »
I bought a cheap 150 euro tektroniks tds 680b not long ago. I bought it in not working condition but it turned out to be in calibration mode. I flipped the switch inside and it worked. All self tests checked positive.
After a week on standby i woke up in the morning and found that the gfi of my house installation tripped, 20 mA, no fuses just the gfi. Flipped it back on and no problems, everything in the house worked except the tek, appears to be completely dead.
I measured the voltages on J27/6 and J26/5, nothing at all.
The main cap on A17 charges too 325V as it should. The scoop draws about 100 mA when turned on by the main switch. The standby on off switch doesn't do a thing. the push button on the A11 mainboard and shorting pin 3&5 on jumper J26/5 also don't start up the psu. 0V on all output voltages.
I followed the trouble shouting table in the TDS 520B, 540B, 620B, TDS 644B, TDS 680B,
TDS 684B, TDS 724A, TDS 744A, & TDS 784A service manual. and it comes down to replacing the psu.
And i looked at the TDS 520B Mod CM Digitizing Oscilloscope Component Service Manual. It has a complete schematic of the psu.
I in circuit measured the main switchers and they the appear allright, hence the fuse stays in.
But i'm at a loss now. No popped parts, just dead. Any ideas anyone?
« Last Edit: May 09, 2015, 04:01:53 pm by Arjan Emm »
 

Offline SaabFAN

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Re: repair help needed on tek tds 680b, same psu as 520b
« Reply #1 on: May 09, 2015, 06:24:16 pm »
I just read an article on a website where someone described how he revived a TDS 524A. He spoke about a Transistor that is responsible for the standby-power that blew up.

Link to his website: http://jvgavila.com/tds524a.htm
Maybe that's a start?

Offline Arjan Emm

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Re: repair help needed on tek tds 680b, same psu as 520b
« Reply #2 on: May 09, 2015, 07:22:16 pm »
Thanks, i saw that link before. It seems a slightly different supply. My psu does have a tap on the cooling element for that falty bu508. But no option on the pcb to install it.
 


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