Tek TDS320 repair help -SOLVED!

[halexa]

Hi,

Got a TDS320 with no working buttons or roatary switches on the front panel, except those around the screen.

I have removed the front panel PCB and replaced two leaking caps C132 and C131. But that did not solve the problem.
C132 has 5V across itself and its supplying the MCU.
C131 on the other hand has 0V across and after tracing were it went it's supplying the MCU-VRH pin which is ADC voltage reference high. I guess there shall be a voltage present there.

Do any of you have the schematic for TDS320? It would help my trouble shooting alot and to find the source of the MCU ADC reference voltage.

I have tried the Tektronix service manual troubble shooting procedure but it only tells me to replace the front panel PCB.

[rustybronco]

Will this possibly help? http://w140.com/tektronix-tds380-tech-ref-schematics.pdf

[xwarp]

You are going to have to look closer at the traces on the front panel control board and make sure that there are no traces that have been eaten away.

I had an open trace on the TDS460 that I have because of the leaking cap that was replaced.

[halexa]

@rustybronco  Thx fro the schematic, its not the same circuit but the MCU is the same and theory of operation. So it can get me some clues, I will study it a bit more tonight.

@xwarp Yepp will do that. The trace for the VRH pin is OK to the connector to the main board. I need to check were it's going on the main board.

I checked all ribbon cables and the PSU voltages and they are all OK.

[xwarp]

You might want to check and see if there is a common line running to the buttons for a signal.

Also, be careful about cleaning those traces, I believe even alcohol will rub them off.

[halexa]

You might want to check and see if there is a common line running to the buttons for a signal.

Also, be careful about cleaning those traces, I believe even alcohol will rub them off.

Yes already made that mistake The button traces on the flat-flex around the screen was not very rigid. But i manage to fix the one i messed up with conductive paint.

[xwarp]

Yep, I had to do the same with multiple traces on mine. Tedious job it was.

[Dtec]

Take a ic led flashlight and in the dark you will see the leakage from the caps and what traces they have affected


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[halexa]

Hi,

Think I found the issue.
A track was eaten up under the main connector. The track was connecting RST pin of MCU to the main board. No wonder noting worked.

[Armadillo]

That is a Great Microscopic discovery. ! 

[halexa]

Hi

Put everything together again and it works like a charm, every button and knob is fully functional.  .

[alm]

Congrats on the repair!

[james_s]

Nice job, I repaired a similar problem on one of these but it was a short between two traces. I like the TDS300 series scopes, they're simple and easy to work on, fairly reliable and they perform quite well for a scope that can be had for ~$100.