Electronics > Repair

Tektronix TDS2024 Oscilloscope - Repair Log

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tautech:

--- Quote from: sean0118 on August 15, 2021, 05:15:56 am ---Okay the display is actually working, it's just really, really hard to see without the backlight.

I saw other people have upgraded their TDS scopes with LED strips, I might need to do something similar, unless I can fix the backlight power supply.

--- End quote ---
Good progress !  :-+

Do you have another scope to help diagnose the backlight supply ?
Looking at my PSU it just looks like a push/pull oscillator and you should be able to sense the EMI with another scope probe held near to see if it's oscillating.
Some years back I was given a TDS1002 with a dead backlight and it just turned out to be the C in the RC for the oscillator had drifted into the pF and it wouldn't oscillate anymore. Replacing the C fixed it. 

sean0118:

--- Quote from: tautech on August 15, 2021, 05:26:17 am ---Do you have another scope to help diagnose the backlight supply ?
Looking at my PSU it just looks like a push/pull oscillator and you should be able to sense the EMI with another scope probe held near to see if it's oscillating.
Some years back I was given a TDS1002 with a dead backlight and it just turned out to be the C in the RC for the oscillator had drifted into the pF and it wouldn't oscillate anymore. Replacing the C fixed it.

--- End quote ---

Thanks, that's a good idea.

A bit of smoke did escape from that area of the board when the power rails doubled in voltage (backlight was lighting up before that). I did pull and test the cap and two transistors earlier, but I should double check.

If all else fails I might do some transformer surgery.

tautech:
Yeah well I'd certainly be checking the primary, secondary and local resistors.
Sing out if you need the xformer winding resistances.....secondary easy to measure = 430 ohms.  :)

sean0118:
Transistors and capacitors seem okay (just testing with a multimeter). Resistors are a good point, I still need to test them.

On the transformer I'm getting 177 Ohms for the colour display winding and 2M for the black and white. If you're getting 430 I assume I have a problem.


edit: Looks like there's two winding on the primary with a center tap? I'm getting ~1k for each.

sean0118:
Okay I pulled the transformer.

The primary windings are not 1k, I was measuring a resistor.

I'm a bit confused about the circuit of the primary winding/s, but I'm getting ~0 Ohms between the three center pins, and ~0 Ohms between the two outer pins. I'm measuring open between the outer and inner pins. I hope that's not too confusing...   

Secondary windings are unchanged out of circuit.

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