Electronics > Repair

Tektronix 7904 Repair

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Z-axis is blanking. I checked that on TP1883. I'm not 100% sure HV is there, but the anode wire clicks with HV static and is attracted to my finger.

Update: What the fuck is wrong with this scope? It works perfectly now?!!!! I didn't even change anything! CRT was dead before, but then after a while, it suddenly came back? I have no clue. I was just probing around when I looked at the 7904's display I saw a TRACE. Maybe bad solder joints? Thermal issue?? Bad capacitor???? NO IDEA.

Maybe my scope is haunted. I still do not know what component failed and created smoke. I saw a lot of smoke come out of the instrument. But I can't find what failed. I guess I'll just follow "If it ain't broke, don't fix it" saying unless someone proposes an idea.

I recently repaired some 7804 plugins after the smoke escaped, it was the low value series resistors in the power feeds to the tantalum decoupled supplies to the plugin circuits which had burnt. the burnt resistors became open circuit and where difficult to spot. The rest of the scope continued to function when the resistors were fried. The cure was to replace both resistors and capacitors. hth David.

The 7904 has two lamps in the A trigger source selector board/switch burnt out.

Replacing the lamps are pretty straight forward, my issue is that I don't know how to remove the trigger selector board. I RTFMed, but it doesn't mention anything for removing it.

Any help would be appreciated

Photo: https://groups.io/g/TekScopes/album?id=293799

Update: Figured it out:  https://youtu.be/1XTmbKJs9PY


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