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HP 1741A oscilloscope - restoration project

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atlacamani:

--- Quote from: peterpan on March 26, 2019, 09:34:21 am ---Listen to my friend!
HP makes your job easier: there is a number for each wire connection, eg. 956. Equal to the color of the matching wire according to the resistance color scale: 9white, 5green, 6blue equal to white wire with blue and green stripe. I tak dalee ...
Hi. PP

--- End quote ---
thank you friend))

jeno:
Hi, I just got a HP 1741a oscilloscope, and the power supply is bad, none of the voltages match their rating, i replaced two burnt resistors, one of the power tranzistors and some capacitors and still nothing, anyone help?

lowimpedance:
What voltage is coming out of the bridge rectifiers ?, they do have a hard life so check for dry joints etc .
Also the transistor connectors for the pass transistors on the rear panel maybe not making good contact.
Just tossing a few ideas, perhaps a few good pictures of your power supply PCB if you think it useful unless its pristine :).
One other point to note is odd symptoms can also be caused by resistors that have drifted high upsetting critical bias points in the DC coupled circuits, both power and signal paths.

jeno:
After replacing the bridge rectifier for the +15v rail bridge rectifier, all of the filter caps after the bridges, I have all good voltages at the diode bridges, +5v, +15v, -100v rails are fine but the +48v is reading 26volt and the +120v is at 188v, at the +48 and the +120v the 2w resistors were totally burned i replaced them but still not ok, for the -15v my regulator ic is bad, ill try to put an LM723 for that. But I noticed that the horizontal output board is also has some burnt parts, but I dont have the schematic for that, even for the power supply I paused Dave's video when he showing the schematic.

jeno:
I also need to get somehow the values of theese components, or the horizontal output schematic

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