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Vintage Test Gear and Workshop Equipment For discussions about vintage test gear and workshop equipment such as coil winders. |
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7th Aug 2020, 10:07 am | #1 |
Pentode
Join Date: Oct 2018
Location: Carrickfergus, County Antrim, Northern Ireland, UK.
Posts: 126
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Marconi 2955
Hello from Dave, I am seeking advice from those more knowalgeable than me. I have a 2955a from a friend which I have found out that the LOPT has gone short circuit to ground. I was measuring for voltage on the collector of tr3 the line output transistor and found no volts,however there was volts on wire 2 and wire 10 which suggests that a track internal to the board has blown. I advised my friend that his LOPT has died and he thought about taking the video signal from inside and bringing it out to an external monitor. On looking at the circuitry arround the LOPT there is a 24 voly supply generated to feed the keyboard so there would have to be a 24 supply supplied to replace the one generated from the LOPT. Also the frame sync and line sync would need to be brought out. What I would ask of you,is this feasible or a waste of time? Another thought is that possibly when the LOPT failed would further damage have been caused to the keyboard circuitry.
This is the first time I have attempted to repair one of these instruments. Dave |