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Vintage Television and Video Vintage television and video equipment, programmes, VCRs etc. |
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19th Oct 2021, 7:21 pm | #1 |
Hexode
Join Date: Jan 2007
Location: Beckenham, London, UK.
Posts: 373
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Sony 8-301W
This set claims the title of the first direct view transistor portable in the world (though some would dispute that). It appeared in 1960/61 and was mainly for the American 525 line market though a European version was produced in limited numbers.
The one I picked up turns out to have an o/c tube heater (sob sob). Apart from that it has an interesting line fault. The line Output stage is drawing 1.6 amps when it should be doing about half of that. I thought it might be faulty scan coils but disconnecting them only brings the current down to about 1.4 amps. In fact all the voltages out from the LOPT are about right and disconnecting every line from the LOPT did not reduce the current significantly. This got me scoping the waveforms. The waveform at the base of the horizontal driver transistor is about correct, but what appears at the collector is weird as per the attached photo. You can see that the flyback period is about twice as long as it should be at 20mS and has a weird kind of double triggering pulse. (the scope is set to 10mS/div). This is definitely not how it should be according to the manual! I have checked/changed everything around the driver circuit barr the transistor itself. Does anyone have any thoughts? |