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Vintage Television and Video Vintage television and video equipment, programmes, VCRs etc. |
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29th Jul 2021, 3:48 pm | #21 |
Octode
Join Date: Apr 2005
Location: Peterborough, Cambridgeshire, UK.
Posts: 1,898
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Re: Perdio Portarama 3 and a bit?
It does sound like a prototype if it is it is lucky to survive as often prototypes were destroyed or broken up for parts once production had started (or not).
I scrounged loads of panels that had been made as prototypes by a local industrial electronics firm there were many signs of modification like cut print linked by a resistor capacitors tacked on the back etc. Your set may be the only surviving one! An interesting set. I am following with great interest! Rich |
30th Jul 2021, 4:21 pm | #22 | |
Heptode
Join Date: Apr 2003
Location: Cornwall, UK.
Posts: 989
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Re: Perdio Portarama 3 and a bit?
Quote:
.........That’s a valid point, RtoB! However, I was pretty confident that I could resolve the frame issue easily by changing 2 components. This part of the frame stage is very similar to that in the Portarama MK2, and I’ve fixed a couple of these in the past. The fault was due to two ‘reversible’ electrolytic capacitors which were acting more like resistors. As it was easy to re stuff, this was carried out and now I had full height. The line speed didn’t seem too far off, but it was way out of range of the line hold control. Due to the fragility of the pcb print, I really didn’t want to start lifting components to check them without good reason. Unfortunately, the only circuit I have for the MK3 is a Trader sheet (1853/T345) which does not give any transistor voltage readings, in fact I can only see two voltage references on the whole sheet! I carefully adjusted the core of L14, (the line oscillator coil)to bring oscillator within adjustable limits, and then it was plain to see that whilst I had a locked frame, the line would not lock at all. C62 (1.25uF) in the flywheel sync circuit was responsible here, and when replaced, the line oscillator coil could be adjusted back into its former position. So, a bit more progress.....but more to do. The AGC does not appear to be operating correctly, and the set is a bit temperamental if it’s moved, leading to either signal loss or complete frame collapse. The off screen pictures below show a Test Card on 405, and an off air programme on 625. The set is drawing an average of 1.25Amps at 12 Volts from my bench power supply, so it’s not too power hungry! Cheers. SimonT.
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The honesty of imperfection.......... |
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