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Vintage Television and Video Vintage television and video equipment, programmes, VCRs etc.

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Old 2nd Feb 2024, 12:20 pm   #1
regentone001
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Default RGD 612 tuner (Regentone 17-18)

Having had no joy with a request for a replacement I decided to have a go at repairing the one in the set.
It had decided to emit some smoke and the 30C15 valve had displayed some nice blue flashes. On dismantling the tuner I found that 3 resistors r11 33k now read 47k, r12 100k was now open circuit, and r10 10k was reading roughly half of what it was meant to be. I replaced the 3 of them reassembled the tuner and tried it out. Still no joy but no burning and no blue flashes, a different 30C15 had also been installed. It is basically impossible to take voltage readings in the tuner but the HT feed via r15 6.8k on the main circuit board is reading 210 volts which is roughly the same as the main HT rail. When I press one of the channel change buttons I do get a bit of noise on the screen and also via the sound channel. It never worked correctly, it had been fiddled with, and only used to work on channel 1, channel 2 would give a very broken up picture but only vision on sound on the sound channel and that was about all I could get out of it.
Any help would be appreciated
Steve
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Old 2nd Feb 2024, 1:59 pm   #2
ronbryan
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Default Re: RGD 612 tuner (Regentone 17-18)

If you feel that the tuner is taking little current, have you checked the 120 ohm cathode resistor of the cascode RF amplifier? You can do this with the set off, valve removed, and connecting between the appropriate valve base pin and ground with your meter.

Measuring valve voltages in tuners can be achieved by stripping both ends of about 1.5" of solid core wire and wrapping one end one turn around the valve pin under investigation, bringing the wire up past the valve body. Replace the valve carefully and bring the wire up past the valve base screen, omitting any removeable screening can. I have found wire-wrap wire works well as it is slim (usually 30awg) and silver plated. This is a useful fault finding technique for checking for negative volts on the oscillator grid, to prove that it is running, for instance.

Ron
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Old 3rd Feb 2024, 3:47 pm   #3
regentone001
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Default Re: RGD 612 tuner (Regentone 17-18)

Thanks for the idea for reading the voltages Ron but the tuner has fixed screening cans and is all but impossible to access, even changing the valves can be a challenge as they are right under the "bowl" of the crt and have to be accessed across the full depth of the main circuit board as can be seen in the picture of the above chassis view. P.s having taken that picture I notice they have the wrong tube number as it is an AW43 88 not MW 43 88 that is from the Regentone service manual too
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