I got this TeleTone TV about 10 years ago (maybe longer) and when I got it - it was totally dead. After replacing a couple of burned out resistors in the power supply and heater string, there was sound but no picture to speak of. Nearly all of the filter capacitors are bad, so I replaced a few of them and tacked some temporary replacements in other places, the result was a fairly bad picture.
My only goal was to determine if there was any life left in the 7JP4 CRT - they are now almost impossible to come by, so I just tacked in what I had lying around parts-wise.
Satisfied that I had something to work on, I ordered some replacement parts, but soon after I moved and the TV got buried somewhere. It's been at least 7 years since it got turned on, so I powered it up through the iso-transformer and variac. I got intelligible sound at about 85VAC and a visible picture at about 100VAC. In some ways it was better than the picture I got before as there were no hum bars but it was nowhere near as sharp (sharp being a relative term)
It's very unstable, requiring almost constant adjustment of the hold controls and the picture is much too large.
This set is interesting in construction, the RF/IF/Video/HV and audio sections are on the bottom chassis while the deflection circuits and the CRT chassis is mounted on the side of the cabinet. In the upper left is the antenna, which essentially is 2 "tape measure" type reels.
This is the bottom of the sweep chassis, the largest of the brown "paper" capacitors are rated at 6000V and are likely bad, I have replacements now. The other problem is the high voltage dividers for the focus and deflection voltages. The design itself is inadequate, the resistors are not designed to withstand the voltages they are being subjected to and their lives will be very short. A proper repair would require the use of special high voltage resistors ($$)
My next step is to replace the high voltage capacitors in the deflection circuits and see what happens. My guess is that the high voltage is being dragged down, causing the picture to be larger and dimmer than it should be. We'll see how wrong I am.
My only goal was to determine if there was any life left in the 7JP4 CRT - they are now almost impossible to come by, so I just tacked in what I had lying around parts-wise.Satisfied that I had something to work on, I ordered some replacement parts, but soon after I moved and the TV got buried somewhere. It's been at least 7 years since it got turned on, so I powered it up through the iso-transformer and variac. I got intelligible sound at about 85VAC and a visible picture at about 100VAC. In some ways it was better than the picture I got before as there were no hum bars but it was nowhere near as sharp (sharp being a relative term)
It's very unstable, requiring almost constant adjustment of the hold controls and the picture is much too large.This set is interesting in construction, the RF/IF/Video/HV and audio sections are on the bottom chassis while the deflection circuits and the CRT chassis is mounted on the side of the cabinet. In the upper left is the antenna, which essentially is 2 "tape measure" type reels.
This is the bottom of the sweep chassis, the largest of the brown "paper" capacitors are rated at 6000V and are likely bad, I have replacements now. The other problem is the high voltage dividers for the focus and deflection voltages. The design itself is inadequate, the resistors are not designed to withstand the voltages they are being subjected to and their lives will be very short. A proper repair would require the use of special high voltage resistors ($$)
My next step is to replace the high voltage capacitors in the deflection circuits and see what happens. My guess is that the high voltage is being dragged down, causing the picture to be larger and dimmer than it should be. We'll see how wrong I am.
1 comment:
reminds me my grandad fiddling with gadgets in the shed, interesting read!
newman
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