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#1
11-01-2016, 10:43 PM
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Recapped power supply in Blonder Tongue AM60-550B and no more picture
I just picked up a Blonder Tongue and after my initial setup noticed the 60 Hz bars in my picture. So before I get this set up in its final place I figured I would replace the electrolytics on the power supply board. After reassembling everything, I now have sound but no picture, and the modulation lights are lit up even with the dials bottomed out. I get a nasty audio buzz on the TV when I turn the AGC control off on the back of the unit, and the status light has a fast flash. I have been trying to use channel 7, but the problem is consistent between channels. What did I screw up?
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#2
11-02-2016, 08:26 AM
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Did you observe polarity when changing the caps? Did you use good quality new replacement caps?
__________________
Tom C. Zenith: The quality stays in EVEN after the name falls off! What I want. --> http://www.videokarma.org/showpost.p...62&postcount=4
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#5
11-02-2016, 11:27 AM
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Another thought is that if one of the caps NOT in the power supply that is still original has shorted/become leaky it could be sagging PS voltages globally or locally (if there is a resistor between it and the PS rail) which could cause hum and similar symptoms.
I often look at all the lytics in the unit with an ESR/leakage tester when changing caps.
__________________
Tom C. Zenith: The quality stays in EVEN after the name falls off! What I want. --> http://www.videokarma.org/showpost.p...62&postcount=4
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#6
11-02-2016, 02:08 PM
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https://goo.gl/photos/4jtJQiQGPmxqE7xs5
Other than the smaller caps on the power supply board, the only other large value electrolytics are on the AGC board. I suspect one or a few of these may be bad. I don't think anything is connected erroneously on the power supply board as there was only 2 connecters, and one wire lead.
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#7
11-02-2016, 02:18 PM
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Are the power rails coming up properly? Measure the voltages at the 3 test points on the power supply board. If not, try rechecking with the output connectors (the single wire and the small 4 pin one with the grey wires) disconnected, to see if the issue is in the power supply, or an excessive load somewhere else in the circuit.
Did you replace the SMD electrolytics, as well? They can fail just like the larger through-hole ones do.... Last edited by N2IXK; 11-02-2016 at 02:23 PM.
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#9
11-02-2016, 03:07 PM
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Quote:
Size/value of the lytic don't matter. If it becomes electrically leaky or shorted it can cause problems...Yeah the big ones are the first you want to do, but if that fails the smalls also deserve consideration....If you changed the filters on a tube radio or TV and that did not completely fix it, you would change the papers next, right?...Same thing here.
__________________
Tom C. Zenith: The quality stays in EVEN after the name falls off! What I want. --> http://www.videokarma.org/showpost.p...62&postcount=4
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#11
11-03-2016, 10:57 AM
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The video and RF connectors on these things tend to be flaky.
Try DeOxit and wiggling. I got so fed up with two that I replaced the F connectors with BNCs.
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#12
11-07-2016, 08:24 AM
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I was hoping it would be something as simple as cleaning the video and RF connecters, but it made no change. The voltages I read off the power supply board seemed to be okay. Not sure what else to try at this point other than to replace the remaining electrolytics.
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