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Yes, I am using the on-line schematic... somewhat hard to read, but the 2 tuner schematics (pages 15 & 16) are pretty clear. I expand the picture as necessary on this iPad. The varicap diodes are fairly easy to locate, just follow the lines from the "tuning" input(s) of each tuner down to the 33k isolation resistors to the VC diodes.
I have no idea how to check them or how to find replacements. jr |
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Last edited by timmy; 11-07-2017 at 06:38 PM. |
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The tall slender tuner standing up on the board is connected to the UHF antenna, the fatter shorter tuner under the copper shielding is connected to the VHF monopole antenna, so I think that pretty much shows which is which.
Sure you can test for diode action, but a more complete test would necessarily involve some method of applying voltage to the varicap diode and measuring its change in capacitance as you change the voltage. I still think that you have a more basic problem than tuning, since you have no raster. jr edit add: I believe the MPN 3404 is a switching diode, not a varactor... are you sure you found the correct part? Last edited by jr_tech; 11-07-2017 at 07:20 PM. Reason: add 3404 question |
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"the mpn3404 I looked up and it's app is for the vhf tuning"
I don't think so, I believe the 4 MPN3404s that you located are used for band switching. They are VHF switching diodes, not varactor tuning diodes. jr |
Audiokarma |
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Well yes they are and the others in there are 3 leg transistors there is nothing else. These varicaps were explained in the thread I read from England so I hope I find a bad one . I seen listings calling then varicaps as well as varactors also.
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