Sinclair mtv1

[jr_tech]

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?

[timmy]

Originally Posted by jr_tech

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?

Yes I found them in the right tuner thanks and the mpn3404 I looked up and it's app is for the vhf tuning. I have a dead raster bright on but no snow which does indicate the tuner is waiting for an antenna. The sound is snow but no real sound. I'm just not sure why I would get a momentary reading in the opposite direction and if these diodes are said to be checked like any other diode then maybe they are leaking or maybe normal so until I get the rest out maybe I will find one open. Otherwise there is nothing on the battery board that I found wrong. I wish it were that easy to find a simple problem.

[jr_tech]

"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

[timmy]

Originally Posted by jr_tech

"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

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.