Ts18 chassis Motorola

[Electronic M]

Have you checked tube bias voltages against the schematic, swapped RF/IF tubes cleaned sockets, checked for open coils etc.?

[Polaraligned]

I would never, ever turn the IF transformers, unless you know that somebody had previously turned them. And then, you had best be prepared for a full sweep alignment. This set sounds like it needs a careful and systematic troubleshooting.

[timmy]

Did swap tubes and I do think someone played with the transformers as there is shiny spots that show where the screws were. I use a digital vom in diode test to see if there were any opens in the coils and checked the connections of the coils and they are in place.

[timmy]

Well I think what's next is checking resistors in the If section because I'm sure if one resistor in the right place along the IF is bad I'll get the same result. I do have sound on channel 3 so it's not that far off and when I say turning the IF trans I meant half turn then right back I do know better then to turn them at random and then a full alignment will be needed and I don't want that to be the case since I don't have the means to do that correctly .

[Kevin Kuehn]

You know, for a reasonably small investment, you could have yourself a B&K 1077 Analyst. Those things come in really handy when you get into these "I don't know where I've lost my signal" situations.

[Electronic M]

One thing that comes to mind: you put a new diode in parallel with the original detector (which confirms it ain't open), but did you test the resistance of the old diode both directions to confirm it is not shorted?

If it's shorted it could explain both symptoms you have.

Tuning RF/IF coils should always wait until it's last resort time, and all components have been tested.

[old_coot88]

Originally Posted by Electronic M

Tuning RF/IF coils should always wait until it's last resort time, and all components have been tested.

And even then, turning of the video IFs should never happen unless one is equipped with a sweep genny and 'scope and knows how to do alignment, AND there's clear-cut evidence of misalignment (ringing and/or smearing of fine detail in the pic), and subbing the IF tubes doesn't fix it.

[Electronic M]

Originally Posted by old_coot88

And even then, turning of the video IFs should never happen unless one is equipped with a sweep genny and 'scope and knows how to do alignment, AND there's clear-cut evidence of misalignment (ringing and/or smearing of fine detail in the pic), and subbing the IF tubes doesn't fix it.

Agreed. Though some service prints give data for a sweep-less peaking alignment using a simple sine-wave generator, some adjustments like traps are meant to be peaked to a frequency and can be set the same way.

I remember one guy here who properly aligned a Dumont by eye....I would not try or recomend that, but MAN was it ever impressive....

[timmy]

I clipped one leg of the diode and checked it for shorts and got no beep either way on that 1n34. Would I even get an ohms reading from that diode? I did check voltages on the 12at7 and pin 1 128 Vic and says it should be 107 Vic , pin 4 41 vac, 38 vac pin 5 41 vac, I get no ac except 236 Vdc , and pin 6 is to be 215 Vdc, I get- 1.0 Vdc . V6 a 6au6 pin 5 215 Vdc I get 87 Vdc and pin 6 232 Vdc I get 171 Vdc. It's wacky... Well I check the 1n34 for any ohms and got nothing either side with one leg off and also check the spare I got and that one had no ohms either.

[timmy]

I wonder if this is something to do with the contrast control being as it acts like a tuner to much one way and sound and pic is gone. The pot measures good but there are several caps on this pot...

[Polaraligned]

You need a meter that has a diode check setting. It won't conduct unless it is forward biased, and then it will conduct in one direction only if it is good.

[timmy]

I do have a digital diode check and get nothing either side of it including ohms nothing either side of the diode.

[Polaraligned]

Sounds dead to me. PM me your address again and I can drop a good one in the mail for you.

[timmy]

are these 1n34 diodes supposed to give a reading in ohms or diode check because i have another one from another set and get nothing from that one either unless that second one i got is bad as well. i know some diodes wont get readings so i dont know about these. the replacements are nte109 IIRC ?

[Polaraligned]

I don't know what meter you are using, but my Fluke gives me the voltage drop of the diode. For example, a germanium diode will read approx 0.3v when forward biased and OL (over limit) when reverse biased. If you use an analog VOM, it will give a resistance reading when forward biased and read infinity when reverse biased.