Motorola ts907 low hv - Page 46 - Videokarma.org TV - Video

timmy · #1 10-17-2022, 03:19 PM

Quote:

Originally Posted by Yamamaya42

it be best not to disturb them yet, I would try fresh power resistors first.

if they are messed with, it will shift the alignment.

I would think it’s not likely that both would go bad at the same time. These resistors are heavy wire wound I have never seen one of these rise in tolerance.

Yamamaya42 · #2 10-17-2022, 03:28 PM

3w resistors are rather cheap now, and much smaller and run cooler than in the 60s, replacing them all won't cost much more than $10, and make SURE 100% that it's not a resistor problem, which is a good thing to do before looking at caps IMOH.

timmy · #3 10-17-2022, 03:46 PM

Same as the 2 .001 caps what’s the likelihood of both of those caps being bad. They are ceramics and I’m surprised that it wouldn’t be mica caps in such a circuit.

Electronic M · #4 10-17-2022, 04:38 PM

Ceramics almost never fail and when they do it's usually in sweep circuits where they're being whacked with several KV worth of pulses, not <300VDC and <3VAC that the IF subjects them to...

If you are concerned about the ceramic caps in the IF leaking current I gave you great advice before... Temporarily stick a cap 100X the capacitance in series. It will stop DC leakage and the series capacitance will be almost exactly the same as the original part alone.

old_coot88 · #5 10-17-2022, 06:27 PM

The bulletproof-ness of ceramic caps is a fact. The only defective one I ever encountered was inside the motor of a cassette player. The complaint was sporadic overspeed. The motor had a 3-segment commutator, with 3 tiny ceramic caps bridging the gaps between segments. One of the caps was leaky, and replacing it cured the speed problem.

Yamamaya42 · #6 10-18-2022, 07:50 AM

Since you stated that the voltages on pins 7-8 of the V1-V2 are wrong, but the 6EH7s are NOS, and the problem is not a bias 275v problem and extremely unlikely to be disc cap related, then once again the best path is to replace the power resistors, no matter how they seem to check out.

List here.
main power diodes
https://www.mouser.com/ProductDetail...2B4kkscA%3D%3D

6.8k 3w (r40, r49)
https://www.mouser.com/ProductDetail...0BKWoLFQ%3D%3D

2.7k 3w (r41, r50)
https://www.mouser.com/ProductDetail...Wwtn4Z2Q%3D%3D

8.2k 3w (r39 , r48 )
https://www.mouser.com/ProductDetail...2a7TUHog%3D%3D

Yes, use all 3w resistors, they will be smaller then the ones replaced, and much more reliable.
In fact replacing all resistors in the IF may be the only way to get it working again, and even then, you may not be able to.

timmy · #7 10-18-2022, 12:35 PM

When using the ohms chart for tube sockets use with tube in or out.

Yamamaya42 · #8 10-18-2022, 12:40 PM

Quote:

Originally Posted by timmy

When using the ohms chart for tube sockets use with tube in or out.

tubes in, but it does not really matter much, since only the heaters will alter the readings you may be taking, which will be low anyway, so if you do it tubes in via a test socket under the tube, or out, just probing socket alone, you should get same readings.

timmy · #9 10-18-2022, 12:52 PM

I’m getting a really bad reading on pin 8 of v1 should be 3200ohms 3.2k I’m getting 6.30k I figured I would check resistance on v1 and v2

Yamamaya42 · #10 10-18-2022, 01:07 PM

Quote:

Originally Posted by timmy

I’m getting a really bad reading on pin 8 of v1 should be 3200ohms 3.2k I’m getting 6.30k I figured I would check resistance on v1 and v2

You are aware of the note “measured from the output of X2” that would be the cathode of the diode, before L54, and not ground, if this is what you are doing, then it's a good sign the power resistors are bad, but if you are measuring from ground, your readings are wrong.