Motorola ts907 low hv

[Yamamaya42]

Originally Posted by timmy

No I’m not measuring from ground I’m on the second diode which would be x2 output

Then, that seems to point right at the power resistor networks I pointed this morning, replace all the 2-3 watts in the area, and the power diodes, cost from mouser, 10-15$

[timmy]

I’ll post the other resistance readings from v2 v3 because they are way off

[Yamamaya42]

As it has been mentioned before, by myself and others, your best hope to get this working is not to touch any capacitors in the area what so ever, and VERY CAREFULLY replace all resistors with 2% or better carbon film types, paying close attention to placement and lead dress, IE, try to make it look as close to the original as you can, and since technology has changed so much over the years and they have gotten smaller, it never hurts to go up one size in power rating, cause even if you do, what you are putting in will be physically smaller than what you take out, they are that much more efficient than the old ones.

[timmy]

Ok v2 and v3 are within good range only v1 is a problem
The only pin that’s not right is pin 8 should be be 3.2 but it’s measuring 6.30

[Yamamaya42]

R39,R40,R41 obviously, get all 3 in 3w, but I would not stop there, you should have R48,R49,R50 on hand as well in case. It would not hurt to change R22 as well.

[timmy]

R22 is a trap

[Yamamaya42]

Originally Posted by timmy

R22 is a trap

my error, that's R38, I jotted down the "22" next to the right number! :P

[timmy]

I will tell you I have the chassis out on the bench but this circuit should do what it has to on the bench and I put an antenna input and the voltage goes up very little so it’s resistor time I doubt it would have made any difference it it were in the set at this point

[timmy]

Ordered the resistors but I’m wondering where the 7 volts is coming from on v1 pin 2 it’s almost like the tube is locked on there for pulling the voltage down on pin 8 where on this tube is there something that would make it conduct or turn on full or partial.

[timmy]

I’m having a hard time believing those power resistors are bad because if they cannot supply the 100 v to pin 8 but only 60 v then I would think they wouldn’t be hot like they are working hard that’s why maybe the tube is partially on maybe not full but like an idle.

[Yamamaya42]

Originally Posted by timmy

I’m having a hard time believing those power resistors are bad because if they cannot supply the 100 v to pin 8 but only 60 v then I would think they wouldn’t be hot like they are working hard that’s why maybe the tube is partially on maybe not full but like an idle.

R 39,40,41 form a voltage divider, your resistance check of pin 8 found a problem with it, so replacing all 3 is the next logical step.

[timmy]

If I pull v1 the voltage go way up on v2 pin 8 but v1 pin 8 voltage stays the same low.

[timmy]

I don’t understand why the ohms go up slowly from 5k to 6.30k why slow it’s like it’s filling a cap. There is the one resistor that goes to ground and I hope something is not grounding that is not supposed to be. And I have new 1n4007 diodes I had put in and made no difference.

[timmy]

On the Motorola it has 2 rectifier diodes is 1n4007 ok for this or is there supposed to be a fast recovery or anything special about these diodes.

[Yamamaya42]

Originally Posted by timmy

On the Motorola it has 2 rectifier diodes is 1n4007 ok for this or is there supposed to be a fast recovery or anything special about these diodes.

the 1n4007 is a very old common diode that SHOULD work OK in the set, that is if you have a real one...

Problem is, over 60% of the ones out there are counterfeit junk and should not be used.

In fact, a few years back, we scrapped an entire lot of thousands of them cause they were all junk.

general rule is, anything not got from Mouser or digikey is not to be trusted when it comes to semiconductors.

as mentioned, a good choice is, https://www.mouser.com/ProductDetail...2B4kkscA%3D%3D