a real challange? - Page 18 - Videokarma.org TV - Video

Kevin Kuehn · #1 04-12-2020, 11:19 PM

Quote:

Originally Posted by Yamamaya42

Changing the resistors did make a marginal improvement, but there is still a snowy picture.
I am guessing the RF amp is still weak. When checking voltage there it was still too low.
Should have 130v and was 107v
I then looked at the main 130v line, it TOO was low.
109v
that comes via the bleeder resistor (1.36k) from the 275v which is ay about 265v once things warm up.( close enough.
That bleeder is still getting quite warm :/
IT checks OK resistance wise, but that does not mean anything :/
gonna have to replace it.

It calls for a 17w part

closest I could find was 1.3 kOhms at 25 w

Hopefully this will get the voltage in the right area
anyway, here is how it looks with direct video input
https://www.youtube.com/watch?v=YIMi...ature=youtu.be

In an attempt to narrow things down you could try pulling rf and if tubes one at a time to see if your 135v supply increases significantly with any of them removed. When something is drawing too much current and pulling the supply down, you're not going to fix anything by changing resistors that are high or normal in value.

Kevin Kuehn · #2 04-12-2020, 11:42 PM

Another thought is the tuner and IF sections have a whole slug of 1500pf power supply bypass caps between B+ to ground. If pulling those RF and IF tubes doesn't give results, it's possible you have one or more bypass caps that are leaky. Also if you disconnect one end of R39(Sams 150 ohm) you would free up that 135v supply from the 4th IF stage forward. Something needs to give and it's simply a matter of sniffing it out. The key here is you need to divide and concur to find out what circuit is pulling the voltage down. Forget worrying about your picture quality until you find what is pulling that B+ down.

Yamamaya42 · #3 04-12-2020, 11:58 PM

Quote:

Originally Posted by Kevin Kuehn

Another thought is the tuner and IF sections have a whole slug of 1500pf power supply bypass caps between B+ to ground. If pulling those RF and IF tubes doesn't give results, it's possible you have one or more bypass caps that are leaky. Also if you disconnect one end of R39(Sams 150 ohm) you would free up that 135v supply from the 4th IF stage forward. Something needs to give and it's simply a matter of sniffing it out. The key here is you need to divide and concur to find out what circuit is pulling the voltage down. Forget worrying about your picture quality until you find what is pulling that B+ down.

well. the 6.75k resistor is definitely testing too low, by almost 1 k out of circuit, it's a 3 resistor thingy stuck in 1 pack, the other 2 check fine 12 & 93 ohms.
i got new ones coming Tue, and will replace the 6.75k first and see what happens.

Kevin Kuehn · #4 04-13-2020, 12:19 AM

Quote:

Originally Posted by Yamamaya42

well. the 6.75k resistor is definitely testing too low, by almost 1 k out of circuit, it's a 3 resistor thingy stuck in 1 pack, the other 2 check fine 12 & 93 ohms.
i got new ones coming Tue, and will replace the 6.75k first and see what happens.

Changing that one first is fine.

It's easier for me to follow these power supply voltages using the Riders schematic I posted here. https://www.flickr.com/photos/152661...7713086856613/

[edit] So if your 6.75k is part of a candohm, it's possible that part of it's winding is shorting to ground by insulation breakdown. If that's the case you'll be much further ahead by replacing all three sections. Otherwise it would be unusual for a resistor to drift down in value.

Yamamaya42 · #5 04-13-2020, 01:37 PM

Quote:

Originally Posted by Kevin Kuehn

Another thought is the tuner and IF sections have a whole slug of 1500pf power supply bypass caps between B+ to ground. If pulling those RF and IF tubes doesn't give results, it's possible you have one or more bypass caps that are leaky. Also if you disconnect one end of R39(Sams 150 ohm) you would free up that 135v supply from the 4th IF stage forward. Something needs to give and it's simply a matter of sniffing it out. The key here is you need to divide and concur to find out what circuit is pulling the voltage down. Forget worrying about your picture quality until you find what is pulling that B+ down.

there are 21 of those little bastards in there.

all still orig, I was hoping they would not be a problem, but if the new 6.750 k bleeder does not bring up the 135v to around where it should be, they are next on the list, might as well get them all, they are cheap enough.
I just hope that the resistors IN the tuner are OK, for I really don't want to go in there or have to take it out to get to them, but with the way that I have found some resistors that were almost 2x over what they should be, I DO wonder...
But finding resistors that far off does not surprise me, given that this thing spent 2/3s of it's life neglected in a dark, dank musty basement in Pennsylvania.
And I know that carbon resistors HATE THAT!

Kevin Kuehn · #6 04-13-2020, 10:40 PM

Quote:

Originally Posted by Yamamaya42

there are 21 of those little bastards in there.

all still orig, I was hoping they would not be a problem, but if the new 6.750 k bleeder does not bring up the 135v to around where it should be, they are next on the list, might as well get them all, they are cheap enough.
I just hope that the resistors IN the tuner are OK, for I really don't want to go in there or have to take it out to get to them, but with the way that I have found some resistors that were almost 2x over what they should be, I DO wonder...
But finding resistors that far off does not surprise me, given that this thing spent 2/3s of it's life neglected in a dark, dank musty basement in Pennsylvania.
And I know that carbon resistors HATE THAT!

How difficult is it to lift that 3 section candohm from the chassis, assuming it's riveted on. Doing so you may see your low resistance section move back closer to 6.750k. If that holds true, then leaving it isolated from the chassis it's likely you'd also see your 107V B+ come closer to 135v, as well as your 265V increase to 275V. It's something you could do while waiting for the replacement resistor to arrive. Keeping in mind the Candohm will heat up much more so than normal when it's physically not being heatsinked to the chassis, so this is only a short test to see if the B+ increases.

The above scenario is all based on my hunch that the one section has burned through the fish paper and is partially shorted to ground. And also requires that there's not a wire physically connecting the Candohm housing to ground.

Yamamaya42 · #7 04-12-2020, 11:14 PM

https://imgur.com/UnvD4ps

I'm gonna replace both of those resistors, i guess the 6.75k is checking a 5.43, that's prob dragging down the 130v :/

Yamamaya42 · #8 04-13-2020, 02:49 PM

Well the thing I got ( when ever it gets here ) was only about $6.50, and they say it does coils, and 5.6uh is kinda small

the ones in the set are 93-120-250 , just have to see what happens when ever it gets here, on the slow boat from China...

JohnCT · #9 04-13-2020, 04:47 PM

Quote:

Originally Posted by Yamamaya42

Well the thing I got ( when ever it gets here ) was only about $6.50, and they say it does coils, and 5.6uh is kinda small

Yep. Just checked, it will read as low as 10uh. The one I tried was 5.6uh. I'll pick a higher value tomorrow and see how it compares. I did try some capacitors today while I was playing with it, and it's pretty accurate with capacitors, and the ESR values were very close to what the Sencore Z-Meter says they are. The only thing it can't do is leakage.

Quote:

Originally Posted by Yamamaya42

... on the slow boat from China...

The longer it takes to get here, the better...

John

Yamamaya42 · #10 04-14-2020, 10:07 AM

I will have the new resistor today, and be able to try it tonight and see how things work.
I will most likely replace the 1500pf caps this weekend as well, but I'm not sure if I should touch those silly 270pf domino mica capacitors yet or not. :/

Yamamaya42 · #11 04-14-2020, 07:17 PM

yop. those damn 1500pf caps are no good.

put in the new resistor the 109V came up to 112V.

not much better.

unhooked R39 (R130 on riders/RCA) the one feeding the voltage to the IF, and it came up to 139v.

they all gotta go.

Kevin Kuehn · #12 04-14-2020, 09:36 PM

Quote:

Originally Posted by Yamamaya42

yop. those damn 1500pf caps are no good.

put in the new resistor the 109V came up to 112V.

not much better.

unhooked R39 (R130 on riders/RCA) the one feeding the voltage to the IF, and it came up to 139v.

they all gotta go.

Similarly you could remove R26 feeding B+ to the tuner, reinstall R39 and get an indication of whether it's mostly in the tuner or IF section. Of course there's the possibility that more than one caps are leaking. You can even go so far as to put a dc ma meter in series with R39 and you'll see the accumulative draw from each progressing stage. What would be very interesting is to see current draw with and without the RF and IF tubes installed. If it's the caps you'd still be seeing significant current being drawing without the tubes in. Time consuming work but very rewarding if you can narrow down the point of failure.

Yamamaya42 · #13 04-14-2020, 10:31 PM

Quote:

Originally Posted by Kevin Kuehn

Similarly you could remove R26 feeding B+ to the tuner, reinstall R39 and get an indication of whether it's mostly in the tuner or IF section. Of course there's the possibility that more than one caps are leaking. You can even go so far as to put a dc ma meter in series with R39 and you'll see the accumulative draw from each progressing stage. What would be very interesting is to see current draw with and without the RF and IF tubes installed. If it's the caps you'd still be seeing significant current being drawing without the tubes in. Time consuming work but very rewarding if you can narrow down the point of failure.

well I just ordered 21 of these, https://www.mouser.com/ProductDetail/667-ECQ-E6152KF
they SAY the the ones in there are ceramic, but I am not sure what the hell they are, I tend to think they are more like the elmenco tubular ceramic shell caps bombs that were in my CTC-16LX, they went bad as well, i took one apart and it had wax seals on the ends, and to quote Electronic M, It is usually best to assume in any tube TV that any cap 1000pF (=.001uF) and up is paper unless it is flat disc ceramic or a later film type such as a Sprague orange drop.

I just should have replaced them all at first :/

Kevin Kuehn · #14 04-14-2020, 11:24 PM

Quote:

Originally Posted by Yamamaya42

well I just ordered 21 of these, https://www.mouser.com/ProductDetail/667-ECQ-E6152KF
they SAY the the ones in there are ceramic, but I am not sure what the hell they are, I tend to think they are more like the elmenco tubular ceramic shell caps bombs that were in my CTC-16LX, they went bad as well, i took one apart and it had wax seals on the ends, and to quote Electronic M, It is usually best to assume in any tube TV that any cap 1000pF (=.001uF) and up is paper unless it is flat disc ceramic or a later film type such as a Sprague orange drop.

I just should have replaced them all at first :/

My only reservation on the wholesale replacement of those is it may complicate your alignment requirements, but you wanted to learn full blown alignment anyway.

[edit] Just looked at what you ordered. Ceramic NPO may have been a better choice, but oh well.

Yamamaya42 · #15 04-14-2020, 11:35 PM

Quote:

Originally Posted by Kevin Kuehn

My only reservation on the wholesale replacement of those is it may complicate your alignment requirements, but you wanted to learn full blown alignment anyway.

[edit] Just looked at what you ordered. Ceramic NPO may have been a better choice, but oh well.

they are unlikely to change much of anything, as they seem to be mostly noise filters on the power and ground planes, unlike the coupling caps (720 pf ) which i have, but am hesitant to put in right now, for that reason.