Still Having RCA 8TS30 Issues

[Chris K]

Here is the power system. The voltages written are what I've measured.

[Yamamaya42]

First, don't take what is in the RCA service manual as absolute, the will be variations, I worked with that and the SAMS, and found that thing are sort of halfway between what is shown in both, don't look at what is listed in them an what voltages MUST BE, more sort as a guide.

And since ground is not AT ground in this set, but going through a bleeder network to produce negative voltages, any problem in one or more of them on the chain like the 135v line or more will tip everything out of balance and give weird voltages and odd results, like bandersen found out when he accidentally turned his focus coil into a battery by dunking it in Evapo-Rust.

something has upset the balance of your power system.
most likely in the 135v line.

[jr_tech]

Indeed! If the two resistors in the 135 volt divider are in spec, I would be checking all circuits connected to the 135 volt supply for high current draw.

jr

[Chris K]

The 1360 ohm was replaced with a 1.5k 25W resistor. Closest I could get in that watt range. That wouldn’t account for the 30-35v loss in the 135v line would it?

[Yamamaya42]

That could be the problem, however, it does not rule out an issue with the 135v line.
It's unusual for the high power wire wound resistors to go bad, it does happen but it's rare, it is much more often for the candohm resistors to fail before the 25 watt ones, were yours really bad? And what were all the other bleeders replaced with?

However, since you already have the 1.5k 25 watt, what you might think about doing is getting a 12k 25 watt, and hook it in Parallel to the 1.5k, this will get you 1333.33, much more close to the original value. https://www.mouser.com/ProductDetail...E0g4acOQrU8%3D

[bandersen]

Yes ^^^ but you can use a much smaller wattage. The power will divide in the same ratio as the resistance.

A 12K rated for 3 watt or better will do. If you don't have one handy, use a 10K just to see what effect it has.

Here's how I did a 721TS recently. I paralleled a 1500 with 5000 to get the required 1125.

[jr_tech]

Originally Posted by Chris K

The 1360 ohm was replaced with a 1.5k 25W resistor. Closest I could get in that watt range. That wouldn’t account for the 30-35v loss in the 135v line would it?

Not all of it...perhaps it would decrease the 135 volt line 10 to 15 volts.


jr

[Yamamaya42]

It should be interesting to see what the full output of the 5U4Gs are before going into the bleeder network, as in from pins 8 (cathode positive point ) to the -100v point (transformer center tap) , should be at least 400v, if not more reading at those points.

[Yamamaya42]

Originally Posted by bandersen

Yes ^^^ but you can use a much smaller wattage. The power will divide in the same ratio as the resistance.

A 12K rated for 3 watt or better will do. If you don't have one handy, use a 10K just to see what effect it has.

Here's how I did a 721TS recently. I paralleled a 1500 with 5000 to get the required 1125.

How common is it for the larger 25w resistors to be bad? The tested OK on mine a few years ago, so I left them in. only 1 section candohm resistor tested funny at the time, which I bypassed, I should have done all 3 sections, as I now suspect the other 2 are starting to fail as well, as when the sound is at max,the picture shrinks horizontally. Granted this set had no sound OEM, but that sound not be an issue, as it has the same power system in it as TVs with sound originally.



For now, I have the audio output pulled and am using a cheap LM386 amp for sound till I address the candohm resistor issue, but, do I replace ALL the bleeder network preemptively, or leave the larger 25w resister in if it still seems good?

[Electronic M]

The candohms are not uncommon to find shorted to chassis or open, and the tubular ceramics do open sometimes (changed an open one on a 721TS this spring).

One small concern I have is your mention of bypassing a resistor section...If it wasn't an end section and it isn't open or more than 10x above its rated value it's hard to bypass it without the original throwing things off or extremely delicate surgery to force open the original.

Personally the B+ voltages are close enough that I wouldn't be chasing them as a cause of any other issue.

[Yamamaya42]

Originally Posted by Electronic M

The candohms are not uncommon to find shorted to chassis or open, and the tubular ceramics do open sometimes (changed an open one on a 721TS this spring).

One small concern I have is your mention of bypassing a resistor section...If it wasn't an end section and it isn't open or more than 10x above its rated value it's hard to bypass it without the original throwing things off or extremely delicate surgery to force open the original.

Personally the B+ voltages are close enough that I wouldn't be chasing them as a cause of any other issue.

it was an end section of the candohm that tested rather high at the time and was bypassed, forget which end. :/
I should have done the whole thing.

[Yamamaya42]

My set, the -100v tests at -86v and it changes when i adjust the focus, so I dont think your -81v is an issue.

http://suzaku.live-evil.org/0613242200a.mp4
Mine
it was the 6750 ohm part on mine that was replaced.

[Chris K]

Thanks everybody for the discussion. Couldn’t work on the tv today “new hot tub delivery!!!!) but I’ll be back on it tomorrow. My hunch as I’ve said is this just doesn’t look like an issue caused by a low but stable voltage. It seems more like intermittent noise although it’s not the tuner. We’ll find it just like my RA-103 that was on and off my bench for a year until you guys led me to the problem.

[Chris K]

Originally Posted by bandersen

Yes ^^^ but you can use a much smaller wattage. The power will divide in the same ratio as the resistance.

A 12K rated for 3 watt or better will do. If you don't have one handy, use a 10K just to see what effect it has.

Here's how I did a 721TS recently. I paralleled a 1500 with 5000 to get the required 1125.

That takes me back...the 721 was my first serious restoration several years ago. I need to revisit that one. Ended up running composite video because I couldn't get picture and sound through the tuner and RF. But first RCA things first!

[Chris K]

Originally Posted by Yamamaya42

That could be the problem, however, it does not rule out an issue with the 135v line.
It's unusual for the high power wire wound resistors to go bad, it does happen but it's rare, it is much more often for the candohm resistors to fail before the 25 watt ones, were yours really bad? And what were all the other bleeders replaced with?

However, since you already have the 1.5k 25 watt, what you might think about doing is getting a 12k 25 watt, and hook it in Parallel to the 1.5k, this will get you 1333.33, much more close to the original value. https://www.mouser.com/ProductDetail...E0g4acOQrU8%3D

The 1360 was replaced with a 1500, the 230 with a 240, 6750 with 6800 and the 93 with a 100 ohm.
I guess they're all high.