Still Having RCA 8TS30 Issues
 

Hi all,

Still having problems with this TV. I can't get horizontal lock when I feed a signal into it. I think the best thing to do is list what I've eliminated as possible causes. I am using the 5" CRT for testing and I have left the focus coil in place. It doesn't affect the image focus. All electrolytics and film caps have been replaced along with a couple of 270pf micas in the IF. Here's the list of what I've checked off as probably not causing the issue.

1.Signal Source. I've tried 2 signal generators, a live broadcast feed and I have fed an IF signal into the video IF in 2 places using the B&K 1077. No change in the absence of horizontal lock.
2. Tuner. As I said, I bypassed the tuner by injecting a signal directly into the IF.
3. 5" CRT. Not the cause. Same symptoms on 2 different 10BP4 CRTs.
4. Horizontal and vertical control pots. This is a concentric shaft pair. Each has been cleaned and each ohms out within specification. Just for good measure, I swapped out the control with one from a parts chassis that was cleaned and ohmed. No change in the symptoms.
5. Tubes. Every tube in the TV has been tested, replaced with NOS tubes, swapped out tubes from stock and other working TVs etc. All socket pins cleaned. No change.
6. Control pots on rear of chassis. All extensively cleaned (Horizontal and vertical position, focus, vertical linearity, height, horizontal drive) and tested for resistance. All within specs. Focus, horizontal drive pots swapped out with clean and evaluated pots from parts chassis. No change.
7. Sync Discriminator Transformer T-108. Ohmed and swapped with transformer from parts chassis. No change.
Contrast pot. Cleaned and resistance tested. Replaced with parts chassis pot. Replaced with new 10K pot rigged up separately. No change in symptoms.

So, I'm running out of ideas! I checked the signal from the horizontal oscillator at point A on T-108 and it is clean as a whistle...15.75K and a smooth sine wave. On pin 2 of the Horizontal Sync Discriminator 6AL5, it's a jumping mess of a signal that occasionally looks like an accurate waveform but it scrambles with the picture.

I've been concentrating the troubleshooting in the sync and horizontal circuits and any resistor >10% out of spec has been replaced. I even did some Shango troubleshooting by whacking a few things with the back of a screwdriver with no luck.

I know I've caused some frustration with some being a rookie who doesn't know enough about how these things work and sometimes has taken the experts through pages of messages only to find out the problem isn't in the TV but the signal generator or a bad tube. I apologize for that. I think I'm learning at least to eliminate the dumb stuff first before posting a situation that has me stumped. I'm also getting better at accurately following through with some of the suggestions that are given.

The deflection circuitry on most of these early RCAs is pretty much the same if not identical. My hope is there are some members experienced in these early RCA chassis to provide some insight.

Thanks everyone.

Chris

Listed in the SAMS is a rather detailed step by step procedure under horizontal osc adjustment / complete alignment, this sounds like what is needed as a slight retouch most likely won't work, I have not ever had to do this myself, but if it is way off, these steps may help if done as shown.

Also, the RCA service data may have more detailed steps on how to align this area.

Yes I have the service data. I can give the alignment adjustment a try. At least it'll get me to the place where I can narrow down the issue but as persistent as this has been and as many by sight and feel adjustments I've done with the controls, drive and T-108 transformer...all of my improvisational efforts to get this zeroed in have all gotten to the same place...a picture that becomes somewhat locked for a second and is kinda clear and aligned to horizontal chaos.

OK well the first step in a complete realignment is "Tune in a station and adjust the fine tuning for best sound quality. Turn the T-108 frequency adjuster on the rear until the picture is synchronized." I've turned it through its full range slowly and there's no spot where the picture syncs. It gets as close as I've gotten it before, but never full sync.

“a picture that becomes somewhat locked for a second and is kinda clear and aligned to horizontal chaos”.

Under what conditions do/did you observe the “clear” picture?

jr

The only thing I can think of, is out of tol resistors in the sync area, especially near the 6AL5 phase det, when I restored my FADA 630TS clone, many resistors were replaced, if perhaps the 2 470k resistors and the 1m are a bit off, it might upset the horz phasing, I'm sure they were replaced with 1% new in my set, as well as most of the other resistors in the sync area that did not test within 10% what they should have.

The two 470K and 1M resistors have been replaced with 1% resistors. All the resistors around the 6AL5, except for the 5K power resistor that tests spot on, have been replaced

When I fiddle slightly with the horizontal hold or the discriminator frequency or the fine tuning or the brightness pot or the contrast pot or the horizontal drive pot... Let me say when I said clear and stable...I'm talking for less than a second. It seems to change from almost think I can pull it in to awful to worse than awful back to bad almost think I can pull it in etc. I wish I could post a video. It would explain it so much better.

How strong is the vertical lock? Is it just 5 degrees or something more healthy like 1/4 turn.

Sync issues can be caused by 2 things, sync separator issues, and sweep oscillator issues. If vertical lock is weak too it indicates that the sync separator is bad or marginal. And a marginal sync input won't help the horizontal if it too is marginal. Also it's good to consider every component after the H and V sync split part of the osc circuit it feeds and scrutinize those carefully too.

Also the 630 chassis family sets lack AGC so it is possible to have contrast (which in these sets is more accurately called a manual IF and tuner gain control) set so high that the sync pulse gets clipped off at the video detector from signal overload... that's another thing to watch out for that can mess up sync.

Hi Tom...thanks for chiming in! Yes, vertical lock is stable but only compared to the horizontal. It is marginal at best and absolutely loses lock in less than a 1/4 turn. The 3 tubes in the sync circuit are NOS and I've swapped them out with multiple tubes from other TVs and from my stock with no change. I've changed only the resistors that were out of value more than 5% but I still changed 4 resistors. I was just going to change everything in the Sync circuit with 1% resistors. I've been aware of the contrast pot's influence on the signal and I've had it at conservative settings.

Exactly, on mine, I went through each and every resistor end to end, with a parameter of 10%, and any that tested out of that range was replaced, ones that were within got marked with a green ink pen, took me quite a long time to do it.

So you may still be having resistor issues.

One more thing...I don't know if it means anything and I don't know why it is what it is. One of the B+ voltage rails is low...the 135V line is at 95V only. Everything else is bang on. All new bleeder network and 2 brand new 5U4 rectifiers

I would fix the power supply first... could be the main problem.

jr

40 volts too low on that rail, could be an issue, as it does power the sync separator and 2nd sync amp, and other areas.
I had the same sort of problems, but I really doubt it is the same as you are seeing now, but what ever it is, that voltage needs to come up to around where it should be.

I do have additional low voltages. The 275v is 263v. 135v is 101v. -2.0v is -1.7v. -18v is -18.8 and the -100v is -81. What the hell is going on? I'm supposed to have 350v DC on pin 8 of the 5V4 reaction scanning tube and it reads 330v. Supposed to have 300v going into the filter choke and I've got 285v.

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

https://imagizer.imageshack.com/v2/1...922/zYMbrH.jpg

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.

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

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?

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

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.
https://live.staticflickr.com/65535/...a2bbdb4c_z.jpg

Not all of it...perhaps it would decrease the 135 volt line 10 to 15 volts. :scratch2:


jr

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.

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?

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. :sigh:

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.

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.

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!

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.

Service data says 300V DC at pin 8. I have 295V.

I could put the big, enameled wire wound back in and see if it makes a difference. The Candohm had to go...not that it was bad but they're too unreliable.

Or I do have a 10K 7W I could parallel that would get me to 1300???

Yes... 1304.

jr

On V124 (6AC7) horz osc. control tube, what voltages do you have on:

Pin 8 (plate) -- calls for 194 V
Pin 6 (G2 ----- calls for 105 V
Pin 5 (cathode)
Pin 4 (G1) ---- calls for 2 V negative

Cathode has 10 ohms to ground, so prob. not much there

I'll check those voltages later today. I've lamented my inability to show via a video what this TV is doing but if you check out shango66 today, he's working on a Packard Bell color set with AGC issues and that TV is doing the exact thing mine is doing. I know this TV does not have an AGC circuit but maybe that narrows the issue down to a specific location. Not sure.

Plate is 216 V
G2 is 86
G1 is -1.55
Cathode is...30 V DC?

30V on the cathode?!:saywhat::eek::yikes: What is the resistance-to-ground from the cathode? Print calls for 10 ohms (R194).

11.5ohm on the resistor. 30V on pin5 Here
s the topic area...

https://imagizer.imageshack.com/v2/1...922/mqEWTb.jpg

11.5Ω is close enough. The other end of that resistor ties to pin 2 which is ground. There should be solid continuity (zero ohms) from pin 2 to the chassis. Is there?