Need some help on an 8TS30....
 

I've got this 8TS30 on the bench, and I should start by saying that this is the 2nd 8TS30 I've done, and about the 8th 630 chassis set....so I'm very familiar with them.....but I've run into an issue that I can't seem to get a handle on.

Started with a recap, and replaced the wirewound resistor and bad sections of the candohm in the metal box behind the transformer. Powered it up, got perfect sound but no HV. The only thing that I didn't check was the large wirewound in the HV cage. Sure enough, it was open. Now here's where things get interesting:

http://www.earlytelevision.org/pdf/r...ts-sams-54.pdf

Third page, illustrated about 10:00 to the 5V4 in the diagram, is R123....which was the open resistor. I replaced it, and variac'd it up. About 5 seconds after I hit the power at about 78 volts or so, R127B started arcing and smoking (shown on page 2, lower right). I replaced R127B with a Dale chassis mounted resistor of the correct resistance and wattage.

The first thing I thought of was that I wired the resistors incorrectly. I then stuck an untouched 8TS30 on the bench next to it, and traced out the wiring. Everything looks correct. Next, I pulled the chassis out of a restored 8TS30 to triple check my work. Again, everything I did is correct from what I can see.

Kind of at a loss as to how to proceed. Ideas/thoughts? I'm thinking there's another issue that this set has, as there's a lot of circuitry between R127B and R123....but since R123 comes right off the flyback, being open it wasn't engaging any of the HV.

If R123 is now a chassis mount dale, then what are the odds that the yoke voltage on it is enough to short thru the dale to it's chassis mounting and load the heck out of the fly?

Yeah, but he said he replaced 127B with a Dale chassis mount,which should have no connection to the yoke?

I can't see that R127B supplies any source voltages to the horizontal or vertical circuitry. Looks like it supplies negative bias to the video and sync circuits. R127B is in series with the negative voltage on the center tap of the 5U4 transformer winding - that feeds the focus coil and Ion trap, which is also in series with R128B-C and continues to ground. So basically you have a negative voltage source being divided across several resistors all in series to ground, negative bias voltages picked off to bias the video and sync circuits. Have you slowly powered back up since you replaced R127B?

I just noticed that R127B also feeds a negative bias voltage to the grid of the 6K6 audio output, but that should be isolated through a 270k resistor in series with the 6K6 grid. However the 270K(R76) may be worth investigating.

I never mentioned 127B. I was talking about R123. I think you misread my post....Though Kamakiri did not say what he replaced R123 with so perhaps I misread his post.

Sorry. I lumped R127B and chassis mount Dale together. And I took it he was now concerned with why R127B smoked. We may be missing information.

I replaced R123 with a wirewound of the same spec. That's why the set had no HV, it was open. I replaced R127B with a chassis mounted Dale resistor, but now that I think about it, I dressed the lead at a 90 degree angle, and there was *maybe* 1/4" clearance between the chassis and the resistor. Is it possible that all I did was create a gap just large enough for spark to jump to chassis ground?

I haven't replaced the resistor and powered it up since. Figured I'd verify all my work before I did.

When that thing sparked, it was like a welding arc......

The source of voltage across that group of series resistors that forms the focus coil, Ion trap, and bias network( includes R127B) , comes from the center tap of the 5U4 low voltage rectifier winding. Measuring across C1C to ground, you should have a negative voltage of less than 150.

FWIW, I would first suspect a hard B+ short-to-ground (possibly from the H.centering control or V.centering control to ground).
A hard short on the B+ line would throw a huge current draw on the 5U4 and its centertapped HV winding, and cause a large overcurrent through the resistor chain off the centertap, which includes R127B (it's the highest resistance in the chain, so it will run the hottest).

I think you probably nailed it there old-coot88. But I was sort of hoping we could at least fire up the dim bulb tester, maybe get a few voltage measurements. At least for me, most of the fun is learning how to walk through the circuit and do some basic DC troubleshooting. But I also understand that time is money. :D

Well, it's also an opportunity for a noob to see how the back-bias system works to supply negative voltages. The centertap of the HV winding, instead of going directly to ground as it normally would, goes through a resistance that's tapped for the different (-) voltages.

Troubleshooting without understanding the back-bias thing would be confusing, as evidenced in the thread.
(Of course in this case, there's also a focus circuit and ion trap whose summed resistance forms part of the resistor chain.)

Well, you've given me a place to start, appreciate that!

The set that I restored that was working fine (not this one obviously), all I did was remove and reinstall the resistor cover and look at my wiring that I did. That's IT.

Decided to watch that set for a little while, turned it on, and guess what? No raster. Removed the cover, and everything looked as it was. I didn't even pull the chassis. So now I have to figure that one out too.

#&%@ televisions. :rant:

For me, it's difficult because I've never had any formal electronics training whatsoever. Heck, I've never even had the benefit of someone in person walking me through a set step by step. It was just something that I wanted to do ever since I was a boy, so I pick it up as I go and have been doing that for the last decade or so.

I've restored close to 100 sets over the years, but every one of them was done by either recapping and getting lucky, or working through electronic principles and developing a rudimentary understanding of how things work along with problems associated with different circuits and how to resolve them.

I can recap a 630 chassis in 2-3 weeks, and my work is very precise. Hands, I've got. Diagnostic skills, not so much. Doesn't stop me from trying and learning though.

Everything with my restored 8TS30 (mentioned above) is now okay.

I disassembled and tested each resistor in the network, the wirewound in the HV cage, the resistor at the bottom of the 1B3, the doorknob cap, all of the tubes in the HV section, even the picture tube. Found not a damn thing wrong. Put it back together, and for some reason now it works.

Now back on to the problem child at hand :)

Well I hope my remarks didn't come off as sounding harsh or criticizing, that surely is never my intention here. I suppose I'm guilty of being a little too sarcastic some days. :)

I went to electronic servicing school way to late in the consumer electronics game to make any career out of it. So I ended up working many years for an industrial supplier to the weighing industry. Therefore most of my professional experience has been with DC circuits and analog to digital conversion. But in my opinion, understanding the very basics of DC and AC circuits is the key to efficiently troubleshooting these TV's, or for that matter any AC/DC electronic circuit - being able to apply Ohms law, and understanding how current flows through a circuit branch, and how that current flow creates voltage drops across the various components. In my case, seeing is believing, and so very early on I got hooked on using a scope, even when looking at simple things like power supply voltages. Where I have a major weakness is in understanding RF flow through capacitors,coils, and tuned circuits, and it's because I never really took a liking to the math involved in AC circuits. I can still look at the signals, but the results often don't make sense to me. Major stumbling block for me, that I didn't focus more on that math in my younger days.

Nah, not at all. You've helped me through a lot, as well as a lot of others, and I appreciate the patience you guys take to take concepts that you know, and "dumb them down" :)

When it comes to repair of anything, there are those who are perfectionists, those who are mechanics, and those who are just plain hacks. I'm a darn good mechanic.

One of the hardest TV repair jobs that I've ever undertaken was late 1940s TV with a stacked power supply circuit, with a humongous candohm that balanced the load between two different DC plus voltage power supplies and one DC negative voltage.

The monster candohm was open when I got the set and it was quickly located and changed out with a NOS candohm. On power-up, all three voltages were still all messed up, but in a new way. It turns out that the NOS candohm was pinched too hard in manufacture and it had a short to ground in the center.

Not hard to find, but so damned unexpected, that it was the last place I checked because I'd already changed out that bleeder network. Duh!

So, if I were you, the first thing I'd check is to verify that neither of the two resistors you replaced have a direct short to ground on either end.

The second thing I would check, would be the ohms readings on the 5V4 damper, that are in Sams. Note the '*' listing, which tells where you are to park your ground for this tube.

The final check would be to open the R123 connections to recreate the original conditions, replace the R127B, power up and see if the newest R127B gets hot. Purpose: Something else could have happened at the same time that you put in the Horiz Linearity resistor.

Since ETF also has a factory single set RCA manual for this TV, why would one use a maybe "schematic" that covers two sets that were built two years apart when the exact is available.
Sams R123 = RCA R209 and Sams R127B = RCA R232.


For the record: My nearest to formal education in electronics was the Progressive Edu-Kit in 1952:

http://www.ohio.edu/people/postr/bapix/edukit.htm

The one mentioned, along a more advanced one and with every book on electronics in the local County Library.

Hope this helps.
Jas.

I have a degree in electronics and I took it as a trade in high school. I sometimes think that I got more useful training in high school than I did in college. I only took the first year in h.s. and I remember it being all about the math of Ohm's Law and Kirchoff's Law, the use of a Simspon ANALOG meter, and logical use of your God given senses which could be nearly as important as the former(s).

By the time I found a way to make it through college consumer electronics repair was all but done with. Even component level troubleshooting with scopes and such was reduced to nearly nothing beyond power supplies. Schools are set up to help people start careers and find jobs and that dictates the curriculm's content. Thank God that both my h.s. and college teachers were "old school" guys who were around when electronics was a true science as opposed to a digital mess of plug and play stuff called electronics. An "electronics tech" of years ago bore knowledge that makes today's "electronics tech" seem like a kindergarten student in many ways.

Just take a look at the old textbooks (which by the way we all should have) and compare to something of late. No comparison. Enough to cover what is needed to unlesah the potential graduate on industrial applications which are what most schools elaborate on these days. At least community colleges or junior colleges. I unfortunately can't say what a university electronics engineering student might go experience. Probably the equivalent of what the junior college or trade school student of the 40s or 50s experienced only up to date.

Nothing at all wrong with taking a natural interest and building on it through real world experience all while having a lot of fun. And trust me, this pool of knowledge that we all are lucky to be a part of here is used by me a lot on what often is rudimentary electronics troubleshooting. We all have strengths and weaknesses. What I love about electronics is that you never stop learing. Even with backdated technology it is a constant learning experience! :thmbsp:

Brilliant :)

First check: nothing has a direct short to ground.

Second check: readings on the 5V4 are dead on.

Final check: that's next.....exactly what I had planned on doing.

Always do the tests first that are least likely to damage something. :yes:

Refresh my memory. Did you check your focus coil for internal resistance? If not do it before powering up the set.

Also, before you fire the set up, clip a DC voltmeter across R127B with the negative lead on the focus coil side.

As you bring your Variac up, when it hits 24 volts across R127B, the resistor is pulling 5 watts current draw and at 48 volts it is 10 watts and if you stay there more than a few moments you will fry your brand new 10 watt wirewound.
___________________________________

One never sees their own mistakes and a prime example is the final statement in my previous post:

Sam's R127B should be RCA's R185A (and not R232 which is next to it.)

James

Welp, the set's got audio, and makes a raster. Sort of :)

No vertical deflection, but everything else is where it should be. I tested resistances of everything in the HV/horizontal before power up and everything is where it should be. Now, on to the vertical.

Centering control moves the line about an inch.

In retrospect, the ONLY thing I can think of was that resistor simply arcing to chassis. Might not have been enough clearance there.

Okay, the set's operational :)

Turns out that the resistor WAS too close to the chassis, and it arced over. Had to end up putting a vertical blocking transformer in it as well, but everything seems fine now....except for a couple things.

The set's got inadequate width, but only by about 3/8" on either side, so I'm not so worried about that right this second. What DOES worry me is that the resistor network in the back cover is getting hot. I mean HOT. As in, I was watching the set, and I *believe* the solder on one of the resistors just melted off and POP.....the resistor dropped from the wire and I lost picture.

The contrast/AGC control also barely does anything to the picture, which is somewhat on the weak side. My other 8TS30 has full range in that department.

I don't remember any of the other 630 chassis sets I've done run so bloody hot....but then again I can't remember how much heat's back there because I've never had an issue like this.....

You need to verify your B+ voltages are what they should be at the various check points, very similar to what you just went through with the Admiral. If that resistor is burning hot, there's got to be a circuit pulling excessive current, which will show up as a lower than normal voltage at some point along the PS resistance dividing network. Voltage checks generally come first, followed by looking for circuit abnormalities causing the incorrect voltage drop.

By the way, Kevin, I very much appreciate your patience and guidance in these sets I'm having issues with.

I've repaired or recapped 26 sets over the course of 2015. Twenty six, and that's not counting ones I've shelved with issues for the time being. But for me, restoring a TV is like having a butcher remove your appendix. He can probably do it well because he's got tons of experience with the needed tools, knows what all the parts are, and is fast and skilled with his hands. Just don't expect him to have a full understanding of what all the parts are doing.....

No problem, Tim. I enjoy trying to help out, when I'm able, so it's a win-win situation. Have to admit I've only a handful of TV restorations to my credit, so I'm no veteran of the trade. I really Really appreciate the vast pool of knowledge that visits these forums on a daily basis. Not too many future generations will be able to experience the same honor. And quite honestly, it's a humbling experience, just being here in their presence.

Here's where I'd start. Sams chose not to list any voltages in the power supply area, so here's Riders references for those chimney mounted resistors.

Keep in mind that those resistors with negative voltages listed are in series with the 5U4's center tap winding going to ground. Every circuit that gets B+ is drawing current through them, but in a negative direction- the higher the B+ load, the more negative those voltages will be. It's not shown in the pictorial, but there should be something in the neighborhood of neg 55v on the left terminal of R185A.

http://i452.photobucket.com/albums/q...pszxc1jyev.jpg

Is R185a what's overheating?
And does R185a translate to R125 in Sams? If so, it's in parallel with the focus coil. If the focus coil were open, excessive voltage would appear across R185a, causing it to overheat.
Also the main B+ would drop some, likely causing insufficient width.

Nope.
R185A was what I referenced from the Riders chimney wiring pictorial - it's equivalent to R127B(230 ohms) in Sams. Yeah, it's confusing as heck going back and forth between the two source materials, but I wanted to show the voltages as pictured on those resistors in Riders. The 1800 ohm resistor in parallel with the focus coil is not in the chimney. The resistors as shown in Sams that appear in the Chimney, are R127a,b and R128a,b,c. I went back and added the resistor values in red to the Riders pictorial.

So which resistor specifically is overheating?

No clue. I don't think he's spilled the beans. :D

Captain, if your sick of this one and nothing prevents either of us from going to the meet I'd be willing to take it off your hands....especially if it is the one with the blue tinted screen (that thing is wicked awesome looking).

It's R127B again, but R127A's getting pretty toasty too. And no, it's not the one with the blue screen....although I've been thinking of selling that one, actually ;) . This one belongs to Rodmonster, I'm doing him a gigantic favor.....

No, no, I didn't get sick of the set....we just had a rare couple of 60 degree December days in Buffalo, so I wanted to take full advantage of it to get some work done on the TV hauler.

This is the picture I got on the screen just before the "meltdown". The resistor itself looks okay, admittedly I didn't ohm it out yet. The raster is full width, but the picture is not.

OK lessee if I got this right now.
R127B corresponds to Riders R185A (the right-hand section of the big honkin' chimneyed resistor shown in post# 26). If so, it should measure 230 ohms with one end disconnected.
If it's signifigantly higher than 230 ohms, it would definitely overheat as well as drop the main B+ a bit.
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Is there any chance the replacement was swapped end-for-end when installed? If so, it would explain the overheating since the other section is 1360 ohms. (it would probably explain the width anomaly too)

About a 99% chance that's not the case. When I started having issues that prompted this thread, I checked the wiring against two other 8TS30s, one unrestored and one I restored about a year ago. Both were a match.

So.. have you physically disconnected one end of R127B and ohmed it for 230 ohms? And verified that circuit-wise it's connected correctly (i.e., one end going to the ion trap and the other end to the 93 ohm resistor R128C)?

You got it. Now if we could only get our field representative to take a couple measurements...;)

:DSotta like gettin' Hannibal over the Alps.
Just Kidding!!!! :p:

I'm glad YOU said that. :D

Geeze louise....I gotta work for a living too, y'know! So nyah ;)

Since one end of the resistor's already disconnected, that made it easy. 234 ohms. I knew it would be because I replaced it earlier, unless it fried, which it didn't.

I'll do some wire tracing when I finish work for the day......

Sollder that puppy back up and lets get a voltage measurement acrost it. Plus it would be cool if you could make a video of solder melting off it's terminals. ;)