Need some help on an 8TS30....

[Kamakiri]

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.....

[Kevin Kuehn]

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.

[Kevin Kuehn]

Originally Posted by Kamakiri

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.

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.

[old_coot88]

Originally Posted by Kevin Kuehn

...It's not shown in the pictorial, but there should be something in the neighborhood of neg 55v on the left terminal of R185A.

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.

[Kevin Kuehn]

Originally Posted by old_coot88

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.

[old_coot88]

So which resistor specifically is overheating?

[Kamakiri]

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.....

[Kevin Kuehn]

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.

[Electronic M]

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).

[Kamakiri]

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.

[old_coot88]

Originally Posted by Kamakiri

It's R127B again, but R127A's getting pretty toasty too.
....... The resistor itself looks okay, admittedly I didn't ohm it out yet.

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.
----
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)

[Kevin Kuehn]

Originally Posted by old_coot88

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.

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

[old_coot88]

Sotta like gettin' Hannibal over the Alps.
Just Kidding!!!!

[Kamakiri]

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.

[old_coot88]

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)?