Newbie's First Questions RCA TS 721 Restoration

[Chris K]

Originally Posted by Yamamaya42

I have not seen that he has made the voltage tests yet, are the all in spec?

No pin voltage tests yet. I'll do all of them tonight. Stand by!!!!! Thanks for the guidance and help!!!

[Chris K]

OK...here we go. Man, is this screwed up! First I measured all of the resistors in the schematic in around the 6K6, 6AT6 and the 6AL5. All 3 tubes are fresh replacements testing good. I'm using the Riders parts list for identification. I won't list the rated resistance, just what I get. The ratings are on the schematic.

R179 496k R180 8 Megs R181 103k R184 484k R185 1.1k

Now the pin voltages. This is where it's a mess. All volts are DC unless AC is indicated. The pins will be identified as P1 or P2 for Pin 1 or Pin 2.

6K6: P1 No Pin P2 6.3V AC P3 -67.4V P4 -67.5V P5 -14.3V P6 -15.1V P7 No Volts P8 No Volts. Oy Veh!

6AT6: P1 through P3 No volts P4 6.2V AC P5 -3.1V P6 -0.67V P7 58.7V

6AL5: No volts on any pin except 6.3V AC on pin 3

Jesus...what a mess. Maybe I should just throw it out and restore another Philco!

Thanks
Chris

[Chris K]

I think I may have found something. R171 connected to P6 of the 6AT6 is supposed to be 6.8Meg and it's reading 95k in circuit

[Chris K]

Never mind...out of circuit it's 7 meg

[Yamamaya42]

this is the tube voltage chart from the SAMs for the RCA 630ts which is very close.

http://suzaku.live-evil.org/sound-volt.jpg

Ref V14 15 16

it's normal to see almost no voltage aside from heater on the 6AL5

the 6AT6 also seems OK, pin 7 may be lower than what is said, but mot likely not an issue.

what is WEIRD here is the 6K6GT,,
You should be only be seeing negative voltage on pin 5, if pins 3 & 4 are negative then something is VERY wrong, especially if you have a good strong +225 bias on the far side of that 1k power resistor feeding it.

[Chris K]

Originally Posted by Yamamaya42

this is the tube voltage chart from the SAMs for the RCA 630ts which is very close.

http://suzaku.live-evil.org/sound-volt.jpg

Ref V14 15 16

it's normal to see almost no voltage aside from heater on the 6AL5

the 6AT6 also seems OK, pin 7 may be lower than what is said, but mot likely not an issue.

what is WEIRD here is the 6K6GT,,
You should be only be seeing negative voltage on pin 5, if pins 3 & 4 are negative then something is VERY wrong, especially if you have a good strong +225 bias on the far side of that 1k power resistor feeding it.

There's a wiring issue with one of the electrolytic caps...C131. I've got -75V DC all over the place here. Let me recheck what I did.

[Yamamaya42]

then you should have a dead set :O

gonna have to trace the main bias path from the 5U4 heater through the filter -> horz center pot -> vert center pot -> focus coil - > bleeder network to try to see where it's getting lost, and hope that it's not a unreplaceable part like an open focus coil.

[Chris K]

Originally Posted by Yamamaya42

then you should have a dead set :O

gonna have to trace the main bias path from the 5U4 heater through the filter -> horz center pot -> vert center pot -> focus coil - > bleeder network to try to see where it's getting lost, and hope that it's not a unreplaceable part like an open focus coil.

Yes, I did the 225V DC trace from the 5U4 to C131 and out many times over when I replaced all the electrolytic caps. I currently have a mix of the correct DC voltages and this odd negative voltage. Fortunately, the Riders comes with a wiring diagram which has come in handy many times during the initial stages of this project.

I don't think the focus coil is open because moving it does what it's supposed to do on the CRT but, as I've displayed here several times in this thread, what the hell do I know

So my plan is to meticulously retrace the 5U4 DC output checking voltages along the line until I find my screw up. My wife and I are leaving for a well deserved vacation tomorrow so, unless I act on an insane instinct to bring the TV and all of my equipment to Cape Cod, I probably won't have anything to post on this project for the next 8 or 9 days. I appreciate all of the help the forum members have offered to this point and I hope everyone who have been so generous so far will stand by until I pick this up again in a week or so. At least now I know, thanks to you, it's a major and possibly single issue of a miswiring or something easily corrected. I hope!

[Yamamaya42]

I literally spent a few months bringing my Fada 895 (rca 630ts clone) back from the dead, starting with just a chassis, 12LP4 and safety glass faceplate, which spent a large part of it's life nonfunctional custom built into a wall in my Grandparent's home in Pennsylvania, early 70s to late 90s, when they sold it and I removed it and had it shipped to my home, chassis was slightly damaged in the move, it was then kept in storage for more years till I was ready for the challenge to restore it.

I guess the reason the 12LP4 is so strong is that it ha not been used since the 70s.

I spent many many hours going over documentation working out how the silly thing worked!
Including RCA630TS Service manual, rca_630ts_sams , both sams and riders for Fada 895.

The thing is a pain to work on, but worth the time and effort!

[Notimetolooz]

The resistor wattages are based on what the voltages (and resistance) should be. A one watt resistor could be used if the actual dissipation is 0.625 W but it will run hotter than a 2 W.

If you plan to work on more TVs in the future a tube tester might be more economical that replacing all the tubes at the start. Also that way you don't throw out tubes that may have worked fine in the TV.

The forum will be here when you get back.
Stay away from sharks.

[Chris K]

Originally Posted by Notimetolooz

The resistor wattages are based on what the voltages (and resistance) should be. A one watt resistor could be used if the actual dissipation is 0.625 W but it will run hotter than a 2 W.

If you plan to work on more TVs in the future a tube tester might be more economical that replacing all the tubes at the start. Also that way you don't throw out tubes that may have worked fine in the TV.

The forum will be here when you get back.
Stay away from sharks.

Water up there is in the high 50s. It'll be Land Sharks I'll need to be careful of!
A tube tester is on my wish list...absolutely and I love these old TVs from the late 40s and early 50s. They are built like tanks!

[Yamamaya42]

The +225v is critical for the horizontal and vertical deflection, and thus HV, if you have something on the screen as you mention, then the +225v line has to be working partly, but there must be some error along the line of it in it's point to point wiring, won't be easy to track down.

[Notimetolooz]

It isn't that bad.
The 6K6 voltages can all be explained if R185 is connected to the -85V supply point instead of the +225V.
The 6AT6 could be something different. The grid pin 1 should be a bit negative, if it is near zero it could be passing too much current. That could cause pin 7, the plate, to be pulled too low. Check R180. Another test would to measure the voltage on pin 7 if you remove the 6AT6, it should go to about 225V. Check R179.
It would also be a good idea, one that is always a good idea to do early, is to measure the voltage supply points in the power supply. +225V, +150V, -3.5V -14V and -85V.

[Chris K]

Originally Posted by Notimetolooz

It isn't that bad.
The 6K6 voltages can all be explained if R185 is connected to the -85V supply point instead of the +225V.
The 6AT6 could be something different. The grid pin 1 should be a bit negative, if it is near zero it could be passing too much current. That could cause pin 7, the plate, to be pulled too low. Check R180. Another test would to measure the voltage on pin 7 if you remove the 6AT6, it should go to about 225V. Check R179.
It would also be a good idea, one that is always a good idea to do early, is to measure the voltage supply points in the power supply. +225V, +150V, -3.5V -14V and -85V.

Everything coming off the bleeder resistors is perfect

[Chris K]

Originally Posted by Yamamaya42

The +225v is critical for the horizontal and vertical deflection, and thus HV, if you have something on the screen as you mention, then the +225v line has to be working partly, but there must be some error along the line of it in it's point to point wiring, won't be easy to track down.

I've been in this chassis and traced the wiring for so long, I feel like I know it by heart!