Why no love for this GE roundie ? - Page 15 - Videokarma.org TV - Video

dieseljeep · #**211** 01-12-2015, 09:08 PM

Quote:

Originally Posted by tvcollector

Well I went to replace some more orange drop caps.. Forgot to resolder one of the resistor leads that I mistakenly unsoldered.. And the anode wire broke off.. I resolder that to were it broke off.. Powered the set up, and the HV output tube started to get super bright.. I then resoldered the resistor lead, powered up again, HV output tube lights normal, but HV does not come up now at all.. And I just test the 6JS6 and it's real weak now.. I don't have any other tubes that are 6JS6 and the RCA models have a different tube number.. Not sure if one from a CTC15 or 16 would work as a substitute to at least power up..

RCA chassis use a 6JE6 or a 6LQ6, which is a 9 pin novar base tube. A 6JS6 is a 12 pin compactron base. A 6LB6 or a 6LF6, would work.

tvcollector · #**212** 01-12-2015, 09:24 PM

Well at least I know I didn't do any damage other than blowing that tube out.. The pic still comes up, but doesn't fill the whole screen and is very dim... Those tubes are very expensive too.. Just found the cheapest, a 6JS6A that's used for $14 including shipping..

With the HV probe it measures at 16 KV.. and it takes a while for it to come up with the weak tube..

tvcollector · #**213** 01-13-2015, 05:19 AM

Pulled a 6JS6 from my Syvania set in storage.. HV comes up but now I get half a screen, about 3-4 inches of blackness on top and bottom.. Vert height control does absolutely nothing..

tvcollector · #**214** 01-13-2015, 05:40 AM

Oops.. Found the problem.. A recent resistor I tested and resoldered broke loose..

old_coot88 · #**215** 01-13-2015, 10:13 AM

Quote:

Originally Posted by Electronic M

N701 appears to be a neon bulb...They are supposed to glow orange. They were often used like zezer diodes are now. A gas regulator diode tube (0Z4 for instance) is basically a fancy version of that.

Just a minor quibble and off topic, but a NE-2 does not pull enough current to function as a supply regulator. A for-purpose tube (like the 0B2) has to shunt a large enough percentage of the supply current in order to regulate.
0Z4 is a cold cathode rectifier for car radios (though possibly it could be re-purposed as a regulator in some one-off project.

Electronic M · #**216** 01-13-2015, 01:06 PM

Not all zener diodes are directly used as supply regulators. Some are supplied a low current and used as voltage reference devices ie a they have a fixed voltage drop across them when fed a small current from a resistor connected to a larger not so fixed voltage, and there is a good chance that is how TVcollector's set uses that neon bulb.

Look for the classic 6AS7 (the 6AS7 is not a gas regulator) regulator circuit. It uses a gas regulator as a voltage reference for a 12AX7 comparator which then drives the 6AS7.

I guess I need to not pick tube numbers (that I'm not used to working with) out of memory...

old_coot88 · #**217** 01-13-2015, 06:38 PM

On a service call I ran into one of those GEs with bad color sync. It was not fixable with tubes so we shopped it. Ran the usual troubleshooting gamut with nothng out of spec. The NE-2 was lit and looked normal. Finally just replaced the NE-2 out of desperation, and the color sync and tint range popped in perfect.
Turned out the NE-2 was in the burst gate area serving GE's famous 'ringing crystal' system.
Don't remember if it was for voltage referance or for pulse keying. Probably the latter.

tvcollector · #**218** 01-13-2015, 07:44 PM

I replaced most of the orange drop caps in the HV area, two dark red ones that are .068 in the pic.. Ended up putting a .68 in place of one of them, not realizing which made the focus range different... All on the board have been replaced other than 2 on the audio side of that board.. All the caps that were replaced happened to all be good, which made no difference in performance.. So now the issue lies with the vert height range is all the way up, and after on for about 30 mins there is a very slight shrinkage drift, it's barley noticeable.. I did test with my ohm meter, the big green power resistor that's connect to the bottom of the board in the upper left of pic, and a resistor coming off of that vert height control and were in spec.. Pic shows another green power resistor and some others near the transformers.. Should I check those? I hope I don't need to check anymore things on the pc board..

HV probe also reads slightly over 22KV, that being with the HV control all the way up.. Not sure if that is a problem and if the same thing is causing the vert height issue too.. Also the focus is weird when it come to certain letters, depending on the background behind the letters, convergence is still off too.. Not sure if that would help the focus..

DaveWM · #**219** 01-13-2015, 10:08 PM

"all the caps that were replaced tested good"

which is why I preach to NOT shot gun recap this era of TV. the better approach is to simply diagnose the issue and then IF a cap is the problem replace it. there is more likely to be damage done to the old brittle boards and term strips in the process of replacement, plus there is the added bonus of creating problems where none previously existed.

the height issue is prob due to a drifted resistor in the vert osc plate supply from the boost. A quick check of that resistor will tell.

tvcollector · #**220** 01-13-2015, 10:20 PM

I think it was you that recommended to change out all the caps on the horz/vert osc board.. So I did..

I'm not sure which resistor you are talking about, and where it's located... Would it be a resistor that's somewhere along the line of the plate of the vert output tube? I'm not going to unhook one lead of each resistor on that board to figure out which one is off.. Just my luck I'll end up going through all of them before finding the culprit.. Like you said about the board and causing other issues.. I already burnt out the HV output tube..

DaveWM · #**221** 01-13-2015, 10:30 PM

i would be surprised if I suggested you replace every cap on the vert and horz, just not my way. there are a couple that generally need replacement on RCA, the diff amp grid caps (every one I have done needed them). but that is only 3 on the chroma board.

tvcollector · #**222** 01-13-2015, 10:34 PM

I'm looking at the schematic in the sams, and I see a few resistors inline with the plate of the vert output tube, R107 on board close to the vert output tube, and R112 which is located under the chassis.. should I check those out with my ohm meter?

DaveWM · #**223** 01-13-2015, 10:48 PM

it will be something like 2.2 meg, trace from the plate to the boost supply, there will be a pot and a resistor, prob a .1 uf cap somewhere in there to filter the boost. I has to go real high to be a prob, like 2x or more. check the schematic its prob isolated so can be tested in circuit.

old_coot88 · #**224** 01-13-2015, 11:23 PM

The plate load resistor of the V oscillator often drifts 'waay high. It's a problem common to all makes, both BW and color.

tvcollector · #**225** 01-13-2015, 11:34 PM

I measured from vert pot to plate and the resistor that is next to the tube is a 2.7 meg that is off quite a bit, reading around 3.2 meg. the next two along the line before plate is pretty much dead on spec and are farther away from the tube.. I'm also measuring them in circuit.. Not sure if the readings are correct.. I was told that some resistors you can measure while still in circuit.. Rather not pull anything off this board unless needed too..