Magnavox Color Roundie

[tvcollector]

Well I posted results from what DaveWM asked a week ago.. He hasn't replied back to this thread.. I'm all ears.. I don't know where to go from here.. Tying to learn this stuff and if I can't fix it, than really is no point in having it.. My friend is not going to be around forever and if I can't keep these things going into the future than they will just be static items that are useless..

[DaveWM]

does the eff coil have a sharp peak?

[DaveWM]

did you go thru the horz sweep circ adj per the sams?
if so how is the shunt tube current (voltage drop across the 1k resistor, confirm the resistor value as well).

does the HV regulate well? (HV should hold constant while adjust raster brightness.

[DaveWM]

check the horz hold pot for continuity

[DaveWM]

is the line voltage 117v?

[tvcollector]

The focus coil looks fine.. The 6JE6 tests very strong.. I don't have another tube to put in it's place to see if there is any change.. I would have to order another one off eBay to do that.. The damper tube in it is a 6CJ3.. According to the sams, it's suppose to be a 6DW4.. But supposedly those are both the same tubes... Doing an eBay search most auctions list those tubes under both set of numbers.. There is no picture and HV only holds at 5000kv as I said in a previous post..

As for doing voltage checks and measuring across the pot, I will take the chassis back out tonight and do all of that..

[DaveWM]

tube substitutions are the way to go with sweep circuits not tube checkers.
if you have another working roundie use those tubes.

you may be running off frequency, a scope or freq counter would tell you that.

try unpluging the shunt tube plate cap (HV there so hang out away from anything to prevent arcing). see if voltage comes up.

make sure yoke is plugged in correctly.

[DaveWM]

https://www.youtube.com/watch?v=CiaDjKUw0nU

this should be checked on ALL vintage tv's, it is now something I do routinely.

This is a preventive maint kind of thing, as it detects a defect that can destroy shunt tubes and CRT's if there is a problem.

[timmy]

maybe its a similar problem i had with my sivertone, after checking voltages at the 6bk4 shunt come to find out there was a shorted ceramic disc in the IF section that affected the bias voltage of the shunt tube and kept the hv from rising up to where it belongs. after checking the hv adjust pot and all other related voltages come to find that the shorted ceramic cap was in the shunt tube heater string that only would have affected the crt heater, shunt tube heater, and one other that i dont remember at this point because it took years to find this problem and i dont want to look back on it because it took so long to figure out. and let me point out that i would have never have found this problem if it was not for daveWM . so if anyone is going to get to an unusual problem with one of these sets it will be daveWM. take your time and be sure to check even everything even if something dont seem related and you will probably be surprised at what you may find as the culprit all along.like me i never would have thought that a tiny .001 cap would have caused the problems i had for so long. over the 4 years i had this silvertone i replaced so much, caps, resistors, done it all.

[tvcollector]

Ok, I got the chassis out up on the table, and I'm getting only 244v at the HV regulator tube on pin 5, assuming it's the shunt tube, on the pin where the 1.5meg resistor is.. It's suppose to be 400v..

[tvcollector]

I'm measuring 0455v where the 1k resistor is on (R139) under the same tube which is HV regulator tube.. I cut the one side to measure the 1k resistor and it's only 181ohms on the meter.. Bad resistor.. Sams says voltage should be 410v, and the same on the other side of the resistor, but meter shows it a bit higher on the other side..

[tvcollector]

Adjusting the Horz EFF coil has made the current go down to around 197 - 205 ma under the HV output tube... I replaced the the 1k resistor and voltages go down to where they should be under horz reg tube..

Perhaps maybe the EFF coil could be an issue too seeing how it's right next to where the cap exploded..

Still under horz reg tube the voltages are still low at pin 5.. and HV probe at anode still shows only 5000kv

[DaveWM]

pin 5 is the ref voltage from the voltage divider off the boost.

Clearly the boost is low as it should be in the 800v range (the voltage divider of the 1.5 meg resistors and the HV adj pot sets up the 400v that should be there.

the low voltage on the pin 5 means the shunt is completely cut off, so its doing nothing (the HV adj is prob not having any effect).

I would look at the .068 caps off the eff coil, leakage there could pull down the boost voltage.

check the resistance reading of the yoke as well for the horz windings.

[DaveWM]

with the horz tube out of the socket, read the DC voltage at the plate lead (the one that says "do not measure") again WITH THE HORZ TUBE OUT OF THE SOCKET.

[DaveWM]

the 1k resistor in the cathode of the shunt must have gotten very hot at some point and carbonized to that that low (181 ohms). This means something bad wrong happened in the shunt circuit at some point. could have just been a shorted tube, but hard to say.

Did you ever read the DC voltage to ground of the filaments of the CRT?