I’m Back! Pilot TV37

[Phil Nelson]

Originally Posted by Chris K

I don't want to power the chassis up and sacrifice tubes that are burning hot. Any suggestions as to where I can begin a basic troubleshooting so I can find where I screwed up?

The Sams service manual has a complete resistance chart for the TV-37:

http://www.earlytelevision.org/pdf/p...sams_62-16.pdf

Checking the resistance at every pin of every tube is tedious, but it is done with the TV powered off and it doesn't require great diagnostic skill. If you find a big discrepancy between the ideal resistance and the measured resistance, that might point you in the right direction.

For each pin, you are basically checking whether its resistance value is more than 20% above or below the ideal value given in the chart. Look carefully at the little notes at the bottom of the chart.

Now, it's possible that you'll take all those measurements and find nothing amiss -- but that, too, is useful information. You just confirmed a bunch of things that are correct and can be crossed off the trouble list.

Phil Nelson
Phil's Old Radios
https://antiqueradio.org/index.html

[jr_tech]

Likely a heater cathode short or wiring error in the series string heater connection of one of the unlit tubes.

jr

[Chris K]

Originally Posted by Phil Nelson

The Sams service manual has a complete resistance chart for the TV-37:

http://www.earlytelevision.org/pdf/p...sams_62-16.pdf

Checking the resistance at every pin of every tube is tedious, but it is done with the TV powered off and it doesn't require great diagnostic skill. If you find a big discrepancy between the ideal resistance and the measured resistance, that might point you in the right direction.

For each pin, you are basically checking whether its resistance value is more than 20% above or below the ideal value given in the chart. Look carefully at the little notes at the bottom of the chart.

Now, it's possible that you'll take all those measurements and find nothing amiss -- but that, too, is useful information. You just confirmed a bunch of things that are correct and can be crossed off the trouble list.

Phil Nelson
Phil's Old Radios
https://antiqueradio.org/index.html

Hi Phil...thanks so much for your input! I know these questions will demonstrate my minor league status but bear with me! I have the chart. Tubes in the sockets or out when I measure? Measure resistance to ground except where indicated otherwise?

[Phil Nelson]

Leave tubes in their sockets. Note #3 under the charts says the resistance is measured “from the common negative unless otherwise indicated.” The little footnotes under the resistance chart specify alternate connection points for a few measurements.

Phil Nelson

[Chris K]

Originally Posted by Phil Nelson

Leave tubes in their sockets. Note #3 under the charts says the resistance is measured “from the common negative unless otherwise indicated.” The little footnotes under the resistance chart specify alternate connection points for a few measurements.

Phil Nelson

Filling in an Excel spreadsheet with the listed values and actual values. I'm doing it by tube number that starts in the front end with the 3 12AT7s and I've already found wacky values. I'll post it when I'm done. Maybe someone with good investigative skills can tell me what I'm missing

[Phil Nelson]

Also note jr_tech’s comment about checking the heater connections throughout the tube strings. On page 2 of the Sams schematic, the diagrams at the far lower left show all those heater connections.

You can see that pin 7 of V20 connects to pin 8 of V21, and so on down the line. Using your ohmmeter, you can check these connections for continuity, working from one tube to the next.

Phil Nelson

[Chris K]

Originally Posted by Phil Nelson

Also note jr_tech’s comment about checking the heater connections throughout the tube strings. On page 2 of the Sams schematic, the diagrams at the far lower left show all those heater connections.

You can see that pin 7 of V20 connects to pin 8 of V21, and so on down the line. Using your ohmmeter, you can check these connections for continuity, working from one tube to the next.

Phil Nelson

Got it Phil...working through it

[Chris K]

Originally Posted by Phil Nelson

Also note jr_tech’s comment about checking the heater connections throughout the tube strings. On page 2 of the Sams schematic, the diagrams at the far lower left show all those heater connections.

You can see that pin 7 of V20 connects to pin 8 of V21, and so on down the line. Using your ohmmeter, you can check these connections for continuity, working from one tube to the next.

Phil Nelson

OK I measured all of the resistance values as instructed in the Sams. I checked filament continuity in the strings and they are all fine with no breaks. I thought I would start describing the situation with the 35W4 negative rectifier as that's one of the first power tubes to come off the ballast. All of the pin resistances are fine except for pin 5 that's supposed to be 33k and it's unreadable jumping all over the place from 0 ohms to 4 meg when I put the probe to it. Pin 5 of it goes to pin 8 of the HV oscillator 25L6 but all of the pin resistances on the HV Osc. are close to the table values. Then on the HV rectifier 1B3, there are many pins off value. Pin 4 is bouncing all over like pin 5 of the 35W4 and pins 2 and 3 that are supposed to give infinite values are reading low ohms; 21 for pin 2 and 0.3 for pin 3. Arughhhhhh! Does that give you any enlightenment? I did replace all of the electrolytics. The TV worked after I replaced them...sorta but these most recent issues appeared after replacing about 15 resistors.

[Electronic M]

I would ignore the 1B3 HV rect. It's heater is powered by a winding on the HV osc coil, and thus not part of the series heater chain you're trying to troubleshoot.

If you are using an auto ranging meter try manually setting the range...I've found if there's capacitance on a circuit that I want to measure resistance on then that capacitance and the auto range form a sort of oscillator circuit that prevents any kind of meaningful stable reading.

Another troubleshooting option is to hook the set to a variac at 60V, wait 2 minutes for stable heater operation then check voltages along the chain... Voltage drops across heaters should be roughly half of their normal values at half of normal line voltage...
When I have an open heater in a series set you can flip a coin whether I troubleshoot it using voltage or resistance.

[Chris K]

Originally Posted by Electronic M

I would ignore the 1B3 HV rect. It's heater is powered by a winding on the HV osc coil, and thus not part of the series heater chain you're trying to troubleshoot.

If you are using an auto ranging meter try manually setting the range...I've found if there's capacitance on a circuit that I want to measure resistance on then that capacitance and the auto range form a sort of oscillator circuit that prevents any kind of meaningful stable reading.

Another troubleshooting option is to hook the set to a variac at 60V, wait 2 minutes for stable heater operation then check voltages along the chain... Voltage drops across heaters should be roughly half of their normal values at half of normal line voltage...
When I have an open heater in a series set you can flip a coin whether I troubleshoot it using voltage or resistance.

So nothing is burning up but I've got no horizontal deflection. I need to start looking through that circuit. All tubes are warm/hot.

[Electronic M]

Good to see light on the screen and the heaters working correctly again.

I'd probably check voltages on the horizontal tubes against the schematic values. Discrepancies there should point you towards the issue.

[Chris K]

Originally Posted by Electronic M

Good to see light on the screen and the heaters working correctly again.

I'd probably check voltages on the horizontal tubes against the schematic values. Discrepancies there should point you towards the issue.

Will do...thank you Tom

[Phil Nelson]

Don't play the TV for any length of time with that brilliant line showing on the screen. It may burn a permanent dark image in the phosphor.

Phil Nelson

[Chris K]

Quick update. The Pilot just died. I have no idea what happened. When I bring it up on a 60W bulb/Variac, there’s no light on the bulb and the tubes stay cool. I’ve got AC voltage coming out of the ballast but no voltage on the heater strings. I found a cold solder joint on the single 47v electrolytic and fixed that but nothing. I checked the voice coil for continuity and it’s fine. I have a NOS crt I tried and it’s still dead. The filament strings have continuity all the way through. It’s just dead as the proverbial door nail and I’m completely stumped. Jesus these things are hard for me. This is supposedly one of the most basic and easiest sets to work on and mine has mostly new parts and I’ve gone over everything I know to check and nothing. So frustrated.

[bandersen]

Check for continuity on the AC plug with the power switch turned on. Also, 60W is pretty low for a TV - you're really starving the set of power. Try 200W or bigger.