motorola vt71 ts4j 3rd if issue- it wont light

[kramden66]

Tried the tube it is not at fault. I don't think its the ground. Every tube inside lights but this one and there's no signal because of this. Any ideas? Thanks

[Kevin Kuehn]

Did you check for continuity between the tube pin sockets on top of chassis, and the solder tabs below chassis? On a wafer type socket the connection can become broken between the two wafers. Other than that, it could be a real dirty or damaged contact.

[bandersen]

It's a series strung set so the only way it's possible is if the filament pins are shorted together. Check for continuity between pins 3 and 4 on the socket.

[kramden66]

So if pin 3 & 4 are shorter that is the problem? If you pull the tube everything stays lit so it is making the series still work so must be something odd. Its not a wafer socket but one of those light brown or tan plastic type sockets.

[timmy]

Originally Posted by kramden66

So if pin 3 & 4 are shorter that is the problem? If you pull the tube everything stays lit so it is making the series still work so must be something odd. Its not a wafer socket but one of those light brown or tan plastic type sockets.

Do you have a schematic for it?

[bandersen]

Originally Posted by kramden66

So if pin 3 & 4 are shorter that is the problem? If you pull the tube everything stays lit so it is making the series still work so must be something odd. Its not a wafer socket but one of those light brown or tan plastic type sockets.

Yes, pins 3 and 4 are the filament. They must be shorted otherwise the other tubes could not be lit up with that tube pulled out.

[dieseljeep]

Originally Posted by bandersen

Yes, pins 3 and 4 are the filament. They must be shorted otherwise the other tubes could not be lit up with that tube pulled out.

The schematic shows 5000pf heater bypass caps in the IF strip. Check for a shorted cap. Also, one of the tubes in the same string may have an H-K short.
The tubes are in a series-parallel arrangement.

[kramden66]

I have a schematic and will have to check the pins. I think the 5000pf cap is a disc.

[kramden66]

I could say if you pull the 2nd if tube some go out butnot after this 3rd if. You have pull a tube after the 3rd if to get the others to go out.

[dieseljeep]

Originally Posted by dieseljeep

The schematic shows 5000pf heater bypass caps in the IF strip. Check for a shorted cap. Also, one of the tubes in the same string may have an H-K short.
The tubes are in a series-parallel arrangement.

I made a mistake on the disc caps. 250pf.
There has to be a fault on tube socket between pins 3&4. Maybe a solder splash or????.

[Kevin Kuehn]

Sorry, I completely spaced out that it's a series heater string. But that's a weird thing you have going on there.

[timmy]

So the tube that don't light up, did you try another one and did it light up on the tester if you tested it?

[kramden66]

I tried another tube and even switched it with the second if and no lighting. When I can will check the pins and socket.

[kramden66]

Pin 3 and 4 have no continuity so I checked pin resistance and pin 4 has none. I looked at the wiring and it looks like a resistor was changed. Here's something v4 going to v5 the tube that wont light v4 connects to pin 3 of v5 but v5 goes to v6 from the same pin 3. Shouldn't pin 4 of v5 be going to v6?

[kramden66]

Is a ts-18 8 inch Motorola similar so I could compare the wiring?