1950 Philharmonic 8200 Audio Issues

[vortalexfan]

Originally Posted by JohnCT

Just to be clear, when you lost the picture and sound, you were left with a blank raster with no snow, correct?

Sometimes we get lost trying to find a problem because of *too much* knowledge.

I would forget about the slipped screwdriver and troubleshoot this like it came in to my shop with no sound and no picture, so that means verifying all voltages in the tuner and IF section, and trying some tubes. Tubes become shock sensitive at times. Maybe the slipped screwdriver caused an overvoltage in one of your tube elements.

Since you seem to have a whole bag of what seem to be unrelated issues, I would again check the power supply voltages and scope them to make sure they're clean.

John

The picture went to a black blank screen, and no audio.

There are a couple of the Video IF tubes in the TV that are original to the set (they were Meck branded because they made the TV for Philharmonic).

Maybe I should try checking those tubes and replacing them with new ones?

Also I don't really have any 6AU6 tubes except what came with this tv, I do have some 6BA6 tubes which are listed as appropriate substitutes for the 6AU6.

[JohnCT]

Originally Posted by vortalexfan

The picture went to a black blank screen, and no audio.

Is there HV? A problem in the tuner or IF will still leave a raster if the brightness is midrange or higher.

Maybe tapping around the tuner is causing a sympathetic vibration somewhere in the sweep section and restoring deflection and/or HV.

Again, troubleshoot this forgetting everything you know about the TV (other than it worked after being recapped).

Originally Posted by vortalexfan

Maybe I should try checking those tubes and replacing them with new ones?

I'm not one of those guys that says never use a tube tester; I have several and find them useful to a degree. But what you need instead of a tube tester at this point is a good meter and a good scope (and an iso trans if it's a hot chassis).

I would start with the basics. Check the HV. Arc the cap of the HV rect to the cage. Scope the horiz drive to the horiz output. Check DC voltages at the CRT. If it has raster, scope the video from the detector back through the IFs.

A signal generator or a dedicated device like a B&K 1070/1077B or Sencore VA48/62 will allow you substitute drive and low level signals to see what's good and what's not.

John

[vortalexfan]

Originally Posted by JohnCT

Is there HV? A problem in the tuner or IF will still leave a raster if the brightness is midrange or higher.

Maybe tapping around the tuner is causing a sympathetic vibration somewhere in the sweep section and restoring deflection and/or HV.

Again, troubleshoot this forgetting everything you know about the TV (other than it worked after being recapped).




I'm not one of those guys that says never use a tube tester; I have several and find them useful to a degree. But what you need instead of a tube tester at this point is a good meter and a good scope (and an iso trans if it's a hot chassis).

I would start with the basics. Check the HV. Arc the cap of the HV rect to the cage. Scope the horiz drive to the horiz output. Check DC voltages at the CRT. If it has raster, scope the video from the detector back through the IFs.

A signal generator or a dedicated device like a B&K 1070/1077B or Sencore VA48/62 will allow you substitute drive and low level signals to see what's good and what's not.

John

Well I figured out what the problem was and I got it working like it should now.
My power supply caps were shorting against the chassis and some of the resistors for the Power supply circuit.

Because of how cramped it was by the power supply area of the chassis, when I originally replaced the old power supply filter caps I had to just use a free floating terminal strip for the power supply filter caps because there wasn't enough room for me to get a soldering gun into the chassis to solder the terminal strip to the chassis without accidentally burning through wiring insulation.

So apparently what the problem was that I didn't get the terminal strip situated so that it was sitting completely horizontal against the chassis so that the filter caps weren't touching the chassis or anything else near it, so when I hit the chassis with the screwdriver when it slipped the vibration of the screwdriver hitting the chassis was causing the terminal strip to move just enough to short the filter caps to the chassis and other components nearby which is why i would loose my audio and then eventually my video as well.

So I fixed the filter caps and I now have video and audio again.