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 Return to top of page · Post #: 16 · Written at 6:22:37 AM on 14 February 2017.
BennVenn's Gravatar
 Location: Windellama, NSW
 Member since 12 February 2017
 Member #: 2061
 Postcount: 17

Thank you everyone thus far. That alignment procedure was a great read. And the schematic was far clearer than the printed copy I have.

I didn't get a chance to work on the TV last night but I did snap some pics of the underside and I'll trace out the schematic and suspect parts at work today.

If I pull the flyback pentode will it be OK to work on the chassis out of the TV? Working on my knees isn't the most comfortable.

Ben


 
 Return to top of page · Post #: 17 · Written at 4:34:23 PM on 14 February 2017.
BennVenn's Gravatar
 Location: Windellama, NSW
 Member since 12 February 2017
 Member #: 2061
 Postcount: 17

I guess not as the vert. Bias is generated from it...


 
 Return to top of page · Post #: 18 · Written at 6:10:12 PM on 15 February 2017.
BennVenn's Gravatar
 Location: Windellama, NSW
 Member since 12 February 2017
 Member #: 2061
 Postcount: 17

I've recapped the vertical stage and it's looking great. I'm injecting video into the video test point though there is no image on the tube. Just raster.

Also the spot eliminator isn't operating so I had to get creative with a discharge wand on the eht.

I'll test for video on the plate of v204A. If there is video there is it safe to assume there is a short in the crt?

Brightness control works but contrast has no effect.


 
 Return to top of page · Post #: 19 · Written at 8:20:15 PM on 15 February 2017.
Johnny's avatar
 Location: Hobart, TAS
 Member since 31 July 2016
 Member #: 1959
 Postcount: 436

Sounds like the CRT is OK.
A quick check would be to short the cathode to deck via a 10K resistor momentarily while watching the tube.
Brightness should jump up.
Generally short in CRT produces flat out bright screen with retrace lines.
Have you checked to make sure that all the valves are correct and in the right locations.
Have you checked the video detector diode for S/C. Could be located within an IF can.
You mentioned in an earlier post something about alignment.(scary).
Then I can only assume you have lots of expensive calibrated test equipment and even more knowledge.
Alignment should not be necessary except for maybe a tweak of the sound ratio detector.
Definitely not for amateurs, nor most professionals.
Get the CRO out, measure some voltages and presto it will be fixed.
JJ


 
 Return to top of page · Post #: 20 · Written at 11:29:22 AM on 16 February 2017.
BennVenn's Gravatar
 Location: Windellama, NSW
 Member since 12 February 2017
 Member #: 2061
 Postcount: 17

Diode tested ok. Grid was -500mv so I suspect the previous stages are faulty as the diode needs a signal to generate neg bias. Or the tube is bad.

With 2vpp on the grid only 20vpp was observed on the plate. This could be from lack of bias but I'd expect the plate voltage to be lower. Measured at 160v. New tube on its way.

As for the alignment, I'd like to be able to do this myself. I consider it part of the hobby. I've even started building my own vacuum tubes, glass blowing, molecular diffusion pumps etc...

My day job is a radar tech so I'm comfortable using sig gens, spectrum analysers etc. Could probably borrow some gear if I couldn't adapt what I have to do the job.

I've noticed the circuit differs from the schematic around the video amp. There are no passives inline between the IF can and the grid where the schematic shows some resistors/inductors. This was also the case when I was working on the vert stage.

I'll have to wait for the video amp tube till I can go forward.

Ben


 
 Return to top of page · Post #: 21 · Written at 1:56:10 PM on 16 February 2017.
Johnny's avatar
 Location: Hobart, TAS
 Member since 31 July 2016
 Member #: 1959
 Postcount: 436

6DX8's used to be a very reliable valve.
But you never know your luck.
JJ


 
 Return to top of page · Post #: 22 · Written at 6:08:05 PM on 16 February 2017.
MonochromeTV's avatar
 Location: Melbourne, VIC
 Member since 20 September 2011
 Member #: 1009
 Postcount: 1136

I've noticed the circuit differs from the schematic around the video amp. There are no passives inline between the IF can and the grid where the schematic shows some resistors/inductors. This was also the case when I was working on the vert stage.

Maybe your TD1 uses the earlier TE108 chassis. Give us a hoy if you want the TE108 schematic.


 
 Return to top of page · Post #: 23 · Written at 8:01:29 PM on 23 February 2017.
BennVenn's Gravatar
 Location: Windellama, NSW
 Member since 12 February 2017
 Member #: 2061
 Postcount: 17

The new tubes came in. Replaced both the video amp and the IF amp tube in the previous stage. For a few dollars, and the lack of bias on the diode it made sense to.

Powered up with a bright raster. The horisontal width was coming up short but after a few minutes it stabilised. Some fiddling with the brightness and contrast reduced the raster and made faint snow visible.

There is also very faint static in the audio so the previous IF stages are next. I might just get a complete set of tubes for the rest of the TV. I'll likely need them with the amount of use this set will get.

The dot extingushing circuit now works too.

I'll try find a balun and hook up my old nintendo and see how bad the RF chain is.

The chassis has a label with TE108F which matches up with the drawings yet the schematics are a little off. Not a huge problem. I've only found one cap that had been replaced before I got to it. In the video amp circuit too.

Did they change the PAL spec since this TV was manufactured? I don't want to chase down audio faults only to find a different sub-carrier etc...

Thanks again everyone for your help!


 
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