Dynatron TV32 picture issues

[stubbyeddy]

I've been working on this set for the past few weeks and have made good progress, but I'm now stuck!

Before going about swapping out the valves, I've already replaced all the wax capacitors and suspect electrolytic caps. The FM radio is working well, and I have a good full bright raster on the screen. With that achieved, I decided to test it with a signal. I can achieve a good picture lock, and all controls function as expected. However, the image has a constant flicker and bending at the top, the flicker is also audible in the line output stage. I've checked the resistors and replaced a few that were out of tolerance, but no luck yet.

The only control that slightly affects the picture is the sync setting. The picture is better when set to 'direct' and more unstable when set to 'flywheel'.

I know it shares similarities with Ekco sets, but I'm uncertain which Ekco model is the closest equivalent if any...

I have a video link to show the picture https://youtu.be/ULNz_5DzpWA

Should I be thinking of valves now? I dont really work on TV's very often and this one has be a bit stuck at the moment and I didnt just want to lay blame with the valves?

any help as always much appreciated

Eddy

[Edward Huggins]

You probably know this, but a Service Sheet for the TV33 version is under the Service Data link above. As it has a FM Tuner, it is highly likely to be identical to the EKCO version. The Frame and Line stages are likely to be the same - if there are any differences, it will be in the audio stages and loudspeaker.

[stubbyeddy]

Since my first post the tuner now has died its totally deaf I was reading about some .001uf capacitors with the bands like resistors in Ekco tuners.. are these them with the back and orange? or just resistors ?

[stubbyeddy]

I have now since fixed the tuner issue, I tracked it down to a fractured resistor leg.. so I'm now back to square one with the picture issue. I have doubled checked all my work and without a scope and no circuit information that's about as far I fear I can go so if anyone can help at all it would be most appreciated, seems a shame for it go get so near yet so far!

[1100 man]

Hi Eddy,

Nice to see that another of these beasts has surfaced! Along with mine, that makes a grand total of two that have featured in forum posts over the years!

You may have already found this thread :https://www.vintage-radio.net/forum/showthread.php?t=108863&highlight=Dynatron+TV32

There is some very useful background info about the set and also various parts of the circuit diagram including the line timebase & sync circuits, so worth a look.

Also the thread about mine is here: https://www.vintage-radio.net/forum/showthread.php?t=170890

Looking at your video of the set in action looks like a sync separator issue. It could be hum getting in from the HT rail, so worth investigating decoupling caps in this area.

I generally find with most sets, that direct sync works better on a variety of signals. Flywheel sync was a great invention to cope with poor signal and aircraft 'flutter', but just gets in the way with locally generated signals from a standards converter.

Bending at the top is more likely with flywheel sync, but the set should be capable of displaying a good picture with it. However, as you have the option in this set to select 'direct', I would always use that.

It's a shame you don't have a 'scope as that makes finding this sort of fault so much easier.

Will be interested to see how you get on!

All the best
Nick

[1100 man]

Hi Eddy,

Some pictures of the circuit might be helpful!

V3,4,5 are the 1st, 2nd & 3rd vision IF amplifiers (EF85, EF80, EF80).

Interestingly, the sound has its own three IF amps, the sound take off point being just after the output from the tuner. There really was no expense spared with this set!! So a total of six valves to do the sound & vision IF stages!!

The video signal is detected by diode CD1 and passed to the video amplifier, V6a a PCF80. Another extravagance is the cathode follower for the video signal (V6b) before going to the cathode of the CRT.

The video signal is also fed to V8b, (PCF80) which is the sync separator. V8a is the white spot limiter, which is a usual inclusion in all but the most basic of 405 line tv's.

The combined line & frame sync pulses appear at pin 6 of the PCF80 and either through T4 to the flywheel sync circuit, or directly to V17, the line oscillator.

There are two decoupling caps that caught my eye which I would pay attention to. C41 (32mfd) which decouples the IF stages & video amp and C90 (32mfd) which decouples the line oscillator.

Hope that helps!

All the best
Nick

[stubbyeddy]

Hello Nick

Thanks very much for your pictures most helpful and very much appreciated. I have cracked it a long last, the fault it seems wasn't with the set at all but the converter in so much as I hadn't fed it with a video signal just used the built in test card which is where I had the problem, anyhow I decided to feed it with a signal from a DVD player with a test card DVD and the picture was fine, and then switching back to the built in test card all was well again so im not sure why it did that but its been fine ever since.

I have included some pics and a video link of the set in action, the EHT regulation is absolutely rock solid and the sound is wonderful with plenty of bass.

Thanks to everyone and especially Nick and Edward for your help and assistance.

DYNATRON TV 32 in action

Eddy

[bobbyball]

I told you that you would fix it Eddy, and my suspicions about the signal from the Hedghog were not far off!

A good picture, as expected!