Regentone TV502 no video on both standards

[high_vacuum_house]

Good evening,
I have been working on this dual standard set over the last week or so and have made good progress with getting a reasonable raster. CRT is nice and bright and after cleaning the volume and brightness pots, they operate smoothly. it has a huge 23" tube.

I have decent sound on UHF and some on 405, though I have got no video drive yet. Just a blank raster. After going on a wild goose chase after printing off the wrong version of the chassis !! I think I may be near to where the fault lies. V7b is the video amplifier pentode PCL84.

The valve table shows the anode at 150 volts with the cathode at 4-5.1 volts. I measure 61V on the anode with 1.1 volts on the cathode. The resistors and inductors in the anode circuit to HT seem correct in value and when I cut the lead to the anode on the valveholder the voltage springs up to 207 volts.
My guess is that the PCL84 may be failing, and anode current is leaking to earth somehow pulling the anode voltage down. I don't think the valve is drawing too much current otherwise the cathode voltage would be much greater. The 4.7K wirewound resistor in the anode load is getting a little warmer than I like.

I have bought a new PCL84 and hopefully this will get the video back.

Christopher Capener

[slidertogrid]

Hi Christopher
Is this a KB VC chassis? there were a few alterations between the VC1 to 4. PCL84s were known to cause problems and burn up various resistors depending on the circuit and chassis. I remember the dual standard Thorn chassis (850?) could burn up quite badly when the PCL84 played up.
I will follow with interest, any chance of some pictures?

Rich

[Heatercathodeshort]

Vision detector diode O/C S/C ? J.

[dazzlevision]

See this thread for more information on the TV:

https://www.vintage-radio.net/forum/...=176222&page=3

[dazzlevision]

Originally Posted by Heatercathodeshort

Vision detector diode O/C S/C ? J.

Yes, I agree. K-B sets (and their brand name clones) of this era used STC "GD" series Germanium diodes, which I've found often go o/c with the passage of time.

[high_vacuum_house]

Just a quick update, D6 the vision detector diode (type GD12) is O/C both directions. I will have to find a replacement or something that would work. An OA91??

V7b cathode resistor was nearly half its value and has been replaced. When removed it had a hole in it pointing towards the chassis!!
The screen grid resistor which is supposed to be 3.9K measured 109 ohms. It also had a crack in it towards chassis. Must be a record for such deviation !

Hopefully when the replacement PCL84 arrives the voltage conditions around V7b should be somewhere near where they should be.

Christopher Capener

[high_vacuum_house]

Good afternoon,
Great progress was made yesterday. The final IF transformer was removed from the chassis and the can removed. I found the vision detector diode and confirmed that it was O/C both ways. I fitted an OA47 germanium diode in place of the STC GD12 diode and refitted it to the chassis. The 2 way out of spec resistors around the video amp were replaced.

On power up I was rewarded with a very good picture on UHF. I hardly had to touch any of the controls to get a full and linear picture. Switching to 405 showed that it also worked well with only a minor twiddling of the 405 line controls to get a near perfect picture. I didn't replace the PCL84 video amplifier valve after all, I decided to see if it was going to give me trouble and replace it if it did.

I gave it a 2 1/2 hour run last night on both standards and the set seems to have got better during this run. The HT current dropped approximately 20mA and the LOPT seemed to run a little cooler.

Other than a few suspicious capacitors in the timebase section, cleaning the volume pot and on/off switch and an O/C first anode resistor, the set has had nothing else really done to it except hoovering all of the dust out and checking everything looked ok.

The loudspeaker sounds a bit awful at loud output (Rattly buzz) and I think the voicecoil is rubbing. I will substitute another speaker to confirm.

Christopher Capener

[high_vacuum_house]

Here are a few screenshots of the television operating on both 405 line and 625 line standards. The camera dosen't really give the pictures justice.

The set just needs the speaker looking at and then the screening put back around the LOPT stage then the chassis being refitted properly back into the cabinet. There are a few cosmetic repairs to do as well.

Christopher Capener

[slidertogrid]

Looks good! The VC chassis was always a good one ! I have one of those narrow type speakers if yours is beyond help.
Rich

[Colourstar]

That's a super result Christopher and a very interesting (and useful) fault diagnosis. I'm delighted to see this set up and running, I had a feeling it would be a good one!

Does the lamp behind the UHF tuning scale work? I presume it only illuminates when 625 is selected?

It would be nice to find an appropriate Regentone bagde for the front. I know exactly what it should look like- it's a small shiny flat plastic insert with 'Regentone' in gold letters on a black background.

Steve

[high_vacuum_house]

The lamp behind the UHF window does work on UHF though at the moment shows up all of the dust and cobwebs behind it when lit!! There is a switch on the standards switch which is in the se'ts heater chain and switches between the lamp and a Brimistor on 405.

Christopher Capener

[high_vacuum_house]

Good afternoon,
A bit more work on the set today. I have resolved the rattly speaker fault. It was part of the laminated wood behind the speaker fret having fallen away and was loose in the speaker cone. I tested the speaker whilst it was out and confirmed the speaker is ok.

The picture shows how many components I have needed to be changed so far. Not too many really. By this date, gone are the days of loads of waxies and mouldseals. Many are ceramic tube types.

The blue capacitor was early on in the heater chain and started making its feelings of being woken up known by hissing at me hence the bulge at one end!!

Christopher Capener

[Heatercathodeshort]

TELEC ? Looks like a good quality regun. The chassis is probably a VC2 as it has a valve UHF tuner. I think the VC3 were fitted with transistor tuners.
Really reliable receivers and the Regentone version is rare. J.

[Heatercathodeshort]

The TV502 is listed as fitted with the VC2 chassis. J.

[Hybrid tellies]

What a nice looking early version of the KB hand wired dual standard set. Never seen this model before. You found some good faults and that picture does look good.