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Old 19th Jan 2024, 5:03 pm   #1
G8vsjDave
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Default Fun with a Rigonda VT100m

For some time I had been on the look-out for one of those 6 inch Rigonda VL100 televisions, and just before Christmas a very sorry looking specimen came my way. It looked as though it had been stored in a damp place because there was rust on the internal metal work. I had the circuit diagram and a copy of the April 1984 issue of Television in which there was an article about servicing the VL100, so I began to play.
Having removed the metal cover I applied 12 volts to the rear connectors having first worked out which was positive. The result was nothing. While having a quick poke around the power supply circuit I noticed a wire hanging from the output transistor (T27) and a closer inspection revealed the wire was complete with the power transistor’s pin. To make matters worse a gentle tug on the other wires, caused another wire and pin came away.
The Television article said a TIP32 would work but not having one to hand, I fitted a general purpose silicon PNP power transistor – still nothing came out of the power supply.
A check on the other two transistors in the stabiliser control circuit showed one to be dead and the other with a broken connection. The soldered joint was still holding the wire from the transistors ‘leg’, but the wire had rotted through just above the component side of the board. I replaced both transistors with generic silicon types and powered up – with no results.
Studying the circuit I noticed a series C/R from the un-stabilised voltage input to the base of TR26 (see image 1) which I thought would provide a start-up pulse to get the circuit stated. On replacing the 10uf capacitor, I was rewarded with a hiss from the speakers and a working power supply. My victory however was short lived, because the next time I powered up, nothing happened. I eventually realised that the 10uf capacitor was not discharging so there was no start-up pulse. I guess the old Germanium transistors leaked enough to provide a discharge path. My solution was to fit a 24k resistor across the capacitor.
The ‘hiss’ from the speakers varied when the tuning control was adjusted, so I concluded the tuner and IF strip was probably Ok. Bringing my scope probe towards the LOPT showed no response and this was traced to the line oscillator (TR23) having an open circuit connection (rotted leg,) and on replacing this I found I had line drive. The line output transistor was found to be Ok and I had a nice pulse showing on my scope, but I soon found the line output transformer had an open circuit secondary.
Turning to the frame circuit I found another rotted transistor connection but this time I was able to remove and clean the transistor which then got the frame working.
I enjoyed looking at this set and repairing what I could. I managed to take the old LOPT apart and count the number of turns on the primary but unfortunately I broke the ferrite so re-winding is not an option. I will put the set on the ‘on going’ pile in the hope of one day finding a transformer that might be compatible for a transplant. If anyone has such a transformer that MIGHT work please PM me.
Dave
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Old 20th Jan 2024, 11:37 am   #2
Welsh Anorak
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Default Re: Fun with a Rigonda VT100m

It's so dispiriting to get something almost working only to fall at the last hurdle!

The LOPTs on these were always vulnerable and led to most sets being scrapped.

An O/C winding is a challenge, and the size of the transformer doesn't help. However you just might find someone with a faulty LOPT that you can salvage the ferrite core from and rewind it. Worth a 'wanted' request?
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Old 20th Jan 2024, 12:32 pm   #3
slidertogrid
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Default Re: Fun with a Rigonda VT100m

These were fun even back when they were new! When I was 15/16 through a third party I did a lot of repairs for Woolworths and saw lots of these and the "Starlet" which was a larger screen and quite a nice looking little set. The circuit diagram was a terrible copy, tiny and didn't always agree with the set. I always had a few VL100s awaiting LOPTs it was a very common fault.

Woolworths could get parts from Rigonda but it took ages, this resulted in customers complaining (to them thankfully!). I had a word with the guy that dealt with the repairs and suggested getting some LOPTs for stock. Eventually I received a box of 50 all wrapped in brown wax paper in a partitioned box. I used a few but not too long afterwards gave up the job which I did freelance as I had left school and got a 'proper' job. All of the parts and a few scrap sets that had been dropped remained in my old workshop for a few years until my parents moved house. Then the whole lot including lots of D.S mono and colour spares used valves etc were loaded into my car and taken to the dump... Lesson learned!
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Old 20th Jan 2024, 1:12 pm   #4
hamid_1
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Default Re: Fun with a Rigonda VT100m

What a shame. I also have a Rigonda VL100M that died in 1990 while I was watching it. Suspected LOPT failure - I could hear line whistle (back then) but no EHT. At the time, I asked a TV repair place about obtaining a replacement LOPT and was told they were no longer available. That was in 1990. I kept the set since then, just in case another LOPT turns up. I'm still waiting...

I do have a couple of the later models 402 which seem to have similar circuitry including the top-hat Germanium transistors but in a different style of cabinet. At least one of those sets still worked when I last tried it. The LOPT looks similar to the VL100M though unfortunately it's not interchangeable.
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Old 3rd Feb 2024, 12:27 pm   #5
G8vsjDave
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Default Re: Fun with a Rigonda VT100m

After my last post regarding my Rigonda VL100M, I was contacted by Greg, a member of our Forum, who offered me a LOPT from one of those generic Chinese 5.5 inch televisions that were sold in the UK under several names, and I believe the model number to be 333TAVR. I was able to find the circuit diagram of the ‘donor ‘ television (see attachment) and Greg also sent me some information about the transformer connections.
Using a piece of matrix board, I made a board to hold the transformer and some auxiliary components as used in the original Chinese design and started to wire it in. I decided to use the original Rigonda line output transistor as this was OK and I had previously tested the line driver stage. I used a separate power supply for the new LOPT stage and slowly wound up the voltage.
At about 8 volts to the LOPT stage, I had a nice flyback display on my scope and all was looking good, I continued to increase the voltage and was pleased to see a raster on the screen which unfortunately faded after a few seconds and I was unable to get it back. I then noticed the current to the new LOPT stage had dropped and I eventually realised the tube heaters had become open circuit. When I checked my connections I realised I had connected the LOPT heater winding to the wrong side of the heater’s current limiting series resistor and I guess the Rigonda tube had a low current heater.
I’m not giving up though – anybody got a scrap Rigonda VL100 with a good CRT? (See ‘wanted’).
Dave
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Old 3rd Feb 2024, 4:26 pm   #6
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Default Re: Fun with a Rigonda VT100m

Sorry folks. Attachment here.
Dave
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Old 3rd Feb 2024, 10:42 pm   #7
Maarten
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Default Re: Fun with a Rigonda VT100m

The modern CRT uses an 11-12V heater. What's the correct voltage for the Rigonda? If lower, a resistor might not work in terms of current the winding can provide and it might be better to use a separate heater transformer.

If the Rigonda heater is also 11-12V, an extra capacitor might be needed to tame the line output stage a bit.
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Old 4th Feb 2024, 5:44 am   #8
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Default Re: Fun with a Rigonda VT100m

I was given one of those Rigonda VL100M's back in the 80's, complete with A3? sheet shematc, that had an intermittent picture.
I took it to a TV repair shop, but they couldn't find the fault / said it was BER?
But, whilst stripping it down, I annoyingly discovered there was a broken joint on the EHT cable (buried inside a block of wax around the EHT rectifier diodes).
I can't recall what happened to all the parts inc. the boards & the CRT - I fairly sure the case was thrown-out, but I night have kept the handle / aerial etc.
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Old 4th Feb 2024, 10:48 am   #9
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Default Re: Fun with a Rigonda VT100m

Sorry to hear about the o/c tube heater. The Philips T-Vette is also prone to this.

A long shot but it may be possible to weld the heater back together if its mostly intact ie a minute gap. Have a look at this thread https://www.vintage-radio.net/forum/...php?t=49752but but be very careful if you try the suggested methods due to the dangerous high voltages involved.

Another set, preferably one with a valve line output stage would be probably needed so that a higher EHT is available to provide a decent enough arc to form the weld.

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Old 4th Feb 2024, 1:57 pm   #10
G8vsjDave
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Default Re: Fun with a Rigonda VT100m

That was a good idea Symon, I used an ignition coil left over from my wife’s old Renault Megane and pulsed it from a 555 and a high voltage transistor. Unfortunaly, it didn’t manage to repair the CRT heater, but it gave a good arc.
Dave
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Old 4th Feb 2024, 2:05 pm   #11
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Default Re: Fun with a Rigonda VT100m

Not sure about EHT, but i have successfully welded an open cathode on a GEC 9 inch tube, and open heaters on a CRM123 using the anode from a line output valve (adjusting line frequency does make a difference to the weld), specifically a 6P28 or PL38 in an Ekco television. To attempt heater repair one side to line output anode on supply set, the other to chassis.
Would suggest initialy just tapping the connection to the valve to see if the heater break is small/close, if it does nothing then tapping the neck of the CRT may be necessary to vibrate the ends closer.
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Old 4th Feb 2024, 2:24 pm   #12
Philips210
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Default Re: Fun with a Rigonda VT100m

Stephen's right about the EHT. It works better from the RF pulsed high voltage typically taken from the top cap (anode) of a line output valve. Gently tapping the neck of the tube is a good point too. The thing is you have to quickly disconnect the HV feed once it welds for it not to immediately fail again.

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Old 4th Feb 2024, 4:02 pm   #13
slidertogrid
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Default Re: Fun with a Rigonda VT100m

Welding an OC heater where the connection at one end where the heater attaches to the lead out wire and is almost touching is feasible. But where a heater has been blown open by overrunning and it is the actual heater that has failed open is a different matter I'm sorry to say.
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Old 11th Feb 2024, 3:32 pm   #14
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Default Re: Fun with a Rigonda VT100m

Sorry to hear this Dave, but just to think outside the box, you could look for one of the Chinese tubes and scan coils of @ that size, I guess they would be much more plentiful.

It would at least allow you to move the project forward until the real deal turns up. E Bay used to be full of 'kits' for sets using them so there should be a few around even if you can't find one in an old TV.

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Old 11th Feb 2024, 3:53 pm   #15
G8vsjDave
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Default Re: Fun with a Rigonda VT100m

Yes, I'm keeping all my options open for now and the new Line scan circuit seems to working well. Thanks for your help.
Dave
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Old 11th Feb 2024, 7:08 pm   #16
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Default Re: Fun with a Rigonda VT100m

Quote:
Originally Posted by Maarten View Post
What's the correct voltage for the Rigonda?
According to a Russian data sheet for 6 inch 70° tube, the heater voltage is nominally 1.35V, minimum 1.2V maximum 1.5V. Heater current is quoted as 300mA ±30.

Nominal EHT 9kV, minimum 7kV, maximum 11kV.

Rich
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Old 12th Feb 2024, 8:18 pm   #17
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Default Re: Fun with a Rigonda VT100m

Oh wow, that's probably less than 1 turn even on the old transformer, hence the resistor.
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