HMV 2634 12 inch mains portable Thorn 980

[unitelex]

I like this 980 set. I had one as a student in the early 80s. Think it was the HMV one.

I converted the time base and sync sep to 625 line (just a few cap changes) and added a video buffer and used it as a monochrome monitor for my Sinclair Spectrum which had a video out mod. Remarkable easy to do. With isolation transformer of course!

Best Regards
Chris

[Richard_FM]

Originally Posted by unitelex

I like this 980 set. I had one as a student in the early 80s. Think it was the HMV one.

I converted the time base and sync sep to 625 line (just a few cap changes) and added a video buffer and used it as a monochrome monitor for my Sinclair Spectrum which had a video out mod. Remarkable easy to do. With isolation transformer of course!

Best Regards
Chris

That's interesting to know, the Spectrum didn't have a sound output through the RF so you didn't need to worry about patching that into the 980.

[Focus Diode]

Originally Posted by clockman

Update on my Thorn 980 6641 12 inch portable
I have fitted the new PL81 and checked the heater chain continuity now 1.5 k including the W10 heater rectifier i have had a good look round it has had some repair work done on the PCB so i must have bought it second hand or part/ex but it was working when i put it in the loft . i have given it a bit of a spring clean there nothing missing or damaged . i will not be plugging it in as my days as a TV repair man are now in the distant past .and i do not think spares are available so i will put it back on the shelf for now . PS i have just done a perfect restore job on a Philips B23G25U a great little set TAB

Some spares can be interchanged with parts from other sets. I know a Thorn 1400 sound output transformer will work and the frame tx is the same as that used for the Thorn 950. It's unlikely the line output transformer will be defective.

I'd be tempted to run it with a Variac if cold checks are ok!

[clockman]

Thanks for your encouragement but looking at the sets PCB all in a tiny space plus all that high voltage i do not think i am able to tackle that task i do have the original service manual but i do not think TV repairs are for me at my time of life. As i am a EX/TV engineer now aged 84? so i think i will stick to my simple vintage radios and old clocks. TAB

[Tazman1966]

Hello Clockman.

I'm just up the road from you in St Albans and have repaired/restored a few of these Thorn 980 portables. In fact, I have a couple of them as well as a smashed Ultra Cub. If you fancy having it got going, I'd happily tackle it for you just for the price of any components. Let me know what you think.

All the best from Tas.

[clockman]

Yes, i would be happy for you to have a look at it and would be happy to pay any costs i will give you my email address for you to contact me [Removed] hope to hear from you soon. TAB

[Tazman1966]

As already explained, Thomas lives down the road from me in Borehamwood so during his shopping trip to St Albans on Friday, he dropped it off at my house and left promising to return when the Covid restrictions are eased in a couple of weeks.

He explained that he'd carried out a couple of repairs in the past including some damage to the PCB and that it had been in use as a kitchen set for many years on its internal telescopic aerial on channel 1 (BBC1) and channel 9 (Thames/London Weekend Television) and gave very good results.

The following day, I opened it up and sure enough, the PCB was in a poor state with cracks galore and many tracks bridged with wire links and a few very small ones simply bridged with solder. In general, very nicely done indeed.

As I don't like unexpected bangs, I replaced the mains filter cap and then powered it up via my lamp limiter and left it simmering for a good while. Nothing untoward happened and the HT smoothing can remained cold so I hit it with full mains. Very soon, sound burst forth but no line timebase activity was present. A quick check revealed that HT2, the HT line to the line timebase, was missing. R115 was dry jointed and the track had lifted. With this made good, we now had some action. A distorted test card, weak line sync, poor frame linearity, width that only just made it and low brightness. The sound was low too.

Some routine capacitor replacement - C25 sync separator grid coupling, C69 screed grid decoupling for the PL81, a very leaky scan coil coupling cap C64 sorted out the wonky sync and improved the width. Further improvements to the width happened after replacement of the high value resistors in the width/line stab circuit.

Next, time to tackle the egghead shaped frame linearity. Anyone who knows these sets is very aware of the nuisance of cap replacement in this part of the circuit as the capacitors are right under the CRT bowl so you have to dismantle the set to get to them. Part of this involves sliding the scan coils off the neck of the tube. Unfortunately, the line linearity sleeve fell to bits on doing this so I had to repair this too. With the caps replaced, the frame lin was sorted.A few more physically split Dubilier caps were replaced as were the two resistors in the video amplifier screen grid feed which were very burnt and miles out of tolerance.

The picture was now very nice and with a replacement PCF80 audio amp/output valve we were in business with improved sound. I reckon Thomas will be pleased with the result although I have one more fault to attend to which materialised on soak test. The line frequency twitches from time to time and it pretty "tap worthy". This will necessitate another dismantling session. I had this with my Marconi Mini version of this chassis and it turned out to be very poor contacts on the line oscillator valve base which I ended up replacing which cured it. Maybe it will be the case with this one too. I'll let you know.

[Heatercathodeshort]

Nice work Tas. These 980s always brush up well. Line twitch on any chassis can be frustrating but don't overlook the hold control itself. This chassis would probably cope with a 20" tube in a wood case. EHT a bit low but I bet it would work well.

Those frame caps are a pain to replace but you only have to do it once. Regards, John.

[Tazman1966]

Thanks John

This one, I think, has the same styling as yours. They are excellent little sets aren't they? The chassis drove the 16" 981 very nicely too so I reckon you'd be right about managing a 20" tube. I haven't measured the EHT on these, to be honest.

As far as replacing any of those components under the bowl of the CRT, it's made a teeny bit more annoying by having to unsolder the earth lead from the tube and unsolder the two leads to the speaker mounted audio output transformer. You would have thought that they would have been pluggable. Same with the scan coils. It would have been nice to leave them in situ on the neck and simply unplug them. Ah well, all part of the fun, I guess.

[beery]

Hi Tas,
I'm glad you were able to get this set going for Clockman.
BTW, the other day I watched a film called "Performance", I can't recommend it, it was awful after a promising start, however it did include a mauve one of these sets. I wonder what brand that was sold under?

Cheers
Andy

[Richard_FM]

Originally Posted by beery

Hi Tas,
I'm glad you were able to get this set going for Clockman.
BTW, the other day I watched a film called "Performance", I can't recommend it, it was awful after a promising start, however it did include a mauve one of these sets. I wonder what brand that was sold under?

Cheers
Andy

I think these were sold under all the brands Thorn were using at the time.

[Restoration73]

It's notable that the design of the square porcelain wirewound resistors was new. Later
versions with a slot in the body could incorporate a tag/support to aid heat dispersion
and also the sprung fusible type where the solder melted to offer circuit protection.

[dazzlevision]

Originally Posted by Restoration73

It's notable that the design of the square porcelain wirewound resistors was new. Later
versions with a slot in the body could incorporate a tag/support to aid heat dispersion
and also the sprung fusible type where the solder melted to offer circuit protection.

Yes, those in the photo were made by Dubilier (UK) - marked “DCC”. Later production (or spares provided by Thorn/BRC) were the stand-off type, usually made by VTM.

[Hybrid tellies]

That is looking really good Tas. Great write up as well.

[Tazman1966]

Originally Posted by beery

Hi Tas,
I'm glad you were able to get this set going for Clockman.
BTW, the other day I watched a film called "Performance", I can't recommend it, it was awful after a promising start, however it did include a mauve one of these sets. I wonder what brand that was sold under?

Cheers
Andy

Hello Andy.

I have the mauve/burgundy one myself. It's an Ultra "Cub" model number 6641. I did a write up on it way back in March 2009! Here's the link to the thread.

[Tazman1966]

Hello again and thanks for the replies.

Just a quick update. It was the valve holder that was faulty. After completely dismantling the set again, to gain access to the valve holder I replaced it with a nice new ceramic one and now the line hold is rock solid. I also checked the anode loads on the valve. One had already been replaced but the other was way up. Now the line hold is rock steady.

[clockman]

Hi love all the posts and the work of Tazman is "amazing" so would you believe i have just seen my famous Thorn 980 set on last nights TV episode of Public Eye on channel 81 .Talking Pictures TV i just new it had a famous past with TV appearances ? TAB

[Tazman1966]

Fame and fortune for your little 980

You tried phoning me the other day but I was driving my bus and couldn't answer. I tried phoning back a couple of times but no answer. I'm on lates this week but off next Tuesday and Wednesday if you want to come round and collect although on a further soak test another fault has shown up. A very occasional momentary frame collapse a couple of times when warming up which sorts itself out after a short time.

I've enjoyed getting this set going as I really like them. I'll have to look out for a 981 16" version using the same chassis - much rarer.

[toshiba tony]

Was this set equipped with capacitor fed heaters? I seem to remember the value of said cap was very critical, good sets though.

[Restoration73]

Only early 960 and 1580 chassis used capacitor dropper. The 1580 does have similarities
with this set, being the last 12" hybrid portable.