Thorn CT512T has expired.

[sentinel040]

I bought this ex-rental TV somewhere back in the mists of time; I have lost track of exactly when, but it was at least 25 years ago. As I no longer watch TV here I removed the tuner some years ago and it has continued to give good service hooked up to a DVD player via a SCART lead, although the remote control no longer works. Anyway, it continued to soldier on until the other day. Part way through a DVD there was a noticable "tick", that's not a good sign thinks I. Then some tens of minutes later another, this went for about a hour when there was a final "tick" and off went the picture and sound. Oh dear thinks I; is it time to "invest" (that is probably not the right word) in a replacement, or do I try to sort this one out?

When you plug it in and turn it on it goes into standby with the red LED lit but the moment you bring it out of standby the LED extinguishes. Having pulled it to bits, there is nothng obvious, well hope springs eternal!

Now, this is probably a bit like the famous "how long is a piece of string" question but, any ideas anyone? I do not have a manual/circus diagram, which is a bit of hinderance, and as regards TV knowledge, I used to be a Saturday lad tarting up 850's, 950's etc many years ago and as part of a past day job I used to have to sort out monitors (and just about anything else electronic we had to fix).

I will appologise in advance but I sometimes have to go away for days at a time at short notice so if a response seems tardy, that will be the reason.

Anyway, many thanks in advance. Ian

[1955APREN]

Hi Ian
the ticking that you heard was likely arcking off the eht part of the set. as the set is now dead the arcking as damage the line output transistor or the line
output transformer. Have you got any test equipent a meter. if so with the set unpluged from the mains connect the black lead from the meter to chassis and the red lead to the collector of the line output transisitor . with the meter set on the ohms range tell us what the reading is. I think that is set uses the icc2 or icc5
chassis not not liked by lots of service eng"s and compared with the tx100 & tx 90,s. It would help if you could send a photo or the chassis.
Kind regards Derrick

[Nickthedentist]

What chassis is this then?

[sentinel040]

Good afternoon. I have plenty of test gear here; sorry I should have said! Having delved back in and has a closer look I noticed what appeared to be a spike of solder originating (that was its thickest end) from the Emitter pad reaching across the gap in the PCB and touching on the Collector pad. It's unlikely to have all been there since it was built so i find it interesting. Anyway, removing it has resumed normal service. I have included (hopefully) images of the chassis and the area of interest; if the forum software has resized it correctly (I had put my camera back to its normal settings after tthe chassis pics before I spotted this and forgot to select a lo-res setting again - ).

Anyway, thanks chaps, if I had waited until I obtained a "comic" and not started to dig around I would not have fund that so quickly.

For the record, I would like to know what the chassis actually is and where I could get a "comic", ready for next time. I have also learnt yet again (for the n th time....) to stop looking for the complex problem!

[HamishBoxer]

Possibly ICK2? If it is indeed Thorn.

[steve1010uk]

Could this be a Daewoo CP330 in disguise ?

[FERNSEH]

In the last days of DER when it became DER Direct the Thorn owned company was renting out cheap TVs sourced from the Far East. I'm sure the rental company was using the Thorn brand and not DER. Definitely not a Thomson set.

DFWB.

[canonman75]

Originally Posted by steve1010uk

Could this be a Daewoo CP330 in disguise ?

On the second photo it does say CP330 along the right-hand edge of the board.

[sentinel040]

It's pretty obvious that it is a bit of badge engineering, the electronics are all of far eastern origin. I cannot even remember who I bought it of for certain but whoever they were they had a place in Lichfield. In all fairness it's not too badly put together. So it remains a mystery; lets hope I never need a manual!

[paulsherwin]

The solder blob looks as if it's been there since the factory and has taken all this time to go bad. Presumably some arcing caused the edge of the blob to melt and bridge the gap permanently.

[HamishBoxer]

Looks like the dust across the gap made it it happen.

[jayceebee]

Originally Posted by canonman75

On the second photo it does say CP330 along the right-hand edge of the board.

The CT512T and it's sister the NICAM CT514TN were indeed Daewoo based, at this time around the mid 90s Thorn badged anything from anyone. There were even rebranded Philips models, very surprising to me as you have to remember that Philips and Thorn had been major rivals.

Apart from the usual rental outlets there was also a retail operation called Fona (formerly Rumbellows). This tried to go upmarket even selling entry level B&O products but charging a premium for the rebranded stuff some of which was very poor quality Chinese rubbish, the buying public caught on and Fona failed. I believe the B&O franchise was quickly withdrawn when they found their products being sold at a discount, a heinous crime. I must be the only trained Beotech to have never repaired a B&O product, the training courses were excellent and had mountains of manuals delivered to my home address each month. Wish I still had them.

Back to the CT512T, the LOPTs were a weak spot arcing to the core causing lots of damage. Also I think there were two 780x regulator ICs, a 7805 and 7809 possibly. The 7809 was the most problematic.

John.

P.S. Any Beotechs on here? How do you dismantle a Beotime?

[julie_m]

I guess this could be another manifestation of the "AF11x disease" that affects many 1960s transistor sets, where fine "whiskers" of tin grow from the inside of the transistor can and short against the electrode structure.

[sentinel040]

Sorry for the delay; my thoughts were along the me lines as Julie's, having seen wiskers on the outside ot ACxxx series transistors. With regards to arcing causing it, I have to admit to being a tad dubious as I heard less than half a dozen flash overs before it became a permanent fault. Although I stand to be corrected.

Thanks again.

Ian