CTV 1976/1977 Sharp C-2051H - Linytron

Next connected the set to my signals rack feeding in test cards, tried tuning in on BBC1, nothing, the control was turning, but it felt like it was at the end of travel, it wasn't. Tried BBC2, same thing, tried ITV and this time I could see it was tuning, then in came a frame rolling test card, of reduced height.

So, with the test card on screen I adjusted V-hold and got it locked, I thought about taking a photo at this point but decided to figure out the location of the height control to expand the test card, when all of a sudden there was a god almighty bang and a plume of dust C514 on the vertical PCB exploded.

All the caps in this TV are either Nichicon or Nippon Chemi-con and, despite their legendary status, are just past their prime. I'm done with trusting them, they're almost 50-years old, so for once I'm abandoning my usual practice of fix on fail and will be replacing what remains.

With regard to the tuner, I'm going to have to remove the PCB, as all the tuning sliders are either failing or failed, as to the reason why, i've no idea yet.

Tuner PCB drying out in the sun after PCB cleaner applied. Once dry, I'll squirt the tuner pots with switch cleaner.

Yes, even lower voltage capacitors can suffer from depletion of the aliminiumn oxide insulating layer, what you could have done is power the low voltage rails from a bench power supply first before switching on but a good result so far Chris. 

An excellent result Chris, I don't think those physically leaking capacitors would have reformed no matter how patient you were!  I had one go bang like that years ago, it whistled past my ear !  

Never in the field of TV resurrection has crusty replaced so many, when normally my objective is to see how few it takes. I took my time and was as methodical as I could be in replacing these ageing electrolytics. Let's see what havoc I have or have not unleashed, fingers crossed no man made errors.

It was also an opportunity to thoroughly clean all the PCB's with Amberclens

Reassembly and power will take place after some lunch. One thing for sure, considering the state it had been stored in prior to coming into my possession, it'll now be either the cleanest working or non-working chassis.

Beats working on a DVB-T2 modulator in front of me that keeps rebooting - which seems to be either a low 12V rail, a high 24V rail... or worse.

All back together, now for the moment of truth.

Spoiler

Did I mess up?

No, I didn't Phew!

Now I need to have a look at the manual, and follow the set-up procedure. I've not looked yet and assume there is one in there. I've done nothing to it thus far, this is what I have.

Looking good Chris, That's a hell of a faulty parts Bhaji ! 😀  

An excellent result, that will be quite a rare set now, all you need in the period video to go with it. 

That’s looking good now Chris!

Another one saved! 

I'm following the 12 point plan for gray scale tracking and black level. I get to point 7 connecting the scope to J1 (J1 was not illustrated on the diagram, so yeah, they make you hunt that down) and then adjust (P.L.S) R444 to get the black level aligned with the pulse of the wave form.

Can anyone, who has downloaded (in vrat tech lib, but I've attached the section) the manual, help me understand point 7. I have the pulse wave form but cannot understand when adjusting R444 what I should be seeing. The figure of waveform 'A' shows the pulse waveform and a dotted line. Am I to assume the dotted line is zero and the wave form should sit above? If so, how imprecise is that!

Either I'm incredibly dumb (which I fully accept is likely) or Sharp are totally crap at creating easy to follow technical data and cct diagrams

The 18" version setup for point 7, makes far more sense.

It begs the question, "why a different procedure for the 20?"

I am sorry Chris I can't help with the interpretation of the instructions, but a lot of early Japanese instructions were often poor translations. How it wasn't picked up by the importers and corrected is beyond me, maybe it was too late by then or they just didn't bother. There was some real howlers ISTR. "Open chinflap point at AFC and twist" springs to mind... 

 I often found sets needed tweaking by eye despite service manual instructions. The set up procedure on the 3500 for instance. you could set it up 'by the book' but sometimes it still needed a tweak on either the A1 pots or one of the drives in the end...

Edit: maybe the 18" instructions were later where the information had been clarified? I can't see the screen size making any difference to the procedure.

Posted by: @slidertogrid

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Edit: maybe the 18" instructions were later where the information had been clarified? I can't see the screen size making any difference to the procedure.

Without studying the two respective diagrams, I think the circuits of the C-1851 and C-2051 must be significantly different. I only have 7.1VDC on J1 with very little variance from that when adjusting left/right. The 1851 expects around 135VDC, this must explain why point 7 is different.

Just ignored step 7 and followed everything else, my logic being the phantom twiddler will have played with the RGB bias and drives, but perhaps not been aware of the black level pot, which is not easy to find.

I now have a massive improvement in picture quality now. The screen pot, RGB bias pots and RGB drive pots, had all been significantly twiddled from optimum, in fact they were wildly out. I'm very pleased with the final picture.

Time to put the back on and move on to another set, thanks for all the interest, input and encouragement. 👍 

That looks good Chris! It begs the question with the tube being so good why did someone twiddle it?  The amount of 3500s I bought that had been written off for the tube being low when the set had not been set up correctly was incredible! 8500s as well, flaring madly ! it always made me wonder when we got a VCR in that had been twiddled! Why? I remember someone bringing in a radio for repair "I have tightened all the screws..."  He meant the I.F transformers of course! 😬 

Posted by: @slidertogrid

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It begs the question with the tube being so good why did someone twiddle it?

Maybe component drift (most of my bhaji bucket were out of spec) impacting performance, coupled with idleness or lack of time to do component level fault analysis, so take the easy option, compensate with a quick twiddle, of course that supposition could be twaddle. Another possibility is someone didn't have access to a service manual to follow the Gray-scale set up and just winged it.

Yes I suppose so. It is easy to be critical of previous repairers and sometime justifiably so, but I remember being a young field engineer with 15 jobs a day to do,  corners were inevitably cut a little. You were expected to repair most in the home.  So yes, the odd 47K was tacked on the back of the line board. Sometimes a control would be at the end of it's travel but if the picture was OK you were out the door!

I remember covering one of the older engineer's service area when he was on holiday, I did the repair and the customer commented " You soon fixed that" " I think the other bloke is getting too old, he had to get his maps out last time".  (I wanted to be out of there ASAP, it was one of those houses where you needed breathing apparatus!)

When a set was eventually returned to workshop for say a new tube the field 'repairs' were rectified, but not always...

Posted by: @slidertogrid

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"Open chinflap point at AFC and twist" springs to mind... 

Ah, Jinglish. Some of the translations for professional video equipment were similar: "try falling over and press reset" was my personal favourite - from the NEC 'E-Flex' DVE manual. See also: "shift resistors" (should be 'registers') and "lutches" ('latches').

I have no idea as to the veracity of this statement (and I find it doubtful, even a bit offensive myself), but it was said to me many years ago that the reason for some of the poor translations was that it was considered a loss of honour to involve foreigners to provide a foreign-language translation.

@cathovisor I have seen safety warnings that include "Nice Electric shock" or how about a "Religion free DVD player" ? I bought a can of Cat Frezer recently. All I need now is a Cat that needs frezing... 😉