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Old 7th Apr 2020, 7:47 pm   #1
ekjdm14
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Default TX100 B chassis repairs...

Hi all, been a while since I found time or motivation to get online but with our current situation I've found myself slowly going through the round tuit pile. On the chopping block today is a C. 1987 Logik (Dixons?) 4298 colour set.

This is using a Thorn chassis, TX100B driving a 56cm 701 CRT. Remote control, no text, RF input only. The set was working when I bought it a year or so back, although the alignment seemed off (could tune for either good picture or good sound not both, if I brought sound in then I'd lose chroma).

So, pulled the back off today & removed the chassis for cleaning and inspection (because lockdown...) and boy, judging from the lacklustre repair work, am I surprised it worked at all! For a start the HOT is floating with it's heatsink from one leg, with 2 dry joints onto damaged traces and the LOPT has been out in the past too, signified by 2 broken traces repaired with telephone wire. A few other transistors also show signs of being removed in the past.

Anyway, glad I found this before it blew up & will rectify the sloppy soldering and bodge repairs before I continue. What I wanted to ask though, is if anyone happens to have a PDF of the schematic they'd be happy to share since it's obviously not in the VRSD database being a TV.

Also, I believe the alignment issue is likely due to the Golden Screwdriver (given the state of the rest of the work I've seen) but aside from Mr. Twiddler, is there anything else that could have caused the sound & picture to have drifted apart?

Many thanks, Dan.
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Old 7th Apr 2020, 9:02 pm   #2
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Default Re: TX100 B chassis repairs...

PM sent, RE:manual.
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Old 7th Apr 2020, 11:56 pm   #3
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Default Re: TX100 B chassis repairs...

Thanks, reply sent

Spent a while reworking the previous repairs in a manner I felt more acceptable (actual whetted solder joints included!) and main chassis should be ready to go back in tomorrow, then diagnosis can start on the alignment knowing it's not likely to fry semiconductors if I bump the chassis this time.
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Old 8th Apr 2020, 9:58 pm   #4
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Default Re: TX100 B chassis repairs...

Up and running, what a disappointment the CRT is in this. Appears to have either run with no line scan or possibly been used with a CCTV unit with 2 cameras vertically split as there's a visible line running down the centre of the tube when running. Also needs a darn good degaussing since it's got a nasty spot next to the speaker, presumably down to having stood inactive for so long (or maybe the previous "tech" removed the speaker screws and let it rest against the CRT.

That aside though, it's actually not working too bad considering it's RF only, sound is much better now & have confirmed my rework is correct thanks to the schematic from Baz (The diode mod. board is slightly different to the Thorn ones, but close enough that I could verify a repair to it's traces). Much appreciated, should come in handy in future if the CRT comes back a bit better with running/degaussing as It'll possibly end up restored then seeing as I think it's quite an oddity for it to have survived thus far. (previous shocking repairs were done sometime after 1996 from the date on the LOP transistor, so guess they can't have been all that awful!)
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Old 8th Apr 2020, 10:34 pm   #5
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Default Re: TX100 B chassis repairs...

Hi.

The purity fault maybe due to the degaussing positor crumbling.

Is that the A56 701X Videocolor S4 CRT? They were great when new, giving a nice sharp display but I remember having a fair bit of trouble with those tubes in ITT sets (CRT made by SEL). You used to get an odd focus problem at higher beam current, the raster pulsated with a pinging sound in the tube but cleared as the brightness control setting was reduced.

I personally preferred the 30AX CRT in the TX100 which was longer lived (apart from early batches).

Regards,
Symon

Last edited by Philips210; 8th Apr 2020 at 10:43 pm.
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Old 8th Apr 2020, 10:56 pm   #6
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Default Re: TX100 B chassis repairs...

Yes, having cold started it a few times with no change I have to agree it's unlikely the degauss is doing anything. It is an A56 701X CRT, not sure of manufacturer but think it was made in France if that means anything? The display is certainly good and sharp although the A1 pot is super-touchy/dirty & don't really fancy spraying it, it's plenty good for now anyway & only issue noted aside from the purity is the possible burn-in.

Will attend to the degaussing first off though, as that's the main problem. Thanks for the input, will add some pics when it's looking better in case anyone's interested.
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Old 8th Apr 2020, 11:28 pm   #7
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Default Re: TX100 B chassis repairs...

Always interested Dan and we like pics, lots of pics
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Old 9th Apr 2020, 1:17 pm   #8
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Default Re: TX100 B chassis repairs...

OK now a question, how does one decode the part number of the degauss positor? the current (pun not intended?) item is a 96009 and the closest i can find quickly is a 96209, I presume this denotes either a difference in current handling or a variation in temperature coefficient of one/both of the thermistors? (From what I glean, a positor is pretty much a PTC and an NTC tied together, one to slowly reduce current through the coil & the other to act as a shunt across the coil.)
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Old 9th Apr 2020, 2:13 pm   #9
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Default Re: TX100 B chassis repairs...

Just a thought. The sound may be set up for 5.5mc/s for the Continent. ? John.
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Old 11th Apr 2020, 4:33 pm   #10
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Default Re: TX100 B chassis repairs...

These Logik sets were built down to a price, and the obvious way savings could be made was by specifying a cheap CRT. We had several go within a year or two. They were 'white label' - no manufacturer, made in France.
The round white 9009 posistor is common and can be replaced with the 9209. The only one that won't work is the similar looking 9012 which Philips alone used to confuse us all.
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Old 11th Apr 2020, 4:54 pm   #11
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Default Re: TX100 B chassis repairs...

Haha brilliant, Philips are great... Yes I was rather thinking the CRT might be a bit on the weak side also, it's a little washed out but not been able to get a test pattern on it as yet (lost the remote for the DVD player I was using). Very apparent they're a cheapie set when you look & feel the materials used so wouldn't surprise me.

Might also be the reason for the sloppy '90s repair work on the line stage, customer said throw it as too expensive to repair, so they pass the set to the apprentice and let him have at trying to fix it for himself while getting some practical experience?

Is there any reason the sound would be set up "Continental"? Surely Logik would only have been sold in the UK being a Dixons house brand?

Thanks all,
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Old 11th Apr 2020, 5:18 pm   #12
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Default Re: TX100 B chassis repairs...

It's only a thought. Used abroad maybe. I think the TX100 uses crystal filters in the sound channel. They should be 6mc/s. Worth a check. It might save some head scratching.
I've never had a TX9//10/100 twiddled. Good luck with it. John.
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Old 11th Apr 2020, 5:21 pm   #13
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Default Re: TX100 B chassis repairs...

Quote:
Originally Posted by Welsh Anorak View Post
[snip].... The only one that won't work is the similar looking 9012 which Philips alone used to confuse us all.
Am I right in thinking that's a fairly broad spectrum of what's acceptable then, and something like a 98009 would also work?

I have a source of a 96209 but the pin spacing is slightly different, which i can work with, but there's also a 98009 available a little cheaper (only £3.50 Vs £5.00 but every little helps not get crucified by SWMBO haha).
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Old 12th Apr 2020, 12:35 pm   #14
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Default Re: TX100 B chassis repairs...

Yes - that'll work. I used to have a big drawer full when i ordered 50 rather than 5 by mistake - mind you I don't think I've any left now!
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Old 12th Apr 2020, 7:29 pm   #15
ekjdm14
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Default Re: TX100 B chassis repairs...

Quote:
Originally Posted by Heatercathodeshort View Post
It's only a thought. Used abroad maybe. I think the TX100 uses crystal filters in the sound channel. They should be 6mc/s. Worth a check. It might save some head scratching.
I've never had a TX9//10/100 twiddled. Good luck with it. John.
Ceramic filter in sound I think, will have a look see what it says but the set came with a UK plug that looks to have been on for many years by the screws (not that it means much I know).

Certainly worth a check, it has some strange behaviour to be fair. Feeding a signal through a SCART/RF modulator, if I tune it in on ch1 it's near impossible to get decent & the tune changes significantly when the AFC defeat is released (tune for good pic/buzzy sound & close the door = loss of sync & white noise).

Channel 16 is largely similar, big change between AFC or no. Channel 9 though has little variation whether AFC is defeated or not, and has the best sound of the three although the picture is noticably darker and has less contrast. Will spend a while tuning in other channels too but any clues as to why this might be? Perhaps Ch9 was a VCR channel originally?

Will also try it out with a VCR connected instead of the modulator in case there's something about that the set doesn't like.
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