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Saga of a Philips K12 Chassis..still ongoing!  

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Red_to_Black
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Yes, I just looked at the version in the library and it is the same Pdf I have, as you say from the same source 😀 

"This is my multimeter. There are many others like it, but this one is mine. My multimeter is my best friend. It is my life. I must master it as I must master my life. Without me, my multimeter is useless. Without my multimeter, I am useless."

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Posted : 19/02/2020 7:17 pm
Red_to_Black
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If its any Help I have a rather grotty manual of the K11 which uses the same grid drive arrangement as the K12 but without the Hybrids, this uses conventional transistors instead, the grids are simply fed with R-Y,G-Y and B-Y signals respectively, the Hybrids in the K12 must be just non-inverting High voltage buffer amps as they are fed with the same signals at their Base connection.

Actually looking again at the K12i manual, the circuit diagram for module U410 is actually shown and with component values, the (somewhat cryptic) block diagram part is only for the actual IC, maybe a better datasheet for the TDA 2771 IC would throw some light on things, the three output Hybrids as already said are probably just straight buffer amps.

"This is my multimeter. There are many others like it, but this one is mine. My multimeter is my best friend. It is my life. I must master it as I must master my life. Without me, my multimeter is useless. Without my multimeter, I am useless."

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Posted : 19/02/2020 7:43 pm
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Jayceebee
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That circuit helps tremendously, it should be very possible to check the film resistor values even without removing stuff. Only R1127 would be difficult due to it's high value but I wouldn't suspect it for no red. "Intergrund stabilis" the block via pin15 in the feedback path from the RGB modules would seem to equate to Background stabilisation or auto greysacle I would think.

John.

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Posted : 19/02/2020 9:10 pm
Red_to_Black
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I also meant to point out that in typical Philips style that IC 1101/U410 is shown in two parts (for those not familiar with Philips diagrams) the second part shows the contrast and colour control bits, it is on the same page but at the bottom left, annotated as 4B and part IC 1101 (b), that is what the "torn page look" is for on the parts of the module and IC.

Apologies if this is teaching granny etc..

"This is my multimeter. There are many others like it, but this one is mine. My multimeter is my best friend. It is my life. I must master it as I must master my life. Without me, my multimeter is useless. Without my multimeter, I am useless."

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Posted : 19/02/2020 9:22 pm
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crustytv
(@crustytv)
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I wasn't aware of all that which is what led me to think It wasn't of much use, thanks for the insight 👍 Guess I've been spoilt with the simplicity of Thorn circuits as well.

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Posted : 19/02/2020 9:30 pm
Jayceebee
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Oh yes, interpreting Philips and Sony manuals is a skill in itself. GR1 chassis, line stage startup via the volume control with an electrolytic from the main HT for instance? 🤣 

John.

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Posted : 19/02/2020 9:54 pm
Red_to_Black
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Another thing that might help the OP is that the output Hybrids are interchangeable as well, so are easily swapped with another gun to rule them in or out.

Thomson and B&O diagrams are just as cryptic in their own peculiar ways, one of the joys of being an independent repair outfit was we had to quickly get to grips with many different makes and their various styles of documentation 😜 , Thorn definitely had the best manuals by far 👍 

"This is my multimeter. There are many others like it, but this one is mine. My multimeter is my best friend. It is my life. I must master it as I must master my life. Without me, my multimeter is useless. Without my multimeter, I am useless."

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Posted : 19/02/2020 10:20 pm
PaulGoggo1
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@red_to_black

Hello , yes I had already swapped over the thick film units but no change. Scope checks confirmed no red output from the Martix module.

So trying to get either a module or TDA2771 IC to confirm.

Thanks Paul

 

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Posted : 20/02/2020 3:24 pm
PaulGoggo1
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Hello

I think I may have found a source for a TDA2771. watch this space. In the meantime here is a scan of the Colour output section in my Philips K12i. its the 30ax version.

This diagram was found in a brown envelope inside the set!

Philips K12i 30AX RGB section

Paul

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Posted : 20/02/2020 9:36 pm
Red_to_Black
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That diagram looks at first glances the same as the one Chris and I have.

This set seems to use colour difference drive to the grids of the Crt as opposed to RGB drive to the cathodes which most later CRT sets used, this means the that the final matrixing is done in the tube itself and that the Y or luminance signal is supplied to the cathodes commoned out.

This technique is a bit before my time so I am not fully conversant with it but was routinely done with valve and hybrid sets, Thorn being an exception of course which used RGB drive from the get go.

The only late-ish model that I can recall that used this technique was a mid 90's Matsui portable which I must admit stumped me for a while until the penny dropped.

Have you tried cleaning the printed spark gaps yet ?

The TDA 2771 chip is not one I am familiar with either but some of these chips do shut down their outputs if expected input/output/feedback signals do not fall within expected parameters (see Chris's Telefunken Aphelion story).

Whilst this chip certainly pre-dates full auto-greyscale (TDA3562) it will most likely have had some black level stabilisation feedback loops incorporated so these are worth going over very carefully, Jayceebee mentioned earlier too.

"This is my multimeter. There are many others like it, but this one is mine. My multimeter is my best friend. It is my life. I must master it as I must master my life. Without me, my multimeter is useless. Without my multimeter, I am useless."

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Posted : 20/02/2020 10:23 pm
PaulGoggo1
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My K12 now has its Red output back!. It was the TDA2771 IC. This is mounted on the matrix module, a bit tricky to change but doable.

Picture looks good. (CRT is excellent) The moire pattern on the screen shots are due to the camera. the picture is clean otherwise.

3 problems remain. There seems to be am elusive dry joint/ connection somewhere around the tuning/control panel or the main chassis area (see pic). it was damaged by a previous leaking NiCad memory battery which leaked onto the pcb, rotting  a few tracks. If you flex the board the set will go into a dead/standby type mode, but then there is no display. Very elusive so far to trace this.

In addition it has a strange frame sync fault. the picture will suddenly loose frame lock, running very fast. no amount of frame hold tweaking will stop it. only by interrupting the signal or channel change will sometimes stop it.

Line sync seems ok. odd one this.. Frame pulses look clean going into the sync module.

Otherwise it works fine (except for the speaker which hasn't been repaired as yet)(problem 3!)

I have attached some pictures of the set working with its newly restored red!

Paul

Philips goya 965 K12 chassis 2
Philips goya 965 K12 chassis Tuning Panel
Philips goya 965 2
Philips goya 965 K12 chassis 3
Philips goya 965 1
Philips goya 965 K12 chassis 1

Mod Note: Merged this new thread with the old. Better to keep it all as one thread rather than two, It makes more sense as it has all the previous work and diagnosis that lead to this point.

 

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Posted : 09/03/2020 7:25 am
PaulGoggo1
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Thanks Mods. will do this in future.

Paul

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Posted : 09/03/2020 12:12 pm
colourmaster
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Hi Paul, it's funny that you should mention the intermittent shut down fault. My has a similar fault where it suddenly shuts down with no channel display then comes straight back on. Once it's warmed up it shuts down all the time, I'd be interested to know what it is that's causing it. 

Regards. Gary. 

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Posted : 09/03/2020 10:06 pm
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