Can anyone offer a second eye, I'm looking at the feed into the contrast control, and it shows a ref of B2 for in and A104 for out to F1 (U405). Believe me, I've looked for hours trying to find B2, The modules are labelled on the cct as such, U405 (F1), U440 (F3), U548 (B3), U590 (B1) etc.
Ah, it's not just me then... my thought was that there must be a drawing for the customer controls somewhere?
EDIT: found it. Page 25 of the manual, section B of the circuits. Top right-hand quadrant, you will see a feed labelled A2 going to the contrast pot.
There you go... it's as expected, a variable DC potential.
If ever a service manual needed a backing of the pages with black card before scanning, this is it.
Sincere apologies for not reading @Crustytv's first post properly which states the CRT is a 20AX type, I've been looking at the K12/i manual which does use the 30AX CRT 😳Â
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I’ve been trying to make sense of that manual too, but I’m hitting a brick wall!! I suddenly thought maybe the B2 reference is to what is on page 10, where it shows the main board with a grid over it, A-F along the top, and 1-4 down the side.. but then where does A104 come into it?!
I can see why you are having trouble with this manual Chris! Even the iPhone 4 circuit diagram was easier to follow than this…Â
Map of U405 & U410 Plenty appears wrong there, but how where and why is another matter. I also checked all the supplies on U535, they are all spot on.
Edit: A1's all around 574V (measured with an old Fluke 75)
Don't forget some of those voltages will have been measured with something less sophisticated than that Star Trek Communicator 😉 of yours, so that could be an issue...
As for manuals, Brian Desmond (@sideband did I remember that name correctly?) who used to come around on technical training courses to our locale took a lot of flack on the manuals. He did promise us that Philips were aware of criticism and promised they get better but they didn’t improve that much.
No thats not me....Brian Desmond was one of our trainers
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Ah sorry! Brian Desmond was one of our trainers so yes you did get the name right. Haven't heard from him since we all got kicked out. I think he stayed on as an advisor to Funai when they took over making Philips brand TV's...like making sure they were made to Philips standard. No idea what he is doing now....
Michael Dranfield has been in touch (thanks Michael) and suggested the following:
1) I have a look at transistors TS617 & TS618, that they appear to be arranged as a latching device like a thyristor and would appear to reduce the contrast in the event of excessive beam current, the arrangement suggests a power down and pause would reset the latch.
2) Other than that, as beam current is also sensed at the earth end of the LOPT Michael also said to check the components here and also resolder the LOPT.
I removed the following:-
TS617 (BF423) Tested out of cct OK
TS618 (BC548) Tested out of cct OK
Tested the following in cct:-
R622 680R fusible 1/4W Tested 694R
R617 470R fusible 1/4W Tested 476R
That pretty much confirms what @marconi_mpt4Â stated, that he felt they were probably working OK.
As for item two, this has me, flummoxed, so I've asked where the beam current sensing components from the LOPT are as I cannot fathom it. If anyone else can shed some light on what components Michael is referring to, I would be most grateful.
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Chris, do you do watsap, I have found the K12 service manual.Â
Hi Michael, sorry I don't have any social media, other than Youtube.
If you go to the technical library at this forum, scroll down and there is an upload option.
https://www.radios-tv.co.uk/technical-data-library/
p.s.
Is the K12 manual in English?
No problem, I only asked as I can send pictures and video on watsap, so according to the service data that pair of transistors you have been looking at is a protection circuit for the CRT but it doesn't say if it reduces the contrast or switches the picture off, it does say in the fault flinging chart for contrast check those two transistors and a resistor R613 which seems to be the video output ht feed, beam limiting in this set is pin 7 of the LOPT and I would check the resistor and cap connected to this pin, also there is a connection to the CRT, prob aguadag, make sure nothings fallen off here.Â
I have the service manual if you want to borrow it?Â
Yes it's English, I also the the K12 projection service manuals
also there is a connection to the CRT, prob aguadag, make sure nothings fallen off here.Â
Now that's interesting, when I got the set indoors I heard something tinkle when the set was upended to get into the museum. I was careful so nothing was jarred. When I got it on the bench, I looked inside to see what that noise had been. I noticed this (see below) in the bottom of the cabinet. I thought ah aquadag spring has detached from the strap, but when I checked the strap was taught and still had its spring. I could not for the life of me figure what it was for, and assumed it must be foreign to the set.
Still no idea where or what it came from, but in light of what you mention above is it significant or a red herring?
Anything in your manual about a spring of that size? It's roughly 4cm in length and 5mm wide. It's rusted, split and lost its hook at one end.
![20230922 111457[1]](https://www.radios-tv.co.uk/wp-content/uploads/wpforo/attachments/884/15439-202309221114571.jpg "20230922 111457[1]")
Any chance you can scan the manual when you have spare time? That's hens teeth
EDIT:
I reckon that spring is a red herring, it's the remnants of an old one, the new is in its place, and you can see the rust where the old had been.
Here is the connection from the CRT PCB to aquadag
If you take a look at your diagram it's showing 2 connections to the aquadag,??Â
And there is a warning that says see service manual remarks.Â
While I can't remember the K12 because it's such a long time ago now I have found a service manual with one of my hand written notes on it, so I must have repaired these sets in times gone by.!Â
