KB QV40 Fringe Version - Request for advice.

[DoctorWho]

Dave - That's very helpful, thank you. We had no way of tracing where that lead went, hopefully that may help improve things.

David - Thanks for explaining, it does seem somewhat complex. We don't have the correct circuit to work from, so I'm afraid that re-drawing the circuit is probably beyond my abilities.

Do the two screen shots above give any indication as to what may be wrong? I'll post more later on when we have the brown lead back in the correct place again.

Thanks for the help.

Peter.

[DoctorWho]

Originally Posted by Dave Moll

According to my book, pin 6 (pentode anode) of V10 (PCF80 - synch sep & afc) connects to R130 (82K) and C57 (0.1uF - in video amp/vert synch amp). I hope that helps.

We've just tried to locate this, but because we don't have the circuit diagram, it's a bit like trying to locate it in the dark.

Can you tell me if this connectes to a valve base directly, or via a resistor, not not at all? If it does, then which valve?

Any other indications would be very much appreciated.

Thanks again.

Peter.

[channel405]

I have been working on this set with Pete and just to add my findings: it seems that the line stage is not operating properly. The line whistle sounds a bit shrill, when the line hold is advanced there appears to be a brighter section of raster coming in from the sides to the centre as the control is turned up (higher line frequency). Also when we are able to get some form of picture of Test Card C we can't get any sync lock (line or frame) but there is at least two circles of the test card on the screen moving into or away from each other as the line frequency drifts. This makes me wonder if there is line foldover of some kind? We tried to capture this with the first off screen photo Pete posted last night but it is difficult to capture without fast shutter speed so it just looks like the line hold is out on the photo.

The audio is distored with vision on sound so there seems to be at least two faults, poor reception/response of tuner/IF section and sync seperator/line timebase section as well as the mysterious wire from pin 6 of the PCF80 on the PCB that goes nowhere. Could this wire be the cause of the strange line symptoms? We are doing this blind as we have no circuit diagram. Thanks Dave for shedding some light on this but we need to know what R130/C57 is connected to (valve etc) so we can identify them. We tried connectingthe wire to pin 2 of the ECC82 but it didn't like it! Any advice appreciated- thanks!

[Steve_P]

Here's the circuit. Hope it helps. What exactly are your problems now?

Cheers,

Steve P

[Steve_P]

Right - Pin 6 of the PCL80 is the Anode of the Pentode Section. It goes to R130 and also to C57, which hangs off the Anode Section of V5, which is the Video Amp and Vertical Sync Amp. C57 hangs off R56, which goes to R57 and then to the Grid of the Triode Section. V5 is a PCL84.

The tuner/IF problem - replace the valves in the tuner. If this does not help, take it apart, clean and check. Check C34 and also make sure the valve resistors are OK.

Cheers,

Steve P

[DoctorWho]

Thanks guys, that's excellent. Tim has now gone home, so I'm sure he'll pick up this data and take it from there. Hopefuly the set will soon be up and running, it certainly looks like it will display a first class picture when it's running properly.

[Sam]

Originally Posted by DoctorWho

Does anyone have the correct data for the QV40 please?

I have a lot of KB TV Service Books back in Norfolk. I will be there at the weekend and check through them, if it isn't too late by then!

Sam

[Heatercathodeshort]

Hello again Peter,
It looks like you have solved the lack of sound and vision signals on your QV40 but as I have taken the pictures of the 'Fireball' tuner I thought it might as well be posted as these tuners were fitted to a huge range of models and may be of interest to others.
A rotted I.F. output coil lead will cause no signals with very little if any reaction when the tuner is rotated. Voltage to the mixer anode, pin 6 of the PCF80 will be very low if not absent. The coil wire goes through a yellow sleeving and its the wire in this sleeving that goes o/c. The repair is easy but you need a steady hand!
Another cause of lack of signals is o/c of the HT feed resistors to the oscillator section, the 6.8k and 4.7k one watt resistors that can be seen at the front of the picture.
The Fireball tuner was made under licence by A.B. metals in this country. It was an original design by Standard Coil Products of the USA.
It is a very good tuner and only requires an occasional clean of its silver plated contacts on the 'Catherine Wheel' coil assembly.
The PCL85 was not available until 1961 and I'm sure the PCL82 is the correct replacement. Regards John.

[DoctorWho]

Thanks John, they are very helpful pictures, I am sure they will be helpful to Tim. Thanks for the detailed explanation as well, it's very nice to understand the issues related to this more deeply.

Tim still has problems with the set as you can see from the posts and acsrrn shots above, we hit a brick wall with these.

[Heatercathodeshort]

Just a quick thought Peter, make sure you have the correct valve in the horizontal oscillator position V11. It should be an ECC82 [12AU7] An ECC81 [12AT7] or ECC83 [12AX7] may have been fitted by mistake in the past especially as you had the PCL85 in the frame position. Welcome to the world of 'Flywheel Sync'! This circuit is slightly out of regular procedure for the times and the resistor count is high. It will be necessary to check these with care and the valve voltages. Do not 'blanket replace' components. You will end up with a minefeld! This is not going to be as easy as the 702..
Regards John.

[DoctorWho]

Thanks John, this isn't actually my set, it belongs to my firnd Tim (Channel405), he was staying with us and we worked on the set together. It's very modern compared to the sets I am used to.

Thanks for the advice, I will pass this on to Tim.

[channel405]

Just wanted to say a quick thanks to all the contributors above and Steve P for the data etc. When I have gathered some courage and have a bit of quality time for me and my KB, I'll have another go.

So watch this space..........!

[DoctorWho]

Thanks to David (Fernseh) for a much clearer circuit diagram, posted here with his permission.

[channel405]

Right I have now at long last decided it's high time to have another crack at this set. Mainly because our 42" Sony LCD colour thing in the living room is no longer with us, and I though it would be nice to have a 17" black and white 405 set in it's place! So I need to get it going quick before the Mrs plugs the gap with another modern horror!

Thanks all who helped before. I now know where the loose wire is supposed to go. From pin 6 of V10 to R130 and C57 to the anode of V5. But what is the value of R130 so I can identify it please? And which pin of V5 is C57 connected to. Thanks Steve P for the diagrams, but unfortunately the res is a bit too small to resolve the text/numbers etc. Thanks too to David (Fernseh) for his diagram, but the connection I need to know about now goes to the frame sync pulse clipper, I need to know where it goes please!

Thanks

[Steve_P]

What have you got on this sat at the moment? Sound, IF and RF ok? Line frequency right?

Take some pics so we know where we're starting from with this.

Cheers,

Steve P

[channel405]

Thanks Steve,

Right, sound OK bit crackly but put that down to speaker/vol pot. There is video reaching the tube but no syncs of any kind especialy line. I will take a photo of this but it's is difficult to describe in the meantime.

The line whistle sounds a bit rough, the nearest I can get to line lock/correct line frequency the pick still looks like the raster is folding over horizontaly on it's self so there is multiple thin images with no lock. I wondered if this was to do with the linerity sleeve thing on the tube neck as this was all a bit rough. I have since took that all apart but it made no difference.

What I have deduced so far is the lead that comes from Pin 6 of V10 goes nowhere as C57 and R56 are missing. I am I right R57 is the 330K connected to pin 1 of V5?

Standby and I will take pics of the raster/line symptoms asap.

Cheers

[channel405]

Here are a few off srceen photos of a testcard.

The 1st shows the symptom with the line hold control about halfway. The second with the control advanced to about max and the 3rd pic is a close up of the edge of the raster showing the effect of the raster having what seems to be two edges to it. When the line frequency is increased the inner "raster" comes in from the edges of the screen towards the centre. The effect is lost a bit with the digi camera exposure timing.

So there seems to be two faults:

1. Lack of sync to V5 because there is no sync feded from V10. I need to know the values of C57, R56 & R57 and confirmation they connect to pin 1 of V5.

2. The strange line fault. Could this be a line output fault, connections on LOPT/scan coils/linerity sleeve etc?

[Tazman1966]

Hello.

As Steve always says a picture speaks a thousand words!

The other clue is that the line whistle sounds a bit rough. It certainly looks to me like the line oscillator is way off frequency.

Sorry I haven't got a diagram.

The odd fold over effect can often occur with line output stages of sets being asked to operate at frequencies miles away from where they should be.

Good luck and hope that helps,

[Steve_P]

The line frequency is defined by the Line Oscillator Stage, which is V11. This should be a 12AU7, or more commonly ECC82. Change this valve and look round here - something is amiss. If it's not a 12AU7/ECC82, this could well be your problem.

The line hold control is R145 (500k). Check this and C103 (500pf), R146 (820k), C102 (420pf) and R147 (10k).

Pin 1 of V5 goes first to R57 (330k) and the other end of that goes to a junction of R56 (100k), also C58 and R58 to deck and R59 to the HT.

This other side of R56 goes to C57 (.01, 150v) to pin 6 of V10 (PCF80).

Cheers,

Steve P