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1959 KB QV30/1

 
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1959 KB QV30/1

Post by AidanLunn » Sun Jun 05, 2016 1:33 am

Hello all

So after the nightmare that was the Invicta, I've decided to shelve that and start on this (far easier to service) KB QV30/1

Progress so far has been quite fast and I'm back to enjoying the restoration (when I read back on the Invicta thread, it sounds like someone who doesn't enjoy the hobby or job - well I didn't enjoy the Invicta at all!), however I've got myself stuck in a rut. I was going to finish this first and then post the results and restoration here, but events have conspired to force me to do this early.

At first the TV started up and cause the hum you see in picture 2. Soon afterwards the mains smoother can gave up by going short circuit and slowly spewing its innards out, so I replaced the can (a tube out job, although *FAR* easier than the Invicta!) and then I carried along my merry way finding and replacing faulty capacitors and resistors (although no valves have needed to be changed yet) and I now find myself at this juncture. Adjusting the brightness changes the shape of the raster to thinner and taller, reducing it makes the raster shorter and wider.

The one last problem is low HT, which seems to be the cause of a lack of height and width and also slight linearity problems (as the frame stage is being starved of HT). According to my Trader sheet for this model, assuming an input set to the 240-250VAC setting the HT should be a figure of 237V after the rectifier diode then 230V after smoothing and the choke. Boost HT should be 710V.

On this set the HT after smoothing measured 209V, boost measured 545V. My voltage selector was set to 220-230VAC, so I changed it to 240-250VAC and the HT reduced to 180V. I replaced the smoother with new large capacitors, suitably rated. These still test OK, although if these were faulty I'd usually have expected additional symptoms on screen and in speaker. Before I corrected the mains selector, the anode of the FC31 measured -24V, cathode 217V (and then 209V after smoothing).

So does it sound as though the metal HT rectifier diode type FC31 has been damaged by the behaviour of the original smoother can?

I will take it out and test it tomorrow, but what do other members think?

The pictures below give an idea as to the progress.
Attachments
KB1.jpg
KB2.jpg
KB3.jpg
KB4.jpg
KB5.jpg

 
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Re: 1959 KB QV30/1

Post by AidanLunn » Sun Jun 05, 2016 1:35 am

The last two pictures here represent the change in the shape of the raster depending on the brightness level.

I mist say I think this set is going to be a good performer as well. The Brimar C17AA CRT is excellent!
Attachments
KB6.jpg
KB7.jpg
KB8.jpg

 
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Re: 1959 KB QV30/1

Post by sideband » Sun Jun 05, 2016 9:03 am

Change the rectifier for a 1N4007 or something similar. You'll need a limiting resistor in the anode, about 25 ohms is a good start but be prepared to adjust the value up or down to get the HT right.

The original metal type (presumably selenium) will be well and truly faulty by now.

 
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Re: 1959 KB QV30/1

Post by Cathovisor » Sun Jun 05, 2016 11:24 am

I shall be following this with interest as I too have one of these sets: but unfortunately, a transformer is connected to the CRT on mine...

 
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Re: 1959 KB QV30/1

Post by AidanLunn » Tue Jun 07, 2016 6:45 am

I still haven't got round to testing the diode (which I also suspect is faulty after this time). I don't have any 1N4007s in stock, but loads of 1N5404s, would they do?

Cheers (and now I realise I didn't put I in the OP, thanks for any help offered).

 
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Re: 1959 KB QV30/1

Post by nuvistor » Tue Jun 07, 2016 7:30 am

use two 1N5404 diodes with a 220k balance resistor across each diode. The 5404 has a smaller vrrm amongst other parameters that are different.
Confirm the set has suitable fuses in case the diode goes s/c and a suitable surge limiter resistor say 22ohm 10 watt, whether you use 2x 1N5404's or single 1N4007.
Frank

 
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Re: 1959 KB QV30/1

Post by slidertogrid » Tue Jun 07, 2016 9:28 am

Hi, what a nice set! I have got some IN4006 s 800v 1A if they will do? If so PM me your address and I will send you a couple.
regards
Rich.

 
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Re: 1959 KB QV30/1

Post by crustytv » Tue Jun 07, 2016 10:46 am

Aidan,

Its worth stocking up on all the 1N4xxx diode range as you get hundreds for very little outlay you will always find you need them. That goes for all sorts of other diodes including Zeners, I spent a couple of years ordering odd and ends and more than I needed. Now I rarely if ever have to purchase diode stock and it didn't break the bank doing so.

Just to throw another suggestion in to the mix to compliment the other two. After advice from a time served TV engineer I stopped using 1N4007 1000V 1A diodes in that position, I now use the far beefier 1N5408 1000V 3A, these too can be had for pennies.

As you can see from the photo below a bit more robust than the 1N4007

diodes.jpg

 
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Re: 1959 KB QV30/1

Post by nuvistor » Tue Jun 07, 2016 12:12 pm

The 1N540x range also have less recovery transients, and will probably not require a capacitor across the diode as with 1N400x range

Frank
.

 
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Re: 1959 KB QV30/1

Post by Duke Nukem » Tue Jun 07, 2016 12:51 pm

I've been quite lucky so far (hmm ... this is gonna tempt fate!) but the few sets I've worked on with metal rectifiers have been OK, but if I did replace one I'd definitely do as Chris has suggested, go straight for a 5408. 60p from Maplin, <10p in quantity from other usual supplier.

TTFN,
Jon

 
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Re: 1959 KB QV30/1

Post by Refugee » Wed Jun 08, 2016 11:48 am

The cheapest way is to go for the UF range.
UF5408 will do service as a fly back diode in a solid state TV or even a VGA screen.
They have come down in price now that SMPSUs have become common.

 
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Re: 1959 KB QV30/1

Post by AidanLunn » Sun Jun 12, 2016 2:21 pm

An update:

Short version: Replacing the HT rectifier brought the HT up but made no difference to what was on screen. So by doing that I'd won the battle but not the war.

Longer version:

Since the last post I have replaced the HT rectifier (more on that in a second), but I first replaced C93 (0.05uF/350V wax/paper type) with a 0.047uF (473J) 630V polyprop type. This resulted in the raster being much compressed, as in the image below. The image below is of the raster as its maximum now.

I have checked my work around there and all seems OK, so I thought that if the HT and everything else was OK, then the presence of the old C93 might have meant the picture may have been much higher than it should have been.

After this the height pot did have an effect, but mot much, the total effect between max and min height was only about an increase/decrease in height by about an inch or two.

After this I replaced the HT rectifier with a 1N5408 (leaving the 15 Ohm surge limiter that checked out OK alone) and this made a huge difference to the HT, brought it up to about 210V, but still short by about 20-27V. So I inspected my work on the mains selector (remember, the mains selector knob had fallen to pieces, so I soldered in a link behind) and discovered I had set this to the wrong voltage. Resetting to 240/250VAC and cleaning the HT fuse and associated connector brought the HT up to a much more respectful 245V - a little higher than the service manual states, but surely not enough to matter?

But the effect on screen remained stubbornly the same. Not enough width and certainly not enough height, in fact no different at all to how it was before I had changed the HT rectifier and sorted out the mains selector.

So I fished around and found R108 (1M) had increased to 15M (tested by lifting one leg), and then found that it seemed to be acting as a thermistor, for about 2 minutes after the set was off, the resistance decreased back to about 1.7M. Solder back in and switch the set on for a few minutes, then switch off, desolder both ends this time and measured and it repeated the process.

So I replaced this with a 1.2M (all I had in stock) and this seems to be staying stable, but when checking around the height pot, I found that there is a dead short between both ends of the pot, whereas the maximum the wiper can get up to is about 300K. I began checking around the height pot because after I had replaced the R108, the height pot then had no effect at all on the circuit, the height remained fixed at what you see in the below image.

As it was getting late I forgot to take the boost HT voltage, but I guess if the height pot is short, that would be bringing down the boost HT, possibly resulting in a lack of width.
Attachments
KB9.jpg

 
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Re: 1959 KB QV30/1

Post by Duke Nukem » Sun Jun 12, 2016 2:37 pm

I dont think pots go s/c end-to-end so somethig else must be shorting it. Anyhow, have you definately replaced the boost cap?

TTFN,
Jon

 
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Re: 1959 KB QV30/1

Post by Cathovisor » Sun Jun 12, 2016 3:19 pm

Any chance of a peek at the relevant bit of circuit?

 
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Re: 1959 KB QV30/1

Post by crustytv » Sun Jun 12, 2016 3:31 pm

Snippet from Trader Sheet 1457

qv30.jpg

 
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Re: 1959 KB QV30/1

Post by Cathovisor » Sun Jun 12, 2016 3:32 pm

:thumb

 
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Re: 1959 KB QV30/1

Post by Cathovisor » Sun Jun 12, 2016 3:44 pm

Looking at that circuit, the only way you can make that pot look short end-to-end is for either (a) R95 to go s/c or (b) the end of C80 that isn't connected to HT has been shorted to ground.

 
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Re: 1959 KB QV30/1

Post by AidanLunn » Sun Jun 12, 2016 3:47 pm

Jon: yes I have replaced boost rectifier, also tried replacing the boost rectifier and LOP valves - no difference to the width.

EDIT2: I also remember adjusting the width sleeve. Again not a lot of difference.

Catho: I was just trying to scan in the Trader diagram but with my scanner settings in Windows Fax and Scan adjusted to minimal settings that anything could be made out and then compression through IrfanView to 250KB in a PNG file the results were extremely poor, so I just uploaded all 8 pages of the Trader (2 pages per scan) to 4 images on Photobucket at full quality. Not ideal but the best I can do.

EDIT: I notice that Chris has posted a scan of that part of the circuit but from another source, so I will still go ahead and link to scans of what I have been working with. I've come across situations where two different prints of the exact same circuit in two different publications have given different component numbers before, so I still think it's important to link to scans of what I've been working with.

Circuit diagram including frame stage: http://s1255.photobucket.com/user/Aidan ... y.jpg.html

Tuner circuit diagram and component layout: http://s1255.photobucket.com/user/Aidan ... q.jpg.html

Valve line up and supplementary info: http://s1255.photobucket.com/user/Aidan ... 0.jpg.html

Other supplementary info: http://s1255.photobucket.com/user/Aidan ... 7.jpg.html

Thank you very much for all the help.

Turning this problem on its head I'm now considering the possibility that the height and width problems are not related, but I'll check the TV again soon.

 
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Re: 1959 KB QV30/1

Post by freya » Sun Jun 12, 2016 9:25 pm

Hi Aidan,

Which service sheet are you referring to when Quoting C93?

Aidan Lunn wrote:Since the last post I have replaced the HT rectifier (more on that in a second), but I first replaced C93 (0.05uF/350V wax/paper type) with a 0.047uF (473J) 630V poly prop type. This resulted in the raster being much compressed, as in the image below. The image below is of the raster as its maximum now.



It seemed to get worse after C93 from your previous picture.
Last edited by Katie Bush on Mon Jun 13, 2016 2:52 pm, edited 1 time in total.
Reason: Repaired broken qoute.

 
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Re: 1959 KB QV30/1

Post by Refugee » Mon Jun 13, 2016 12:59 am

The photo has not stuck to the thread. It will need to be added.

 
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Re: 1959 KB QV30/1

Post by AidanLunn » Mon Jun 13, 2016 7:54 am

Hello Freya

I've been using the Trader sheet I linked to all along.

I have found that R115 was shorted to chassis by the outer shell of the resistor partially disintegrating and making contact with a chassis tag. That has restored control over the height but not the height itself.

The boost line still remains stubborn at 590V instead of 710V.

Many thanks,
Aidan

 
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Re: 1959 KB QV30/1

Post by freya » Mon Jun 13, 2016 8:20 am

What voltage do you have on pin 7 of V13, don't test the anode on pin 6 it may upset your meter due to the high peak voltage here.

 
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Re: 1959 KB QV30/1

Post by slidertogrid » Mon Jun 13, 2016 9:58 am

I have had a changed value focus pot dragging the boost line down on sets in the past, you could try disconnecting the supply to the "hot end" of the focus pot to see if it has any effect on the boost line?
Rich.

 
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Re: 1959 KB QV30/1

Post by Katie Bush » Mon Jun 13, 2016 3:17 pm

There would seem to be some "talking at crossed purposes" here....

Jon asked.....
Duke Nukem wrote:I dont think pots go s/c end-to-end so somethig else must be shorting it. Anyhow, have you definately replaced the boost cap?

TTFN,
Jon


Aidan replied.....
AidanLunn wrote:Jon: yes I have replaced boost rectifier, also tried replacing the boost rectifier and LOP valves - no difference to the width.



Which still leaves the question, has the boost capacitor been changed? - If not, and if leaky, it will bring down the boost and HT voltages.

Just trying to be be clear if this step has actually been carried out. :)

Marion

 
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Re: 1959 KB QV30/1

Post by AidanLunn » Mon Jun 13, 2016 11:45 pm

Katie Bush wrote:Which still leaves the question, has the boost capacitor been changed? - If not, and if leaky, it will bring down the boost and HT voltages.

Just trying to be be clear if this step has actually been carried out. :)

Marion


Oh dear, another "Aidan mistake". Yes I have replaced the boost capacitor (and both LOP valve and boost rectifier). Although the only other PY83 boost rectifier I have is used so there *could* still be scope for a fault if that one is low emission (I don't have a valve tester nor any other TV that uses a PY83), so I've ordered a pair of new PY83s.

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