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Old 29th Jan 2007, 10:30 pm   #1
marcus 3500
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Post Sony KV1320MKII Low brightness.

Hi all

This past 2 weeks I've been trying to sort out what I should keep and which sets can go.
Need the space for some more sets arriving in the next week or so.

The problem with this little Sony is the brightness, contrast are set at full, but the picture is dark for the first 20 minutes the focus is poor and colours like red bleed to the right, with the brightness control up full.
Tube tired with age? Or is this a known fault with these old Sonys?
Any help will be much appreciated

Regards

Marcus.....
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Old 30th Jan 2007, 8:01 am   #2
slidertogrid
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Default Re: Sony KV1320MKII tube ?

Hi, You may find you can improve the picture by overrunning the tube heaters a bit. It may shorten the time it takes for the picture to improve at least.

If you identify the heater connections and run them from an ext transformer, you can see how much boost it needs before modifying the heater supply in the set.

Does the set have a resistor in series with the heaters? If so you could try lowering its value or shorting it out; it has worked for me on other makes.
best of luck! Richard.
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Old 30th Jan 2007, 9:32 pm   #3
marcus 3500
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Post Re: Sony KV1320MKII tube ?

Hi

Cheers, guys, for all the advice

Today I decided to take the little Sony apart all the cabinet (wood surround) not just the black back, needs to be removed.
The plastic back is screwed to the cabinet from the inside.

With the back now on the floor had a good luck around the chassis. Nothing too obvious was standing out (leaking, bulging caps, dry joints etc).
The tube heaters are fed from a very small transformer on the PSU with only a fuse in series with the heaters; no resistor, so after a coffee and a longer look at the chassis I decided to replace C608 33UF 160V, C522 33UF 160V, C512 10UF 150V, C516 10UF 160V, but there is a leaking cap on the tube base 0.47UF 500V. I've not replaced it - don't have this cap.

Switched the set on and a nice bright picture appeared and after setting up the H-STAT and the V-size, H-size, H-cent controls for the best picture on test card F the problem now is very poor focus BUT if the contrast is turned right down the focus is perfect when you turn the contrast up the picture balloons up with poor focus but the centre of the picture is in focus i cant find a focus control is the tube KAPUT and is there no focus control i dont have the service manual for this set if any members here have the service manual could you PLEASE tell me if there is a focus control or not

Regards

Marcus.......
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A rather amusing side effect is that all of our real hair fell out in the first 48 hours. PD500

Last edited by Mike Phelan; 3rd Nov 2007 at 11:10 am. Reason: s&p
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Old 31st Jan 2007, 1:54 am   #4
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Default Re: Sony KV1320MKII tube ?

Hello,

If I remember correctly, the first generation Trinitrons used a vacuum tube EHT rectifier, the only other "hollow-state" device along with the CRT. Maybe your rectifier can't keep up with the current demand and the picture "blooms", i.e. defocuses as brightness goes up.

Please check for the presence of this tube and eventually replace it.

Good luck with bringing this nice TV back to life,

Best Regards

J.halphen
Paris/France
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Old 31st Jan 2007, 7:30 am   #5
dsergeant
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Default Re: Sony KV1320MKII tube ?

KV1320s up to serial no 100,000 did in fact use a 3AT2 valve EHT rectifier. Later ones (presumably yours since you say Mk2) used a normal tripler LOPTX. I have never ever seen one of these earlier sets myself and wasn't aware of it till I looked at the manuals.

Dave
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Old 1st Feb 2007, 10:34 pm   #6
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Default Re: Sony KV1320MKII tube ?

Righto - well I've had the Newnes Book out and there is a KV1310 / KV1330 entry. So, assuming that this also covers KV1320 series, let's see if this works.

The focus volts, which are about 220v, are on pin 2 of the tube. It goes through R708 to a flylead, which is connected to pins F1, F2 or F3, to create the best Focus.

F1 is earth - I don't think so.
F2 links to R705 and R707 to deck, and there's a cap, C702, across R707.
F3 links to R705 and R707 to deck, and there's a cap, C702, across R707 and through VR701 as well.

The wiper of VR701 goes to R704 and then to g2 on pin 5 of the tube base.

If all of that makes sense, and even if it doesn't, there's a circuit attached.

Cheers,

Steve P
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Old 2nd Feb 2007, 9:49 pm   #7
marcus 3500
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Post Re: Sony KV1320MKII tube ?

Hi All

Thanks to Steve P for posting the Sony circuit of the tube base it now all makes sense the focus connections etc

With the meter now checking the resistors, three of them had gone up in value.

1 R704 100k, now it's turned into a 135K Resistor

2 R705 390k, now it's turned into a 574K Resistor

3 R708 470k, now it's turned into a 652K Resistor

Three new resistors later, the picture is now a lot better with regards to the focus but the workshop was quite cold this dinner time, and it took about 5 mins for full brightness to appear so the tube is probably worn.
The picture is fantastic compared to before the caps and resistors were replaced.

1 R704 100k, 2 R705 390k, 3 R708 470k, 4 C608 33UF 160V, 5 C522 33UF 160V, 6 C512 10UF 150V, 7 C516 10UF 160V

Thank you to ALL who helped with the little Sony CHEERS

Marcus.......
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