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Vintage Television and Video Vintage television and video equipment, programmes, VCRs etc.

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Old 28th Dec 2006, 9:10 pm   #1
marcus 3500
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Default Jvc 7440

Hi all

For the last few years this set has been sat in a corner in my siste'rs old bedroom at my Mums.

Today I powered it up: the fault with it is there is very weak sound and no picture but if you slightly off tune it there is a faint picture and the sound is gone.

I've never seen any fault reports in Television Magazine - I have all issues from 1966 to 2005, but I do remember seeing a picture of the JVC 7440 with the back removed on the front cover of a 197? TV mag, but with no mention of the TV inside.

Do any members here have any service info, or may have repaired these sets and know this fault?
If so I would be very glad to hear from them

The TV is dated the 17th week 1973 inside. With it being from the colour boom of 1973 and the first(?) JVC colour set for the UK I would love to see it working in tip-top condition again.

Regards

Marcus.....
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Old 28th Dec 2006, 9:26 pm   #2
Steve_P
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Default Re: Jvc 7440

Now this is one I haven't seen (!) but we can make a start without a manual. Are there any voltages printed on the IF or tuner units? Sometimes there are, and they are helpful in this situation.

When it's not on a station, do you get white noise on picture and sound? If this is there and OK, then the tuner is suspect. If this is weak or non-existent, go for the I.F. Board. Very much like a BRC 1400/1500 chassis.

Hope this helps!

Cheers,

Steve P
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Old 28th Dec 2006, 11:59 pm   #3
marcus 3500
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Default Re: Jvc 7440

Cheers Steve for the super quick reply

There are no voltage markings on any of the PCBs, sadly

When it's not on a station, there is no white noise on picture and sound, so the fault must be on the IF board and not the tuner.

It can pick up all 5 stations' sound very poorly, but no picture.
Will post more info on Friday THANKS for the HELP and INFO Steve Cheers for pointing me in the direction of the IF section - duff transistor maybe?

Regards

Marcus....
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Old 30th Dec 2006, 12:09 pm   #4
marcus 3500
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Default Re: Jvc 7440

Hi all

On Friday I took the JVC in to the workshop, and after removing the back spotted a tagstrip at the back of the tuner.

There were 2 leaking caps (50V 47UF and 50V 3.3UF). After fitting 2 nice new caps I decided to remove a sealed can that's screwed on the side of the mechanical tuner. It's a 2 transistor IF amp board - none of the transistors inside were faulty but there were a few ringed dry joints.

After bolting the tuner back in, it was time to power up.
Sadly, only a slight improvement, and the contrast control does not work.

After a coffee I decided to take Steve's advice and have a look at the IF and AGC boards on the IF board.
There is a test point TP93; 15V when checked it was only 11.4V. After going around the cable runs, I found the 15V comes from a small PCB in the centre of the TV called the AUX power unit. There are only a few caps, resistors and 2 diodes but one cap stood out the most; 50V 470UF was bulging and after removal both legs were corroded.

New cap fitted; time to power up again and check the 15V supply; now its only 11.7V and the picture is still the same.

Time for more coffee and a think.... decided to remove the IF board and check transistors.
The very first transistor I checked was X51 TYPE A564; dead short all pins.
The rest of the transistors are fine on the IF board. After having a quick look for my transistor equivalents book I did not find it and it was time to come home.

I'm off now to the workshop; if I dont find my book would someone please let me know the equivalent for the A564.....

Regards

Marcus......
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Old 30th Dec 2006, 12:15 pm   #5
Kat Manton
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Default Re: Jvc 7440

Hi Marcus,

My Towers says 2SA564 = BC212L

(The "2S" is missed off the package, "2" = 2 junctions, "S" = Silicon.)

Regards, Kat
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Old 31st Dec 2006, 10:10 pm   #6
marcus 3500
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Default Re: Jvc 7440

Hi all

After leaving the workshop to warm up for an hour i started to look at my small draws of Transistors ive had these for well over 20 years after removing them from smashed tv's i found dumped on country road edge bottoms and the edge of the local woods when i was about 12 years old, i never found a complete TV the back had always been kicked off and a brick would be lying were the scan coils once were

In the second draw hidden under an old speaker sticker was a 2SA546 the very Transistor i needed it would seem to have been worth getting scratched and cut hands and arms all those years ago

With the 2SA564 fitted it was time to power up again and with a few tweaks on the convergence i was watching BIG starring Tom Hanks the only thing left to sort out was the faulty contrast but that turned out to be easy the contast control is connected to a switch at the front called day time, night time and just needed a squirt of switch cleaner

Im pleased with the results the TV was left on for over 5 hours and no other faults have shown up so its time i sneaked it back into my sisters old bedroom so i can start work on the next set a PYE CT200

THANK YOU Steve, Danny and Kat for your kind help.

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; 17th Oct 2007 at 12:13 pm. Reason: Readability
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