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.....

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

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....

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......

Re: Jvc 7440
 

Hi Marcus,

My Towers says 2SA564 = BC212L

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

Regards, Kat

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 :thumbsup: Steve, Danny and Kat for your kind help.

Regards

Marcus......