i need help with a display issues with a old tuner

[dacflyer]

model FT-J2 HATACHI
my old tuner, the display is fading on it. i am thinking a resistor might be going bad, i hae not dug into it yet, but i'd like to get your opinion 1st.

here is the schematic... link is under the picture of the manual, small file
http://elektrotanya.com/hitachi_ft-j2_h ... nload.html

tuner looks like this..
http://www.hifiengine.com/manual_librar ... t-j2.shtml

i am guessing R535 560 ohm or R503 1K may be the culprit..

any thoughts before i dig in ?

[Janitor Tzap]

I may not even be those resistors.

Check the S6 (MW) and S7 (LW) switches.

Wiggle them up and down and watch the display.

If the display gets brighter even for a second, then try spraying some contact cleaner in them.

Dirty switches can give you a lot of headaches.


Signed: Janitor Tzap

[dacflyer]

tried that,,no change..you can see the display, but extremely dim..

[sghioto]

dac,

Did you check the 7.8 volts on the frequency counter chip? According to the data sheet the display module is a common cathode type with pin #1 connected to ground. The drive voltage is from that chip.

Steve G

[dacflyer]

nope, have not dug into it yet. was trying to get tips before i did dig into it.

[dacflyer]

i think i discovered the problem,, i am getting almost 14V to the chip and PS, and it should be 9V
the chip is hot as a firecracker, so i am sure it is toast,,it is a wonder that the other components are not cooked.,
not sure if i will find the chip to replace it...

[Janitor Tzap]

Ouch!

I looked at the +B 19V & +B 8V lines.

They are coming from the Power Supply/Amplifier board,
which is completely separate from the Tuner.

I'd check the +B voltages coming out of the Power Supply/Amplifier board.
The upc14308H IC801 8Vdc Regulator, and Filter Cap's may have gone bad.

I'd make sure these Voltages were alright first.
Before you start hunting for your display driver chip LC7257 IC502.


Signed: Janitor Tzap

[dyarker]

Agree with Janitor. Above you said display was dim, so chip is still working at some level. Get the supply voltage fixed and there is a chance it still works.

[dacflyer]

there is no amp with this unit,, i bought it at a flea market..someone had put a wall wart on it..
the display is so dim it is almost unreadable in the dark...even with the voltage reduced..
i even froze the chip and nothing..so i got the voltage right, i just need to hunt down the chip now.
if i can...

[Janitor Tzap]

{Slaps forehead!}

Dacflyer,
You should of known better!

That Walwart isn't going to be putting out a stable enough voltage,
like the one that the ORIGINAL Power Supply did.

I bet that cheap Walwart doesn't have any real filtering!
What is it?
An old computer power supply for a commodore 64 that was modified?
Or maybe a TI-99 computer power supply?

In any case......
I'd pull it apart and check it completely.


Signed: Janitor Tzap

[dacflyer]

i did not put the wall wart on it.. i measured the power coming out of it.. it was reading about 13.7VDC
was decent filtered, and the tuner worked, so i just assumed that all was well.. then about 6 months later ( on 24/7 ) then the display was suddenly dim, and never came back.

it has a proper regulated power supply now.. even 8VDC
trying to see if i can locate another chip.. if not, i'll just live with out it..
it still has the analog tune dial

[Janitor Tzap]

I found a supplier of your SANYO LC7257.

Quest Components:
http://www.questcomp.com/QuestDetails.a ... ck=YesOnly

They have 13 pieces in stock.
But you'll have to contact them for a price.


Signed: Janitor Tzap

[dacflyer]

thanx, i'll look into it.

[dacflyer]

finally found the chip i needed for my display, $6.12 from Ali-Express ( from china of course )
should be here in a few weeks as always with anything from there.

[dacflyer]

well China has screwed me again...
i had ordered the LC7257 and they sent me a LA7257, i tried to explain to them, but they replied with horrible broken english.
they did finally give me a full refund.. but it sux that they think they can snowball you.. i tried to explain to them i'd rather have the part i ordered, but they did not understand of course..

here is what they sent me... ----> http://s1129.photobucket.com/user/dacfl ... p.jpg.html Uggggggh!