Removing a Fluorescent Display

[Charles]

My stereo receiver (a Sony STR-AV780) has a vacuum fluorescent display (VFD)
which goes dim intermittently. I have replaced some electrolytic capacitors
already which has helped but there is another one I'd like change.
Unfortunately it is mounted UNDER the VFD. The display tube is about 7 by 2
inches and mounted in a dual-inline socket. The socket is not a
zero-insertion-force model.

How do I remove and replace the glass display tube without damaging it?

Chuck

 

[[email protected]]

I have worked on many Sony receivers with Fluorescent displays..... I
am guessing that what you are thinking is a socket is really a spacer
and the display is soldered directly to the pcb. .... simple enough,
get your solder wick out and un-solder and remove the display.
electricitym

 

[Charles]

I have worked on many Sony receivers with Fluorescent displays..... I
am guessing that what you are thinking is a socket is really a spacer
and the display is soldered directly to the pcb. ....

Oooooh, I'll bet you're right.

simple enough, get your solder wick out and un-solder and remove the display.

I had considered doing that. It wouldn't take me too long and there's a much
lower probability of damaging the display even if that spacer was a socket.

Thanks for the reply.

 

[James Sweet]

Oooooh, I'll bet you're right.
display.

I had considered doing that. It wouldn't take me too long and there's a much
lower probability of damaging the display even if that spacer was a socket.

Yeah give that a shot, those Radio Shack desoldering irons work pretty well
for that sort of thing, one of the few worthwhile things they sell. Also if
it has pins on both sides you may find that desoldering one side is
sufficient to flip the display up and get to that cap.

 

[Dave Moore]

yup, I was going to say 'if in doubt just unsolder
the socket'



: : > I have worked on many Sony receivers with Fluorescent displays..... I
: > am guessing that what you are thinking is a socket is really a spacer
: > and the display is soldered directly to the pcb. ....
:
: Oooooh, I'll bet you're right.
:
: > simple enough, get your solder wick out and un-solder and remove the display.
:
: I had considered doing that. It wouldn't take me too long and there's a much
: lower probability of damaging the display even if that spacer was a socket.
:
: Thanks for the reply.
:
: --
: Chuck
:
:

 

[Charles]

Yeah give that a shot, those Radio Shack desoldering irons work pretty well

for that sort of thing, one of the few worthwhile things they sell.

I've got my trusty Edsyn Silverstat Soldapullt at hand. It works well if I keep
it clean and greased. (About twenty years ago the nice people at Clearco
Products sent me a 2 ounce sample of their silicone grease. I love that stuff.)

Also if it has pins on both sides you may find that desoldering one side is

sufficient to flip the display up and get to that cap.

Those pins look pretty stout and I think I need to heat up the pins anyway.

I took the cover off the receiver this morning to monitor some voltages. As
luck would have it, the display, which was dim when the cover was on, is fine
now.

This is beginning to smell like a cold solder joint. I had the same problem
with a Sony TV a while back. Heavy components vibrate slightly while going over
the solder bath on the conveyor. They keep vibrating while the solder cools.
As I resoldered the connections to the flyback transformer of that TV receiver,
one of the joints gave an audible crack as I relieved the tension on it. After
that it quit eating the horizontal drive transistor.

Maybe the fluorescent display has the same problem.

 

[Charles]

I spent about two hours this afternoon removing the fluorescent display and
replacing the electrolytic capacitor hidden underneath. electricitym was right.
The display (a Futaba 1-519-392-11) was not socketed. It is soldered directly to
the printed circuit board and held off the board by a plastic spacer.

There are about 80 connections to unsolder which didn't take long. The only
hangup was releasing the spacer from the board. One of the three tabs which
secures the spacer to the board was tight. I inspected and straightened all the
pins on the display before reinserting it so lining the pins up to reinsert the
display went well.

The display which was exhibiting some uneven illumination yesterday looks good.

 

[[email protected]]

I spent about two hours this afternoon removing the fluorescent display and
replacing the electrolytic capacitor hidden underneath. electricitym was right.
The display (a Futaba 1-519-392-11) was not socketed. It is soldered directly to
the printed circuit board and held off the board by a plastic spacer.
There are about 80 connections to unsolder which didn't take long. The only
hangup was releasing the spacer from the board. One of the three tabs which
secures the spacer to the board was tight. I inspected and straightened all the
pins on the display before reinserting it so lining the pins up to reinsert the
display went well.

Probably an Elna capacitor? Sony has a tendency to use those leaky s*ns
of b*tches...

 

[Charles]

Probably an Elna capacitor?

It was a Nichicon.

I have found a some failing electrolytics in this 18-year old unit but most have
been okay. I still haven't found the cause of the dim display. The brightness
was fine for a few hours but now it's back to uneven dimness. The power supplies
are right where they should be so I'll have to go deeper and measure some
voltages on the display board.

 

[Charles]

For people reading this thread in the archives, here's what I found as the cause
of the dim display on my Sony STR-AV780 receiver. (This probably also applies
to the STR-AV790 and STR-AV880 receivers.)

All the DC voltages on the fluorescent display appeared normal. Then I checked
the AC voltage across pins 2 and 75 of the display while it was dim. It was 3.1
volts. The correct value is not marked on the schematic so I waited until the
display was at full brightness. Now the voltmeter read 4.6 volts! I was able
to correct the dim display by tugging on the cable attached to connector CNJ33
at the main board. Then I found that a little push on the 1.5 ohm resistor R818
which is in series with the power supply circuit to the display also brought
back full brightness.

I resoldered all the connections in the area of the resistor. It seems to have
fixed the problem. I'll watch it for a few days before I put the cover back on.