Panasonic AG-1980 chroma noise/power supply buz

[Joe]

Hello,


I am embarking on a archiving task where I will be taking a library
of old home movies
on VHS and converting them to DVDs. The AG-1980 was heavily
recommended for
this task and I am in the process of getting it ready for some heavy
duty usage.


The unit I have will play tapes but it has the following issues:
1. When the power supply is loaded during playback or record there
is a relatively load static buzz sound coming from the power supply.
It is barely loader than the motor itself when the unit is openned but
I have never heard a normal VCR power supply this loud. It sounds
like the transformer is the one buzzing. I have replaced all of the
electrolytics in the PS unit and the buzzing got a bit quiter but is
still there. I checked all of the outputs and they look clean on the
scope.


2. I get chroma noise in the form of diagonal color bands over the
entire frame of video when in playback. If I switch the color/BW
switch to BW there is no noise in the picture. I am suspecting
something in the luna/chroma analog board. I have heard that
people generally replace caps in this area as well when they
refurbish a unit. Can the caps do this or is it something else?


I have the service manual and am slowly tracing through things but I
know that there must be a wealth of information on this unit out there
as it is quite popular and quite loved by many. So if anyone out there

has pointers for tracking down these issues I would be eternally
grateful.


Thanks,


-Joe

 

[Andy Cuffe]

The unit I have will play tapes but it has the following issues:
1. When the power supply is loaded during playback or record there
is a relatively load static buzz sound coming from the power supply.

There are a few caps on the front panel board near the display that
fail. There's a little SMPS there to supply power to the display.
Replacing these caps helps, but I was never able to completely
eliminate the buzz on all the 1980's I've worked on. I'm starting to
think some power supply buzz is normal for this model.

2. I get chroma noise in the form of diagonal color bands over the
entire frame of video when in playback.

I've seen several with this problem. In both cases it was caused by
bad caps on the TBC board. Every single surface mount electrolytic
had high ESR. The good news is that they weren't leaking, so
replacement was pretty easy.
Andy Cuffe

[email protected] <-- Use this address until 12/31/2005

[email protected] <-- Use this address after 12/31/2005

 

[Joe]

Andy,

Thanks for you response. By the TBC board I take it you mean the
digital video board that is fead by the analog video board. I do not
see
any visible signs of physical leaking. I almost wish they were so I
would know exactly where the problem is. I was thinking of getting
an ESR meter like the EVB unit to help track down the bad cap.
Other and shotgunning all the electrolytics do you have any
recommendations for finding which need to be replaced? Would you
expect to see ripple on the bad caps with the unit in playback and
if so how much ripple would make you change a cap?

Thanks once again for your input!

-Joe

 

[Andy Cuffe]

Andy,

Thanks for you response. By the TBC board I take it you mean the
digital video board that is fead by the analog video board. I do not
see
any visible signs of physical leaking. I almost wish they were so I
would know exactly where the problem is. I was thinking of getting
an ESR meter like the EVB unit to help track down the bad cap.
Other and shotgunning all the electrolytics do you have any
recommendations for finding which need to be replaced? Would you
expect to see ripple on the bad caps with the unit in playback and
if so how much ripple would make you change a cap?

Thanks once again for your input!

-Joe

The TBC board is the one enclosed in a metal shield. The 3 or 4 I've
seen with this problem needed every single cap on the TBC board. I
didn't even bother testing them all after the first 10 were open.
Andy Cuffe

[email protected] <-- Use this address until 12/31/2005

[email protected] <-- Use this address after 12/31/2005

 

[Joe]

Andy,

You were right, I see all kinds of bad caps on this board. Can you
recommend a line of replacement caps? I have no idea who the original
manufacturer is but I would rather go with something that others are
happy with and something that I can get from Digikey or some other
vender that will sell small quantities.

Thanks,
-Joe

 

[Andy Cuffe]

Andy,

You were right, I see all kinds of bad caps on this board. Can you
recommend a line of replacement caps? I have no idea who the original
manufacturer is but I would rather go with something that others are
happy with and something that I can get from Digikey or some other
vender that will sell small quantities.

Thanks,
-Joe

I just used what I had on hand (they weren't surface mount caps).
This circuit isn't stressful on the caps, but the board does get hot,
so 105° caps wouldn't hurt. I did notice that the few through board
caps on the TBC tested fine for ESR. I've never liked SMD
electrolytics because they don't seem to last.
Andy Cuffe

[email protected] <-- Use this address until 12/31/2005

[email protected] <-- Use this address after 12/31/2005