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Panasonic AG-1980 chroma noise/power supply buz

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.

  1. 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

Reply to
Joe
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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.

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

snipped-for-privacy@psu.edu

Reply to
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

Reply to
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

snipped-for-privacy@psu.edu

Reply to
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

Reply to
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

snipped-for-privacy@psu.edu

Reply to
Andy Cuffe

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