Panasonic AG1980P power supply problems

[captainvi...@gmail.com]

I have 4 of these that we still use here in the house. Last year we
were operating on generator power after a storm, The generator started
surging as it began to run out of gas and I later learned that three
VCR's power supplies were wiped out I'm guessing from this. Luckily I
had three junkers that were kind enough to donate power supplies and
since the power supplies are separate plug in modules I was able to
restore the three machines relatively easily.

The other day we had a 10 second blackout with surging during
restoration. After power came back on I noticed that one of my
machines was again dead. I have the service manual however this power
supply is a nightmare to get into whats more take apart and try to
troubleshoot. I never had to deal with this after the first blackout
when I just did organ transplants. The chassis is soldered together
and the two boards connected with jumpers and then the entire mess was
soldered together afterwards. For a commercial machine from a service
stand point this is a piss poor design.It's not something I'm looking
to rip apart.

I was really hoping that perhaps someone who worked on these units
back in the day may remember power surges causing any particular
problems with these power supplies. That way maybe I can squeeze in
there and get at just what I need to without having to remove a bunch
of stuff in order to get to it.

So now I have 4 bad power supplies that actually may all have the
same problem and I'm not sure what I'm going to do. If anyone can
please help me with this I would sincerely appreciate it. Thanks,
Lenny

[John-Del]

They used to offer kits for these. They included the Mosfet/Transistor, driver, ref IC, a bunch of zeners, and all the capacitors in the primary and secondary. It's normally high ESR caps in the primary that wipe these out. As long as they're plugged in and warm they're happy, but if they lose power and go cold, they'll blow the mosfet as soon as power is restored.

Email my brother and see if he has any supplies left for these. I know he got rid of a lot of stuff but you never know. If you find one somewhere, make sure you recap it before plugging it it.

[Chuck]

On Mon, 8 Apr 2019 13:22:09 -0700 (PDT), captainvi...@gmail.com
wrote:

Lenny,
Once you recap these and replace the mosfet, please check the 18V
zener to ground on the 15V line. Very likely that it will be shorted.
Chuck

[captainvi...@gmail.com]

On Monday, April 8, 2019 at 4:22:12 PM UTC-4, captainvi...@gmail.com wrote:

Chuck
In looking at the schematic I don't see an 18V line. At the output there is a plug. It has outputs of 4.0V, 6.0V, and 14.60V, but nothing marked 18V. Actually, the only zener I see on the board is D1018 and it is off the emitter of Q1006. Could that be the one you're referring to? Also I heard that some parts stores were selling repair kits for these but that was a while ago. Do you know who might still have these available or at least where I could still get the Mosfet? Thanks, Lenny

[mako...@yahoo.com]

Looks like the schematic is available on line.

I would DL the schematic and rip one of the four apart and try to fix it.
Then decide about the other 3.

mark

[Chuck]

On Tue, 9 Apr 2019 10:58:05 -0700 (PDT), captainvi...@gmail.com
wrote:

Lenny
Though I worked on many of these units, I confused this P Supply with
a different Pana supply that had crowbar protection on the 15V line. I
would guess that IC1001 is bad and I don't know of any kit that is
available. Chuck

[captainvi...@gmail.com]

On Monday, April 8, 2019 at 4:22:12 PM UTC-4, captainvi...@gmail.com wrote:

Chuck, John Del had a novel idea. He said if the mosfet was good and even if the caps had bad esr I might be able to get the supplies to start if i heated them up. I used a heat gun on this one supply and then connected it to the VCR and to my utter amazement the unit came on. I dumped power a few times and each time it started up, so that was a really good tip. The caps all check good but I suppose that I should replace them anyway. Do you have a good source for good,
(Nichecon or equiv) 105 degree caps? Thanks, Lenny

[jurb...@gmail.com]

>"In looking at the schematic I don't see an 18V line. At the output there is a plug. It has outputs of 4.0V, 6.0V, and 14.60V, "

He was probably referring to the 14 or whatever line that usually has an 19 VZD for protection. Might even be 12.

THAT line is what you test. Silly techs I met checked the 5V, which is not that good an indicator because it is on the feedback loop. As the output goes down in that supply all the others go up. The 12 or whatever volt line is a first thing indicator. BEFORE it blows up. If it is over 14V then you need the 5V caps.

Some more complex feedback systems have been used, as well as MOSFETs instead of bipolars, but the 5V as far as I can see FEEDS the opto, which is the main control mechanism. It supplies the drive to the chopper to regulate. When the load increases or the line voltage drops the frequency drops and more current is applied to the primary of the transformer thus increasing output to compensate. The opposite happens when the load decreases or the line voltage increases.

You CAN see the action of this system by connecting hot and cold grounds together, using an isolation transformer that is variable and find some sort of dummy load(s). People go "EGAD" when I sat connect hot and cold grounds together but you can do it. You NEED an isolation transformer, and do not connect it to anything else. I have done it many times. But I can go with the scope to both hot and cold sides and actually see just how the feedback works. I found it is much simpler than it seems.

One of the MAIN things about those supplies frying out on the absence of secondary filters is on the drain or collector of the output. In the old days it was 4.7uF/250V. I have also seen 10uF. If that cap opens it destroys the chopper. It is not hard to find, follow the cord through the rectifiers and to the primary of the transformer. Look at the "C" or "D" terminal of the chopper and you'll find a lytic. That is critical, no matter what else is going on with it.

Nuff for now. Give me more detail and I will give you more detail. I can't give detail when I didn't get any.

[Lucifer]

On Wed, 10 Apr 2019 12:58:15 -0500, Chuck <c...@dejanews.net> wrote:

>On Tue, 9 Apr 2019 10:58:05 -0700 (PDT), captainvi...@gmail.com
>wrote:
>
>>On Monday, April 8, 2019 at 4:22:12 PM UTC-4, captainvi...@gmail.com wrote:
>>> I have 4 of these that we still use here in the house. Last year we
>>> were operating on generator power after a storm, The generator started
>>> surging as it began to run out of gas

Were you able to switch back to petrol to keep it going?

Sounds like he needs surge protection or a UPS.

Some early generators will interact with switch mode power
supplies causing them to surge.

[John-Del]

They'll read much better when hot so it's best to check them when cold. In any case, checking ESR in circuit isn't foolproof. Today we run into low ESR smd low value caps bypassing high value electros and fooling the ESR meter.

Since these supplies run 24/7/365 and are stuffed into an enclosed and tightly spaced can, they're well beyond any reasonable expectation of hours. Change every electo in the can and you should be good for another 10 years.

[Chuck]

On Wed, 10 Apr 2019 11:18:33 -0700 (PDT), captainvi...@gmail.com
wrote:

Mouser Electronics. They also carry Panasonic 105C caps which I
prefer.
https://www.mouser.com/?gclid=CjwKCAjwy7vlBRACEiwAZvdx9ktqhBZeToY8xAakH1D_8EGpj_EkO3NURTkAVIRR_2dI9T7_RgfMrxoCG0UQAvD_BwE
John's idea does work on this supply. The one I was thinking of would
have had the shorted 18V zener so it wouldn't start. Good luck with
the other supplies. As JUR6006 says, the 5V line caps are definitely
bad. With an ESR meter, you'll probably find others. Good luck. Chuck