Panasonic AG-7750 problem, no power up?

[josje22]

Hi there,

I'm in the middle of a conservation job and this thing happened with my 7750:
I finished digitizing the tape and rewinded it and ejected it. Took the tape out but there was some tape hanging out of the cassette (not broken). Then the machine was powered of. When I switch it ON the drum starts rotating, the front display light up for a second, and then nothing. dead!

First I thought about a bad cap in the power supply unit, but then I read about this (solved) topic:

"JVC HR-S7600AM keeps shutting down after 3 seconds ?"

At this topic you talked about a mechanic failure, or faulty shutdown/power off. Then at power up the machine, the selftest fails and refuses the vcr to start up.

This could be exactly the same problem I have with the 7750.

Is there any knowledge at this great forum to solve my problem?

thanks in advance,

Oskar van den Belt
Amsterdam

-- merged --

Hi there again,

Is there really no experience or eureka memory about how to possibly solve this problem?

thanks in advance,

Oskar

[jwillis84]

I'm no VCR repair specialist

However [shutdowns] are usually the result of some kind of belt or mode switch problem.

The belts are made of rubber and naturally wear out. When they are too old they can't provide enough torque to finish their job, and the microprocessor eventually shuts things off to fail safe.

The mode switch senses loading mechanism position and reports that to the microprocessor. If the mode switch becomes dirty unpredictable things can happen. Usually the microprocessor trys to fail safe when the mode switch isn't reporting properly and can prematurely shut everything off to fail safe.

If the microprocessor didn't shut things off, the tape could unspool in the machine, or it could end up eating the tape. And sometimes they still do unspool or eat tape.

I'm sorry that none of that tells you how to fix your machine.

Unless its an overly tightly wound cassette, the problem is likely to continue or get worse.. until you get the machine serviced.

ps.

I am merely a visitor to this forum and have no special knowledge.

[lordsmurf]

JVC and Panasonic decks are completely unrelated, so a fix for JVC is not a fix for Panasonic. At most, it shares the basics found in all VCRs, like belts and gears.

Most likely, you're going to need to dismantle the machine, with the help of a service manual.

That specific model service manual is not in our archive, but it'd be a great addition if you come across one and attach it to a forum post for others in the situation in the future.

[josje22]

Hi there,

I checked many parts by using the service manual, but could not find the solution. I also checked the caps on the power supply visually, but seem to be ok. For now I gave up, took me too much tiime. The machine is at a service centre right now, and I hope they can fix it because it's a great vcr with a nice tbc.

included as attachment is the sevice manual

best regards,

Oskar

[dpalomaki]

Wonder if it might have a root cause similar to the AG-1980 issue discussed in this thread:
http://www.digitalfaq.com/forum/vcr-repair/6013-panasonic-tape-loading.html

If the mechanism (timing) was left in an invalid state at the last eject attempt it would not Want to power up.

[josje22]

Hi there,

Here update again:
The technician did not solve the problem yet. He checked all the mechanical parts, and they're ok he said.
His thoughts: An electric part of the 7750 thinks that there is still a tape inside, which there isn't, and switches off the whole system.

Any thoughts about where to find the solution? He will spend half a day to try to find and solve the problem. If not, trashcan?

best regards,

Oskar

[dpalomaki]

Mechanism position sensing is by the mode switch (item 1-36 in page398/399 of the pdf).
And tape sensing is typically by photocells.

Does the display give any diagnostic information (page 37 of the PDF, 1-33 of the manual)?

It might be the mechanism stopped moving before completion of the load or eject tape process. As a result the mode switch may have ended up in a undefined state preventing further motion. The system is designed to stop if it senses a jam to prevent further damage to tape. Part of that sensing criteria could be taking too long to change mode switch positions.

If a gear has slipped a cog that could cause issues. The tech should be able to verify the mechanism timing by positions of the gears, and verify that none of the drive parts are slipping on the motor shafts.

[lordsmurf]

Never the trashcan.

It has good heads, right? That alone has value.
And think of all the gears/belts inside.

If you no longer want it, put it on eBay for parts (and at a low cost, like under $50, no something stupid like others do, wanting $100+ for a POS; those people are delusional). Instead of having trash, you sold junk for the cost of a nice lunch/dinner.

Other AG-7750 owners will appreciate you.

[josje22]

Hi there,

The technician gave up. He was really sure that a specific IC chip is broke, but could not find a replacement one. When I get the machine back I can give you more specs about his report. Maybe somebody here can get this chip.

best regards,

Oskar

[dpalomaki]

If the chip is an ASIC it might be difficult to find. Chips are normally mounted on PC boards. You might be able to find a usable replacement board from a parts machine. I see 3 on ebay this AM.

[josje22]

good suggestion, but all ebay machines are in the us. I'm based in Amsterdam, so too pricy shipping.
But thanks for the idea.

Oskar