Modern Tech help, Laser Disc Repair? - Videokarma.org TV - Video

***Eric H*** · #1 08-27-2011, 02:53 PM

I picked up a Sony MDP-650 at the GW store today, nice dual side machine, works well but the Fluorescent display is dead.

I tried soldering the pins to the display tube but that didn't help.
There is voltage going to the board but I don't know what should be going where. I'm suspecting the display tube itself is bad but don't know for sure.

There's a switch to turn off the display but it doesn't help.

I have seven days to return it, I may keep it anyway since it work well, OTOH I have a couple Pioneers that work well too but this one has S Video and an Optical Audio Output that I don't think the Pioneers have.

Bonus feature, it came with a disc of Star Trek III Search for Spock.

jpdylon · #2 08-27-2011, 03:36 PM

Look on the FP-746 "mode control" board

You should have heater voltage (between 2-4v outer pins -ac or dc on the flourescan) and a negative voltage around -30vdc to drive the grid (check pin53 on IC 102). Often times the grid voltage goes missing due to a failure in the regulated supply or IC.

Also check to see that you're getting +5 and -5v regulated, and that the 8mhz clock is running on the display processor (pin 5,6 IC102). Otherwise the display mode controller won't work and you'll get no display either.

Machine works otherwise?

***Eric H*** · #3 08-27-2011, 05:36 PM

Hi Jordan, thank you for the help.
Yes, it works fine otherwise, I was watching ST 3 on it.

***Eric H*** · #4 08-27-2011, 09:00 PM

Hi Jordan, if by the end pins you mean the two that are off by themselves at each end of the row of display pins then I'm getting basically no voltage, AC or DC.

Using a shield on the Mainboard for a ground I can find 5.0 volts at several locations on the various connectors that go to the board FP-746 but no -5.0v, I can't check pin 53 of the IC because it's just too small for me to work with, I'd blow it up for sure if I tried.

The highest voltage I find going to any of the connectors on the board 746, is -16v measured from the grounded shield on the Mainboard.

Electronic M · #5 08-27-2011, 11:41 PM

I'd keep it if everything, but the display works.

***Eric H*** · #6 08-28-2011, 01:24 AM

Quote:

Originally Posted by Electronic M

I'd keep it if everything, but the display works.

Yeah, you really don't need it to use it. It has on screen display also.

andy · #7 08-28-2011, 01:54 AM

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***Eric H*** · #8 08-28-2011, 04:39 AM

OK I do get a -30v bias from the heater pins to ground, across the pins however, nothing, AC or DC.
I measure about 10 ohms across the heater pins

jpdylon · #9 08-28-2011, 10:33 AM

The heater pins are on the far sides of the FL display. If you're getting DC but no AC, then I would look at the DC/AC converter for the display. Double check voltages on Q101 and 102, but my guess is you have either an open capacitor c101 or c102. This would interrupt the AC to the FL display.

Ed in Tx · #10 08-28-2011, 01:16 PM

Quote:

Originally Posted by jpdylon

but my guess is you have either an open capacitor c101 or c102. This would interrupt the AC to the FL display.

Yep. C101 could be open not charging up to the operating voltage for the FL display, that would be my #1 suspect, or C102 could be open. I would use a low ESR 105°C rated cap to replace C101.

andy · #11 08-28-2011, 02:24 PM

...

***Eric H*** · #12 08-28-2011, 05:47 PM

Wow, you guys are good!

Those caps are located underneath the display with no easy way to access them.

I had a 47@25v cap handy so I touched it across the lugs from the back side, the first one I tried C102 did the trick, the display came on nice and bright!

The cap is located in the top left as viewed from the front, I was able to unsnap the display and bend it down just enough to reach in with a small pair of needle nose pliers and remove the cap, (after de-soldering it first of course) put in the new one and awaaaay we go!

Here's a pic of it working, the guilty cap is sitting on top of the display.

Thanks a million for the help!

***Eric H*** · #13 08-28-2011, 06:08 PM

I made a short video of this thing loading a Disc and reversing.
The display does this neat scrolling thing when you change sides.

I like the sounds it makes when it's winding up, the amount of inertia in those 12" discs is scary.

http://www.youtube.com/watch?v=-62pinqVULg

jpdylon · #14 08-28-2011, 11:28 PM

Excellent! Glad to be of help.

ChrisW6ATV · #15 08-29-2011, 12:56 AM

Good news that you got it working again. I have heard that Sony Laser Disc players have a lot of problems; if it is things like this rather than motor/tracking issues, that is not bad at all. My neighbor has a Sony player (it may be the same one even), and he has been happy with his.

Some day, I need to try repairing my original Magnavision player, and a couple of Pioneers.