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 Post subject: [MDP-850D] Power Supply Schematic or component list
PostPosted: 03 Aug 2022, 10:08 
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Hi all,

I have an MDP-850D, through some good and bad luck, the power supply is not operating with much more than 100ma load on the +/-15v outputs.

I have the service manual, but the PSU is not described other than in a block diagram in the service manual as it appears to be wholly supplied to Sony by Nichicon.

Would anyone have a working one? or a schematic ?

The issue i have is it was dead when i got it, while probing around to test it to see where/what voltages were present, i slipped and some sparks come out. I replaced a couple of dead caps and a burned resistor, but finding the value of the resistor may not have been correct and it is part of the over current shutdown circuitry, which i suspect is why it won't start with a higher load. With a small load it will start and run, but the resistor in question gets very hot to the point of smoking, so there's likely another fault cause by the arc when i slipped with my probe or the resistor is WAY off in value.

I am interested in either a parts listing, schematic, or someone who has a working one that can identify resistor value(s). I have no idea if the rest of the player works at this point because the PSU damaged occurred before i was able to get it running. When installed in the machine the standby light will come on, but as soon as its pressed and the powerup relay clicks, the PSU just shuts down (because its drawing more than the current it will support).


Thanks !
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 Post subject: Re: Sony MDP-850D Power Supply Schematic or component list
PostPosted: 05 Aug 2022, 23:42 
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See if this is of any help: https://www.laserdiscplaza.fr/forumld/v ... 9&start=15

cozzm0 wrote:
When installed in the machine the standby light will come on, but as soon as its pressed and the powerup relay clicks, the PSU just shuts down

The North American models do not have the Nichicon board, but the above is very common. Have you checked the caps in the board this one feeds? I have had to replace them in the power section of the large main board that folds up as well. They might be in a metal "cage".
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 Post subject: Re: Sony MDP-850D Power Supply Schematic or component list
PostPosted: 06 Aug 2022, 08:39 
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Thanks for the reply, yes i've seen that french page and had already replaced the two small caps that were stopping the PSU from powering on at all originally which is the common issue.

I found that page when looking for information & close up pictures of the PSU to try and determine the resistor value that was fried.

If the power supply can't support 200ma total (100ma/rail) then its not going to be able to power on the rest of the unit was my thought, rather than there being more faults down the line.

I haven't removed the capacitors from the second power/regulator board to test them individually but i've checked them with my ESR meter in circuit and everything looks OK.


R104 was burned and this picture (from the french page) shows it in good detail brown, green, brown so i replaced it with 150 ohms.

https://www.laserdiscplaza.fr/forumld/d ... &mode=view


It was burned when my probe arc'd onto the heatsink while probing the wire link at the top of the board. It was either that resistor or the D108 near it that sparked, but the diode still reads OK (normal drop across it in 1 direction), but i don't know if its 'value' changed as it looks to be zener from the board marking.
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 Post subject: Re: Sony MDP-850D Power Supply Schematic or component list
PostPosted: 07 Aug 2022, 04:15 
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Could it have taken out one of the ICs near it? Not really sure how to debug this without schematics. It would be a slim chance, but you could try contacting Nichicon.
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 Post subject: Re: Sony MDP-850D Power Supply Schematic or component list
PostPosted: 11 Aug 2022, 08:19 
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Rule number 1 ? Visual inspection, then when you have visually inspected, inspect again.

I was inspecting the mosfet and decided to remove it from the circuit to test it and I spotted it. I thought it was some black dust/dirt. When I tried to shift it with my screw driver and it caught the edge of the crack I was angry and happy at the same time. Angry I didn’t see it before, happy that I might have found the issue.

0.22ohm shouldn’t read 1.9K ohm resistance … supports 0.6A filament bulb per +/- 15v rail now. No smoke after 2 minutes. Temporary 0.33ohm resistor in to prove it works. Will get 2W fusible replacement like original and get it back into the machine on the weekend and keep fingers crossed !!


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 Post subject: Re: Sony MDP-850D Power Supply Schematic or component list
PostPosted: 11 Aug 2022, 13:20 
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Very nice!

You might want to see if anything from MDP-800 Repair is applicable. A few should overlap, but give it a good look over for leaks either way.
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 Post subject: Re: Sony MDP-850D Power Supply Schematic or component list
PostPosted: 11 Aug 2022, 21:18 
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The caps on the main boards all look good. I can’t see any signs of corrosion or leaking, black traces or anything. Plugged it in and powered it up with the PSU hanging out the side of the chassis and it powered right up, eject/load, display all works. Wouldn’t read a disc, tried CD and LD, side A and B, disc spins on side B momentarily but no joy. So powered it down and found the laser ribbon almost out of its socket on the PCB. Reseated it and went to power up again and it DEAD. Haha. Not even stand by light this time. PSU outputs nothing at all even with no load. Nothing got shorted this time, no smoke, nothing got hot. Just dead. Fuse Ok, 350v on main cap, 350v at the transformer, nothing else happening. Maybe the overloading from before took its toll on the switching chip. Very odd. Maybe not having it grounded killed it because it wasn’t bolted into the chassis.

Back to the bench !!
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 Post subject: Re: Sony MDP-850D Power Supply Schematic or component list
PostPosted: 13 Aug 2022, 07:40 
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Another Fusible resistor, this time totally open, directly feeing the VCC of the switching IC. Whacked another temporary replacement in 100K R102 and it’s back to life again. Will get the correct 100K 1 watt when I pass by the shop. I hate just buying a resistor here and a capacitor there but I can’t keep stock of all these off parts. I’m now wondering if I should shotgun all the fusible resistors in this thing now or if this was just unlucky. I haven’t had such issues with fusible resistors in the past.
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 Post subject: Re: Sony MDP-850D Power Supply Schematic or component list
PostPosted: 19 Aug 2022, 14:36 
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cozzm0 wrote:
I hate just buying a resistor here and a capacitor there but I can’t keep stock of all these off parts.

Story of my existence. I'll need a $0.17 capacitor, but to pay $8 to ship it.

Is it still holding up?
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