Technics SU-G50 - Blowing Fuses - looking for a schematic

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Vinster

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Joined 2016
Like the title states, I'm looking for the schematic for this. I picked one up for near nothing so I think it's worth fixing as long as the parts are available.

It's a dead short somewhere as the fuse lights up like a bulb when it goes.

I pulled the power connection between the transformer and the board and the fuse isn't blowing anymore. Getting good voltage from the transformer. (5V from one leg and two 48V[center tap it seems])

There is no visual issues other than the two main power caps have leaked a little. Pulled and metered them and they're close (~9100uF ea, rated at 10000uF)... So right now I'm starting to go through/draw out the circuit starting with the power supply.

hoping anyone here has had this issue and can offer any suggestions (or better yet a full schematic :))

I did get a partial schematic from this thread; http://www.diyaudio.com/forums/soli...mplifer-thermal-compound-okay-power-ic-4.html

any suggestions are appreciated.

Vin
 
V

Vinster

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Joined 2016
Looks like I caught a break. While tracing the circuit and metering continuity I found diode D704 is a dead short (not a visible mark on it). using earth I verified that the chip isn't shorted based on the pic from the thread I linked. only Pins 11 and 14 meter to ground.

The Rectifier Diodes P300D aren't that available but I've crossed it to a 1N5402

P300D; http://www.vishay.com/docs/88691/p300.pdf
1N5402; http://www.vishay.com/docs/88516/1n5400.pdf

Only real difference I see is the reverse current is higher on the 1N5402 vs. the P300D

In the morning I'll get a new set or Diodes and Caps and report back.

Vin
 
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V

Vinster

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Joined 2016
New regulator Diodes and it's up and running. There's something wrong with Channel A, when turned on the sound drops out and it sounds like it's in a hall.

Channel B on it's own seems to work just fine.

Going to start looking at the channel switches after work today.

Vin
 
V

Vinster

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Joined 2016
sgrossklass said:
Look for bad solder joints on the A output terminals, seems like your ground is getting lost there.
Click to expand...

Good call... Channel A Left + and Channel A Right - contacts were both broken...

This amp had a hard life before I got it.

Did some testing and it's outputting 129 watts :) But the fan isn't running well :(

Looks like an 8V DC supply, also wonder what the driver circuit is and wonder if it would be better to have it run a little more sensitive..

Vin
 
sgrossklass

sgrossklass

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Joined 2004
stephan.win31.de
8 V DC? Never seen a fan like that, guess it's a 12 V job? Looks like an axial, but a bit of an oddball shape, rather deep. 50x50x32 or something? I'd try salvaging the bearing on the old one first. It often says what it is on the label, a sintered bearing would require different oil than a standard sleeve bearing or ball bearing job.

HFE has a SM for the SU-G70, maybe that'll give you some hints?
 
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V

Vinster

Member
Joined 2016
Part number on the motor is MDM-4RB4MXA. I can't seem to find any specs on it and I can't find any info on what this motor really is. from Panasonic's site it's been discontinued.

The replacement seems to be this one;https://www.encompassparts.com/item/414723/Panasonic/MDN-4RB4MRC/Motor

I put a drop of sewing gear machine oil on the shaft bearing and it helped immensely.

Running it on a separate supply for now to see how it behaves.

Vin
 
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