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Technics pr702

I have a Technics pr702 no sound from speakers only headphones, I was told the problem is in the main board, audio gate not opening at boot up therefore mute/demute not working, is there anyone out there know of a board for this model or could possible r…

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Technics pr702

mrbassman

mrbassman
United Kingdom

Total Posts: 4
Joined: February 18, 2018

I have a Technics pr702 no sound from speakers only headphones, I was told the problem is in the main board, audio gate not opening at boot up
therefore mute/demute not working, is there anyone out there know of a board for this model or could possible repair board?

Tags: audio problem
Attachments: IMG_1055.JPG
Posted on February 18, 2018 at 6:35 AM
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6 Replies

davetutt

davetutt
United Kingdom

Total Posts: 166
Joined: January 12, 2015

Re: Technics pr702

Mute is fine if the headphones work as they are both derived from the same point in the circuit. If I remember correctly the speaker output on that piano is actually an early class D design with a pair of MOSFET output devices per channel. I can't remember if the headphones are actually separately driven from the low level circuitry but the switching function of the headphone socket is critical as if you don't have switching it will kill the speaker output. I hope you have removed any jack adaptor from the headphone socket as if you leave it in it will stay on headphones even if you haven't got them plugged in!
I have so far only had to repair one of these output stages so there is very little chance of there being a fault in this stage. It is robust and reliable.

Dave Tutt

Posted on February 18, 2018 at 9:07 AM

mrbassman

mrbassman
United Kingdom

Total Posts: 4
Joined: February 18, 2018

Re: Technics pr702

Dear mr Tutt,

This is the reply I got from another technician.

John Freeman

Attachments: C0CD68E2-0FC0-47DA-BAAD-642E8BD0CC70.png BB975AB1-A2FD-4CA0-98B3-0C8149E0BACA.png
Posted on February 19, 2018 at 9:47 AM

davetutt

davetutt
United Kingdom

Total Posts: 166
Joined: January 12, 2015

Re: Technics pr702

Unless its plain text I won't open stuff left here like that. There is no way that the muting is effecting this as they both come from the same point.
Have you left a 3.5mm to 6mm jack adaptor in the socket? If you havent then its either the socket itself or the power amp. Try plugging in an amp on the rear panel line outs. If it works here then its the power amp.

Posted on February 19, 2018 at 11:31 AM

mrbassman

mrbassman
United Kingdom

Total Posts: 4
Joined: February 18, 2018

Re: Technics pr702

Dear mr Tutt,

Thanks for the reply.
Their is no jack plug left in socket, I did what you said and plugged it into an amp, that works fine,so
As you said it must be the power amp and the transistors. On the board their are two heat sinks, one sink has two transistors the other has four,are you saying I need to fit all 6 transistors and would that make it work, if it needs more work could you repair it?
John

Posted on February 19, 2018 at 12:29 PM

davetutt

davetutt
United Kingdom

Total Posts: 166
Joined: January 12, 2015

Re: Technics pr702

from your picture the bottom heatsink is where the correct transistors live. The driver circuit for them is on the adjacent board plugged into the main board. This contains all the circuitry fore the class D output. I would suggest you look for some circuit protectors first as these are very delicate fast acting devices and it is likely they will have blown if anything is wrong with the amp output. They are usually pale green and are less than 8mm long and are usually marked on the board with the value.
They sometimes look like resistors and in this case are standing on their end next to the upright power amp add in board. I would think they will be open circuit. Sometimes putting new ones in brings it back with no other faults. If I remember correctly they are 1amp ones in these piano's. There are also two fast ICP devices that look like transistors. These need to be checked too as they will have failed if the output devices are dead. In your picture they are above the heatsink.

Can you do this yourself or do you need to find someone to do it for you?

Posted on February 19, 2018 at 1:01 PM

mrbassman

mrbassman
United Kingdom

Total Posts: 4
Joined: February 18, 2018

Re: Technics pr702

Dear mr Tutt,

Thanks again for reply.
If this is a possible repair could you do the job for me,
if so would you need both boards sent to you?
Also could you give me some idea on cost for repair.

J. freeman

Posted on February 24, 2018 at 6:55 AM