Probelm restoring power supply.

Thread Starter

Eddy67716

Joined Sep 28, 2020
22
My organ has a power supply and it has been deteriorating lately. There is an IC and some relay's that control the speakers and they, or a component that deals with them; are not working.
I have replaced the 4 main capacitors for the 27 and 38 volt power sources, but the voltage is a bit higher than it should be. The +38 and ground measures 44 volts and the +38 and -38 measures 90.
The 27 volt supply measures has a similar problem, measureing about 33 volts from +27 to ground and 55 volts from +27 ton =27.

I have the schemetics attached below and a photo of the board.
The components on the bottom right are the audio protection circuit that is malfunctioning.
 

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AlbertHall

Joined Jun 4, 2014
11,400
As the 38V and 27V rails are not regulated, it may just be that the fault, whatever that is, results in less current being drawn from these supplies and hence the voltage rises.
 

Thread Starter

Eddy67716

Joined Sep 28, 2020
22
Since I only have a small knowledge on circuitry, I need to know a few things. Should the +38 and -38 values read 38 volts with a multi-meter, or twice the voltage?
I measured the voltages with a multi-meter with the loads unplugged, would that give inaccurate readings?
Also, would the variable resistors to the left of the power supply help with regulating the voltage on the AC side or the DC side of the circuit?
 

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Last edited:

drc_567

Joined Dec 29, 2008
1,135
... Sorry about the previous post referring to misinformation about the voltage selector.
A more careful inspection of the schematic shows that the line voltage adjustment is performed by wiring the voltage selector terminals in a certain pattern, according to the prevailing mains frequency, and not any sort of rotating switch.
... With that in mind, would it be possible to give the geographic location in which this device is to be operated, or the value of the mains voltage, such as 240, 120 volts? ...This is to confirm that everyone is on the same page, so to speak.
 

bertus

Joined Apr 5, 2008
21,452
Hello,

As said, part of the power supply is unregulated.
Organ Power supply unregulated.png
The +38 Volts should be measured between the white and violet wires.
The -38 Volts should be measeured between the white and grey wires.
The +27 Volts should be measured between the green and beige wires.
The -27 Volts should be measured between the green and orange wires.

Bertus
 

Thread Starter

Eddy67716

Joined Sep 28, 2020
22
I have replaced a couple more capacitors that are linked to the TA 7317P IC and I ran into a problem. The two non-polar capacitors at 33 uF 25 volt in the circuit, I ended up getting that value in Polarised electrolyte capacitors instead.
Would that pose a problem if I solder them in with the negative pins connecting the ground traces?

According to the TA7317P data sheet it would be fine because it uses polarised caps, but I would rather be safe than sorry.
 
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