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PSU and amp module update

Started by Will, January 14, 2022, 03:11:48 AM

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A few months ago my piano amp was not working at all. I assumed the power supply was faulty. I ordered parts to restore the power supply and amp modules and made the change. It is working fine now. Here is a report of what I did, for the record.

My piano is a 73 suitcase Rhodes Mark I piano ref. 3077. No upgrades have been done on this power supply or on the amplifier modules so far. It was time to change all the electrolytic capacitors. I also changed the twisted wires to suitable 0.5ohm resistors. I did not change the transistors.

You will find a picture of the finished product here. Zoom in for details :

The part list. At the end of each line, what I ended up choosing.

Amp   capacitor   Electrolytic   C1   4,7uF / 25V NP       AXIAL    >>> Mundorf BG50 4.7uF 75V      
Amp   capacitor   Electrolytic   C2   1uF / 16V NP          AXIAL   >>> Mundorf BG50 1uF 75V   
Amp   resistor   Wirewound   R18-R19 R20-R21   0,47 ohm  -  5W      >>> Royal 0,47 ohm 5W
PSU   capacitor   Electrolytic   C1 C2   1000uF – 35V - 60 mm AXIAL   >>> Jamicon 2200uF 35V
PSU   capacitor   Electrolytic   C3 C4   500uF  -  15V - 40 mm AXIAL   >>> Vishay BC-021 470uF 25V
PSU   capacitor   Electrolytic   C1 C2   11000uF – 40V – diam 50 mm    >>> F+T GMB 33000uF 40V

It costed me 52 euros inc. VAT + 8 euros delivery = 60 euros in total ie. US$ 69 in jan 2022.

The Vishay 1000 uF were not available at the time of purchase so I ended up putting Jamicon spare cap I had from a PSU kit. Not the best choice. I will change them next time.
I left a gap between the resistors and the PCB when I soldered them. Those components are likely the get hot so they need space to dissipate heat.
I soldered an insulated terminal to the wires connected to the 33 000 uF capacitors. They have bolts.
I cleaned the PCB with 95% alcohol, a toothbrush and a tissue to remove flux.
The amp +/- rail shows 28.6V and the preamp rail shows +/- 14.6 V. Good !

Feel free to ask if you need more details.


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