Topic

Hi all,

I receive a SX-PX1 as donation and want to repair it to keep it in my house. It is really beautiful!

After a quick look in the system the following issues were found:

1- 3 dead keys

I cleaned the contacts and now are working.

2- Volume potentiometer not working.

It’s not possible to adjust the volume, but I can hear it. I tried the HF  jack, line out and effect output. Is that normal?

I dessoldered  the potentiometer from the PCB and it is working.

Other pots in the PCBA are working normally.

3- “Ticks” in the sound

When a key is pressed, a constant “Tick” start and keep for some seconds after the key released.

I could remove it when the input ground pin in the Filter PCB is left floated.(CI LM1894N)

I also noticed that just one channel have this click.

 

I  believe that issue 2 and 3 are correlated. I requested some components to change, but everything that I’m doing is empirical because I could not find a service repair manual or even the user manual.

So, I would like to ask if some have any kind of information to help or where I can download/buy the service repair, I will really greatfull.

Thanks in advance,

Reneé

 

Ps. Later I will attach some photos of what I did.

Replies

Hi all again,

I found the problem and will post here if the solution.

No volume control and ticks sound had the same root cause, and the things got bad when the older owner tried to “fix”.

The root cause was the 10ohms resistor in the main board in series with the -15V input. (Under, right side of the gray connector).

It what open with no visible visible sign of failure. Due to that, some components were left floating and the sound was very low.

To try solve the problem, the old owner change some cables and remove the volume control from the circuit.

Doing that it applies 15V and -15V in the decoupling capacitors before the power amplifier. This was also not a visible failure. The capacitors increased so much the internal resistance and started to produce the ticks. (I don’t know why…)

When I removed the ground pin, I left the opamp reference floating, and that’s why it stopped.

To fix everything, I mapped all the connector of the boards, and noted that both sides of the cables were identical.

To fix, I replaced the open resistor for two 22ohms in parallel (I don’t have one10ohms at home and the shops are closed due to lockdown), replaced the two input capacitors for new ones, audio capacitors(the gold ones) and check all the cables to be in the correct connector.

Doing that everything is working perfectly again. What a sound!!!

 

Best regards,

Reneé