Highly distorted sound

[WimJoos]

First of all sorry for writing in English. I can read and understand German, but my writing is .... Be free to respond in German.

I have a B261. A years ago i replaced all caps on the power supply board and audio board. The B261 worked fine afterwards for a few years. Becuase of circumstances the B261 was stored awsy for over 1 year. When I reconnected everything memory seems intact, preset names and frequency are still the same as 1 year ago. But the sound is highly distorded. Especially on louder stations. The distortion is on both channels, but worse on the right channel. The problem is present on fixed, variable and headphoneoutput. What is the most common cause for this kind of issue?
Do i need change the caps on the other boards or do i need to change the potentiometers,...

Thank you for your replies,

[eckibear]

You should check the output "horizontal" on the backside. Some versions of the B261 may not have this output, though it is always available inside. Another way to save 50 cts back then.
It's a RCA/cinch or BNC connector. Connect a high-ohmic headphone (100 Ohm or above) to it. The MPX is the signal right before the stereo decoder. therefore you will hear only mono (L+R). If the sound is clean, the decoder or the output amp likely are defective. Otherwise the demodulator or the IF amp could be affected.
BTW: Do not connect any stereo amp to this output. The MPX signal contains the 19kHz pilot and the (L-R) signal band up to 53kHz. Both could kill either the amp or the tweeter connected to it. Maybe even both...

If you happen to have a scope and know how to use it, you may also inspect MPX signal in combination with the "vertical" output, which represents the rectified RF/IF level in the Tuner. This is also descibed in the user manual. It was meant for detection of "evil" multipath reception and optimization of antenna direction adjustment. In fact, if your FM location is really bad the distortions might come from that as well. however, on some stations it should be better, also in mono operation most of the distortions should vanish. Multipath affects mostly the high FM deviation and high frequency parts of the modulated signal, which transport the channel difference (L-R). The lattter is more or less eliminated in mono operation.

[briscoedjs]

I had this problem on my B261 and I tracked it down to the relay on the audio board. I designed a PCB which has 2 off AXICOM IM7 24 volt relays on it to replace the OEM Zettler AZ7-4C relay. Now there is no distortion and I here a very gentle and satisfying click on startup. PCB designed using KiCad. I might consider selling the PCB design for a pay what you like donation. Please forgive me if I have broken any rules by offering this. Just thought that it might be useful. Working on a replacement OLED LCD display next. It's a lot of work as I have to figure out the CBUS/I2C serial protocol on the bus first using my logic analyser.