Very odd fault with Dynatron Radiogram
I've been servicing a Dynatron RG98 radiogram with a 1375 chassis.
I've serviced the turntable and replaced the belt on the tape deck. I also had to replace the cartridge and fitted an AT95.
The entire radiogram without the speakers is built on a large wooden plinth. The radiograms speakers are plugged into LS1 as are mine when it came into the workshop.
Now the problem.
When selecting DISC (records) there is a loud motorboating sound. Its only there when disc is selected and its loudness is affected by the volume control.
Not being able to sort it out in the customers house, I brought it home.
HOWEVER
It behaved impeccably in my workshop, running off the mains and not the isolated supply.
So I returned it to the customer where again it made its motorboating noise.
I tried the following:
Unplugging the cartridge holder makes little effect
Unplugging the wiring loom from the deck does alter the noise somewhat.
Grounding the inputs makes no difference
Putting a 470nF/275V~ X type capacitor makes no difference
Putting various capacitors across the supply rail in the phono stage makes no difference.
So I've brought it back to the workshop and guess what, No noise at all.
The only difference between the customers home and mine is the electricity supply and the the loudspeakers.
So what is going on and what can I do about it?
|