I inherited a complete B&O 4500 series system two weeks ago. Beomaster 4500, CD player, Beogram, Beocord, Cx100 speakers and a Cona. I am delighted with the set...

First I refoamed the speakers. They are in top shape again, great result and a cool job to do.

Then checked out the rest, turns out that the casette player is not working properly..

I really would like to fix this.

The symptoms are :

Pressing play starts the mechanics allright, however no signal at the output. The led playback level bar goes to “full” (all leds light up).

I opened the device and downloaded the schematics. All mechanical functions and the tape control logic works just fine, also data exchange with the beomaster works as expected. At the input of the Dolby IC LM1131C i measure a normal audio signal. (measured using a digital scope) The output pins should, according to the schematics show a 10 x stronger signal (on pins 9 and 12, TP9 and TP10) but show nothing.... The power supply to the IC is normal.

Questions:

Anyone an idea what is wrong here?

Is there besides the schematics any repair manuals (like a step by step troubleshooting guide)?

Has anyone seen this or a similar problem before?

Removing the B board, and then play back does not light up all the LED’s, but flashes them briefly and there is a very weak audio signal (good, but very faint). 

For me the Dolby IC or IC3, which controls the signal switching to the Dolby IC (?) are primary suspects, but before swapping them (where to buy the LM1131C in the first place?) I would like to ask if anyone has dealt with this before.

(Normally I would suspect power supplies more than audio signal IC’s)

All comments / questions are welcome

Bert Degenhart Drenth