ARCHIVED FORUM -- March 2012 to February 2022READ ONLY FORUM
This is the second Archived Forum which was active between 1st March 2012 and 23rd February 2022
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
Missing 8Vref.Usually a shorted capacitor C417 (470uF / 10V).
Martin
Spot on!
I did not have a 470uF, but guessed that if it was shorted then replacing it by a 100uF capacitor would not cause any harm, since its purpose is probably only getting the ripples of the DC ref voltage here.. So heating up the soldering iron, get the culprit out and a new capacitor in did the trick.
I will get a real 470uF before I reassemble the recorder, but right now it works fine.
Do you think it makes sence to preventively replace other capacitors too?
Thanks a lot !
Bert
Curiously, this is about the only capacitor going wrong in these Beocords.It's rare to see other components fail.- Apart from belts and the general cleaning and lubrication of course, which should always be done.
strange indeed...
But what about any other capacitors in the 4500 series?
I have seen some advice about preventively replace electrolytic capacitors... (particularly the larger ones from the power supply components)
BTW the fix was dead-easy, much better than replacing IC’s (which was a wrong diagnose anyway ;-))
Great to be a member of this forum...