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
Hi Guys,
I inherited a B&O set from my grandfather; BM5500, beocord 5500, Beogram CD 5500 and a Beogram 9500 with penta speakers.
First I had some issues with the CD player, which after some research was just changing a faulty cap and got it working again.
Then I got a bit too confident I'm afraid. the Beomaster's sound had issues. when it went up higher than a certain volume (26) the BM turned off. After some reading I figured out it could be dirty potentiometers so i tried to clean them with deoxidant and moving them about a bit (some of you probably can guess where this is going)
So things went wrong, apparently i didn't set one of them properly back to the old position (I presume), cue in small spark. me freaking out and unplugging immediately.
Result, one channel works now (with full volume) other channel gives a loud hum, no music sound.
I have been teaching myself on capacitors and schematics, have decent soldering capabilities, but this is getting above and beyond my abilities without some help. So a couple of questions.
How do i diagnose with a multimeter where the problem lies in the busted channel?
Do i do a full recap of the PSU board to be sure? Or do I buy a second hand new PCB? there are no obvious burn marks on the board.
Any help is greatly appreciated because this particular set is of great value to me :)
Replace all components in the affected channel. (Or find a replacement amplifier module from a donor Beomaster of the same type).There will be many bad components after a run-away or a short and even components that still measure fine willpotentially have experienced overloads and fail soon.
You cannot put idle current trimmers "back in the position they were". The adjustments are so delicate that 1/10 mm on the resistive track matters a lot.You WILL have to replace the trimmers and you WILL have to measure and set them as shown in the servicemanual.
Too high idle current will heat up the output stage (and use A LOT of power from the mains), eventually it will destroy the output stage.Too low idle current will cause crossover distortion and the risk of burning the tweeters in your speakers will be very high, even at what seemsto be a fairly normal listening volume.
Martin
Thank you Martin,
Definitely learned my lesson.
Do you know a good source for quality compononents?
Many thanks for the help!
Philippe
Do you know a good source for quality components?
Any good component supplier will have what you need, - but I suggest you find a replacement amplifier modulerather than attempting repairs. These DC-coupled amplifiers can give even trained tech guys a good run for their money, anddonor machines are neither difficult to find nor expensive.
Hi Martin,
Following your advice, I got myself a replacement module.
Thank you for the advice!
Kind regards