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
Hello
I am new to the forum, but have already read several threads on here, and is seems like a great community.
I am having a problem with my Beocenter 5000 (type 1802). It switches off after a couple of minutes of play. After reading on this forum, I have decided to try and measure and replace the idle current trimmers R224 and R124.
I got a hold on the service manual, and it states that i should measure the idle current between 3TP200 and 3TP201. I have found TP200, but cant find TP201.
Can someone point me in the rigt direction in measuring the idle current.
TP200 and TP201 are the two ends of R226.
Martin
Hi Martin
Thank you very much.
I get a reading of 5,3mV on R226 and 8,3mV on R126. Are these typical readings when you have faulty Idle current resistors?
I got new trimmers available, a decent soldering iron, and lots of eager to learn.
I have worked in automation (robots, industrial machinery etc) so I understand electricity in general quite well. Electronics is a new found hobby of mine. I understand the general terms, and how voltage, current, resistance etc affect each other, but lack understanding in the design of electronics.
It's a bit low on both channels.Replace the trimmers and adjust to the correct setting.
Do one channel at a time and start with the new trimmer set in its center position.With the Beocenter at room temperature (no warm cooling fins) connect your meter, be ready to adjust and power up.Set it to the correct reading.Keep an eye on it for the next couple of minutes, and adjust if it creeps away from the correct setting.After apprx. 5 minutes the reading should be fairly stabile and you're done.If the setting is stated as f.e. 10mV across one resistor, don't be scared if it moves a little up and down. It's rare to see a completely steady idle within the first 10-20 minutes - and sometimes even after that. A few 10ths of a mV up or down is acceptable.If it runs astray, power down immediately.If after a few minutes it still keeps creeping upwards, there is a problem to be repaired . most likely a bad thermal contact from the output stagetransistors to the cooling fin, or from the temp. sensing component to the cooling fin - but there could also be other reasons.
If the Beocenter powers down by itself, it's often because a little DC is found on the speaker outputs. This typically comes from thesmall signal transistors in the differential amplifier at the amplifiers input growing away from eachother hfe-wise from aging.They should be reasonably closely matched (from the same production batch is usually fine) and sit reasonably close physicallyto eachother to make sure they work under identical conditions (because a transistors current amplification increases with its temperature).
You can check this by fitting a DC voltmeter across the speaker output (one channel at a time) and look for DC.Anything more than 5-10mV is bad.