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
Just as soon as i got the lid back on, new issue : Sometimes the sound mutes, when i turn the volume up. Only if i touch volume up shortly, like nudging a single step up in volume. Keeping the finger on volume up and it works just fine. Volume down doesn't have this issue, at least i have not been able to provoke it.
I desoldered and measured all transistors out on the volume PCB (#3), all measures out OK. All diodes too.I have 18V/100kHz at 3C11/C12. Voltages on the 'input' side of 3IC1 seems to be fine according to numbers on the diagram. Haven't touched the output side of the MC14516 yet.
Any suggestions as to what can cause this and/or how to troubleshoot this ?
Beogram TX, Beovox S45, Beovox MC 120.2, BeoSound 1, CX50, Beovox S75, Beomaster 2400, Beomaster 5000, Beogram 5005
Not sure this is troubleshooting progress, but tapping 'vol up' will activate the mute circuit. Can be reproduced from when volume has been off completely and until there is 'a little' voltage out of the counter (3IC1) pins QA-B-C-D. The scope screenshot shows the mute out signal, PCB3 between 3R28 and 3R28a. Far left volume is all the way down, tap 'vol up' slightly and 'mute' goes 'high' or 'on'. Then mute is 'released' when i tap 'vol up' more firmly. Finally mute is activated again, with a light tap of 'vol up'. This can be reproduced quite easily.
On the subject of the 2400.
What is the recommended bulb replacement?
5mm 12V/1W ?
Honestly ? I don't know. I bought them as a 'Beomaster repair kit' and no markings. Try do a search, lots of discussions about the lamps.
jesperb:Try do a search, lots of discussions about the lamps.
I know, and that is exactly why I am asking. A consensus seems to be missing...?
I remember Dillen hinting at the original parts list as being wrong...
...i go my lamps from Dillen (too).
Got a little spare time, which immediately went into the Beomaster 2400 on the kitchen dining-room workbench (no room for guests this week).Looking at the 'volume up mute' issue, where volume would play briefly and then mute for the first 3-4 taps on 'vol up', I measured out 'any and all' voltages around P3 and P5, all voltages matching the values on the diagram. Finally I gave up analyzing the muting diagram, couldn't quite understand it anyways and decided either 3TR3 or 3TR5 should go. Mainly just because they are both involved in muting and the diodes and voltages around them, had all measured out fine. 3TR5 (BC547B) out and in with a new BC547C and now 'volume up' works. Old BC547B tested out fine on the PEAK DCA-75 but the legs were 'rusty' so maybe just a 'tired' tranny
Final issue left to fix : Loud hum in the earphones which disappear when i touch ground, so maybe a grounding wire desoldered itself somewhere? I see no caps left to recap in the signal path from tape-in to the headphone plug. No hum when playing on speakers. Voltage selector is at 220V.
I thinks this project is almost done. Did a FM tuner check yesterday, reception is surprisingly good, with only a short length of 0.75mm2 wire pushed into the antenna plug
Only headphone hum left to fix. Tried two different jack-to-mini-jack converters and 3 different headphone types so an issue with the electronics.
Cannot find any shorts or loose ground wires, the Tape-In DIN plug is rock steady in place.Hum increases when i touch the metal end of the electrolytic caps on the sound control board and almost disappears with volume down (=mute).
Not sure if that would be an indicator ?
Will give it a final troubleshooting try and - even if the remaining hum will hurt - wrap it up.