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 everyone!
Yesterday I had a crazy recapping session through all my Beomaster 8000 (except the capacitor under the CPU cover, I didn't trust myself to open that). Cap kit from Martin, of course! :) I put it together again after some suspence moments (no display at first, because I didn't reconnect the diplay board tight enough and such things). It looks stable now and I can listen to the radio though headphones (I'm restoring the Beovox 8000 at the same time, I can't test the Beomaster with them yet). I didn't do any adjustments yesterday and I'm wondering if it would make sense to do them today. (But... I'm so happy that it still works and I didn't do any bad mistakes! Very few caps were badly out of specs, but all were on the upper capacitance limit (mostly +50% at least) and three from the output stages are totally dead - no reading whatsoever connected to a ESR/capacitance meter after removal).
Offset output amplifier (the only thing I can measure without re-opening part of the Beomaster) measured according to the Service manual gives values of 25 mV (left) and 26 mV (right), but since more than half an hour this values are slowly going up (at turning on the meter reported something betwenn 5 and 10 mV). Now it moves very slowly, but I feel it's not totally settled yed.
The area over the display gets warm quite quickly - I don't think it's quicker than before the recapping, but still: should I check something? I would feel "better" if it would stay a bit cooler.
With headphones connected (Sennheiser HD545) I can hear 50 Hz hum on the right channel, not connected to the volume setting (doesn't change). (This is not a problem, actually: the headphone output was almost before the recapping, way too noisy).
If I turn the volume knob up and down with no input connected I can hear a small noise in the headphones at every "step" of the display. Probably no problem and probably impossible to hear with loudspeakers, unfortunately I don't have an oscilloscope and I cannot check the volume control offset as described in the service manual.
Almost last stuping question: if I decide to open the Beomaster again, in order to check the no-load current... Should I connect the multimeter to both sides of the same emitter resistor (plus right, minus left of the same resistor) or should i connect the meter like plus on R236, minus on R237, on the same side? Totally stupind question, I know...
Last question: is there a way to set the Beomaster 8000 to 240 V instead of 220 V? I never get less than 235 V here in Basel.
Ok... The Beomester has been on until now... Let's check the offset current again... Uhm: 26.7 mV (left), 28.8 mV (right). It's still going up. Does it make sense to open everything again and adjust the potentiometer 5R200 a bit? Right heatsink on the back (underside) hotter than the left one. I should definitely check that no-load current...
Thanks for any help - and here thanks again to Martin (dillen) for helping me through the process yesterday night.
Have a nice day!
Marco
Ooops... I meant Beovox MS150, not Beovox 8000! :)
Hi again!
So... I thought a bit more about the no load current measurement and did it right - of course measuring the two sides of the same resistor. So... I got these values (only one resistor checked on the left channel, so I don't take apart the Beomaster 8000 completely once more...):
- 0 minutes: left 7.6 mV, right 14.9 mV and 13.9 mV- 15 minutes: left 9.9 mV, right 16.7 mV and 15.4 mV- 30 minutes: left 10 mV, right 17.3 mV and 15.9 mV
Temperature is very fine, right a bit warmer than left but still totally ok. The service manual says that you should set the no load current to 18 mV when the unit is in cold state. Probably it would go up later... But... Should I do it? Or should I better just put the left channel a bit higher, so that it will behave the same as the right one? Any advice is very welcome!
Greeting from sunny, windy Basel,
The manual suggests measuring across the two emitter resistors in series and adjust to a reading of 18mV.This equals 9mV across each resistor and also explains the heat buildup at the right cooling fin.If you aim for the 9mV across one resistor in each channel, you won't go wrong.
I don't remember if you replaced the trimmers but if you didn't do it, I strongly suggest you do sowhen you have the thing apart anyways. The old trimmers are too often found bad, oxidating and losing contact.
Good job so far !
Martin
Of course Martin is right - like almost everytime
The 2 measuring points are marked as TP200 and 201, btw.
Concerning the transformator 30T2 - looks like there are totally different ordering numbers for the 4 voltage versions so no 240V modification possible on the type 1901 220V-Version other than changing the transformer .
Gunther
Dillen: The manual suggests measuring across the two emitter resistors in series and adjust to a reading of 18mV.This equals 9mV across each resistor and also explains the heat buildup at the right cooling fin.If you aim for the 9mV across one resistor in each channel, you won't go wrong.
Thanks!!! I really didn't get that it means 9 mV each resistor... :D I was really wondering why I could be the only one on earth with a Beomaster with too low bias... I'll put it right now. It'll be also much better for the summer... ;)
Here again! :)
Almost everything works - and bias current set right, and offset really to 0 +-1.5 mV - not that bad.
Only not working thing: the "auto tune" position is unusable, it just goes immediately into mute and keeps emitting very short "samples" of sound like twice per second or so, with the frequency number going on and off at the same time. This is expecially inconvenient since the tuner is switching to stereo only when then tuning is perfectly centered, and it's a bit annoying to manage this all the time with no AFC. Presets do work flawlessly.
Martin, do you have a magic trick for this AFC issue too? :D
Good night,
One more detail: once I turned on the receiver by pressing a tuner preset button whil on "auto tune" and the amplifier didn't engage (no "click" fmon inside). But the next time it worked - the amplifier startedn, and the tuner produced the "auto-tune-illness" sound I described in the previous post. Uhm...?
It sounds a bit like this:
http://archivedforum2.beoworld.org/forums/p/5230/50034.aspx#50034
Thanks again Martin.
Could be that it is similar to that, but I'm wondering if it could be just some adjustment, since the MPX light works right when a station is correctly tuned in the manual mode (also with lower signal stations) and with auto tuning the receiver is not totally silent, it keeps swtiching the muting on and off. The auto tune was working perfectly before the recapping, so I'm wondering if a slightly different capacitance somewhere may require adjusting.
Here is what is happening after more accurate observation:
1) turn on with preset xx in manual mode: MPX on, stable, perfect sound, signal indicator to the maximum;2) switch to auto tune: maybe on second of flashing MPX light and intermittent sound, then muting;3) switch again to manual: sound comes back, but with no MPX light and mono sound; adjust the tuning wheel a little bit clockwise and the MPX is stable back (no change in the frequency display)
If I turn on the receiver in auto tune mode everything starts from step 2 above. This behaviour can be experienced indipendent from the station and preset number, always the same.
If I turn the tuning wheel in auto tune mode, the receiver is basically behaving like in step 2 above avery time it finds a strong station.
My idea: could it be that the AFC circuit is taking the perfect tuning achieved in manual mode and pushig it a little bit "counter-clockwise" (taking the tuning wheel as a reference) as soon as I switch auto tune on? At that point the muting is stepping in, since the station is not correcty tuned in anymore.
Is it possible that by slightly adjusting 2R24 the auto tune would fetch a little bit more "clockwise"? Or is it something related to the "detector" as described in the service manual? Or maybe I'm totally wrong and it has to do with that IC as you already experienced...
The tuner is sounding wonderful in manual mode and I know that I have no chance of making a complete adjustment of the tuner module without some expensive instruments, but I may try something if that's not going to modify the settings of the manual tune mode. Are the "detector" and 2R24 settings going to change things in manual mode too or not?
Thanks, have a nice Sunday!
M
The LF353 IC is a notorious troublemaker.It can fail in many ways;It can generate noise, clicks, bangs, hiss etc.It can lose gain and start a DC driftIt can become intermittent or play completely dead.
It's a very cheap component and not all too difficult to replace.I would suspect an LF353 over a trimmer that has gone out of adjustment by itself anytime.
Hi Martin!
Thanks for the explanation and sorry for the long post above - I thought that the new capacitors on the tuner board may have made some very small adjustment required, since the auto tune was working correctly before the recap. I think I'll leave the tuner like this for now (it is totally usable and sounds very good) and with no hurry investigate what the problem is by trying a new IC.
More important, I think I'll have to check again the bias of the right channel, since it's again running a bit hot...
Thanks again,