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,

Marco

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 so
when 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 wrote:

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,

Marco

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:

/forum/general-discussion-and-questions/recent-repairs#post-1991252

Martin

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