The Workbench

Re: BeoMaster 3400 FM station drift

yachadm — Tue, 29 Dec 2009 02:35:40 GMT

Done!

It was the JFET - Gate and Drain shorted. I had 14.5V on all 3 terminals G,D,S.

I put in a new 2N5245, and now (when the PSU has stabilized at 26.0V) there's G (AFC ON) = -4.18V (SM shows -5.3V), AFC OFF = +14.3V, and D=S= +14.4VDC (SM shows +10V).

I've checked all the components and other voltages down the line in the AFC and detector balance circuits, all are OK, and I can't find a reason for this discrepancy.

The discrepancy is just here at the FET (BTW - the same voltages whether the FET is installed or not (ala BM2000). Then again, the SM may be wrong - the AFC circuit shows the same voltages in both the BM2000 and BM3400, even though the resistor values are different.

Anyway, it works incredibly well - it picks up distant stations in stereo, that other radios which I have, can't even detect - so I'm inclined to call it a completed job, unless I have an inspired thought. (I did do a great alignment job, if I may compliment myself!)

Re: BeoMaster 3400 FM station drift

yachadm — Mon, 28 Dec 2009 08:33:17 GMT

Whoops... not quite done yet.

I engaged the AFC after putting in the ZTK22, and AFC-on pulls the station way off center. Very distorted.

I think that the JFET is no good, as there is 14.5V on both Source and Drain terminals, whether AFC is on or off (instead of 10V).

I'll desolder it in the next couple of days, and try without the JFET at all, as in the BM2000.

I think that I'll have to realign the Detector also.

Re: BeoMaster 3400 FM station drift

Die_Bogener — Mon, 28 Dec 2009 08:20:28 GMT

Yes, there are 2 specs (0.5W and 1.3W) for normal zener diodes and also for the ZTK types.

ZTK were available in 0.5W and 1.3W, but most of them only in 0.5W. Usually the 33V type was a 1.3W, used in TV's, the smaller values were 0.5W.

Because of the price for these ZTK types it is today cheaper to use real regulator chip than a diode for 2 Euros.

Re: BeoMaster 3400 FM station drift

yachadm — Mon, 28 Dec 2009 08:07:01 GMT

BINGO!!!!!

I went to my pile of old junk - I found a Philips carcass, and there was a ZTK22!!!!

I installed it, and it is reading 21.3V, but the problem is solved. All stations start up perfectly stabilized instantly, when the BM3400 is switched on.

I noticed something else very interesting:

Before, with the regular Zener 22V, if I adjusted the 26V poti to less than 25.2V, the FM station would start destabilizing.

Now, with the ZTK22, I adjusted the 26V poti down to 23V, and the FM station stays locked on.

Also, I noticed that at switch-on, the 26V rail is only 25.4V, and it takes about 2 minutes to stabilize at 26V. But this is unimportant operationally, because the ZTK takes care of the stability, and the FM remains stabilized.

Martin, do I understand you correctly that there are 2 types of Temperature-Compensated Zeners - ZTK at 500mW and ZD at 1.3W?

This is now a completed restoration - technically and cosmetically perfect! (But it did take a couple of years to get to this stage ;-)

Thanks to you all!!!!

Re: BeoMaster 3400 FM station drift

Die_Bogener — Mon, 28 Dec 2009 06:59:38 GMT

No, replacing a regular zener diode by a ZTK type makes no sense. ZTK diodes are really very hard to get, they are very rare and much more expensive. Lets say, 10 cent for a normal ZD22 is normal, but around 1.40-2.50 Euro for a ZTK type... that's relative.

I would use a ztk type if you still can get one. They are very rare meanwhile... i could not find one with 22V, only 6.8V and 33V.

And if not, use the 1.3W ZD type instead. The heat dissipation is better than the smaller 0.5W types.

http://www.reichelt.de/?;ACTION=3;LA=2;GROUP=A422;GROUPID=2994;ARTICLE=23076;START=0;SORT=artnr;OFFSET=16;SID=31k6BlsqwQAR8AAB4Y-E47c85120fb756d2e1df1411c00a7668ce

Re: BeoMaster 3400 FM station drift

yachadm — Mon, 28 Dec 2009 06:40:17 GMT

I was very afraid that you were going to say that - they are almost impossible to find!

At least now I know what ZTK means.

Is it worthwhile to use them instead of a regular zener?

Re: BeoMaster 3400 FM station drift

Die_Bogener — Mon, 28 Dec 2009 05:55:59 GMT

.........

5. I looked at D11 - it is located right next to the Oscillator can, below the 26V poti. In the SM, it is called a 22V regulator. The original was a ZTK22 (damaged and NLA), and I replaced it witha 22V Zener. It is measuring 21.6V.

........

A ZD22V zener diode is not a ZTK 22V diode.

ZTK= Zener Temperature kompensated

ZD= Zener Diode

Replace it with a ZTK type, these have a smaller temperature drift.

Re: BeoMaster 3400 FM station drift

yachadm — Mon, 28 Dec 2009 02:17:38 GMT

Hi Martin,

1. Do you remember that you introduced me to Wima about 4 years ago? Since then, every cap which is 4.7uF and below, I replace Wima MKS or MKP automatically. Wima has a large warehouse in Israel, and they sell at prices well below the rest of the world, so it is a very easy choice.

So, I already put these MKS2's at the beginning of the restoration, many years ago. See the picture.

(BTW, ALL resistors on PCB2 are also replaced by Vishay Dale CMF60 - I had to, because of the corrosion, but these are far more precise than the original carbon units)

2. TR2/TR3 replaced by matched BC550C Low noise - no improvement.

3. 0C3 also replaced by MKS2 now - no improvement.

4. I see an interesting phenomenon - I place my DMM probe at the 26V testpoint, and at switch-on, it is only 25.54V. It increases gradually, and after about 3 minutes, it stabilizes at 26.0V.

I always made my adjustments on any radio, after the radio has stabilized for about 10 minutes.

Perhaps I should adjust the 26V when cold, and then after stabilizing, it would be about 26.4V?

OR should it be 26V immediately at cold switch-on, and remain constant at 26V after warming up?

6. At IC CA1310, pin 2 is 3.7V, and according to the SM, it should be 3V. Adjusting L3 did not make a difference (I marked the point, but didn't like to adjust, because I remember that B&O specifies not to touch these coils).

Re: BeoMaster 3400 FM station drift

Die_Bogener — Sun, 27 Dec 2009 16:44:35 GMT

Yes, this is interesting. This would mean, that something around TR2/TR3/C16/C17 is wrong, the tuning frequency with 18,4V ist affected.

Did you use electrolyth caps or plastic caps?

Original they used in this time tantalum caps a lot. They are complete different to todays electrolyth caps. Tantalum is polarized, but is not in its function identical to electrolyth. I would replace tantalum only by MKS or MKP bipolar plastic types.

Tantalum will survive wrong polarity with little currents, it will not be destroyed. But electrolyth will be destroyed after some minutes. Wrong polarity will need a "repair time" for a electrolyth cap, a tantalum does not need this.

Replace C16/C17 by a Wima 0,47uF type.

Re: BeoMaster 3400 FM station drift

yachadm — Sun, 27 Dec 2009 14:22:47 GMT

If I remember correctly, it was a tantalum, with high ESR.

I put in a regular Panasonic EB 1uF 50V electrolytic - any other recommendations -
perhaps a low-ESR, or perhaps increase the uF being an electrolytic instead
of a tantalum?

I just noticed that if I engage the AFC immediately after switch-on, the frequency stabilizes immediately and perfectly, with no waiting time. Does this indicate where to look, to eliminate the remaining delay?

Re: BeoMaster 3400 FM station drift

Die_Bogener — Sun, 27 Dec 2009 13:35:29 GMT

What about the cap 1uF 0C3 ?

This one is a filter for the tuning frequncy?

Re: BeoMaster 3400 FM station drift

yachadm — Sun, 27 Dec 2009 13:08:24 GMT

OK, much better.

I don't have the original components - this was rescued from the skip about 7 years ago, with water damage and corrosion almost everywhere on all the component leads. It was a massive job to cleanup!

Anyway, the FM section got all new components, passives and semis. I cleaned out the coils as much as possible, and there was no apparent damage.

However, I have good stock of most components, and the 3rd 15V Zener I tried was exactly 15V.

There's now 14.34V, up from 13.8V, and it's now 10 seconds to full stability.

I replaced R45 off the IC and also D6 1N4148, but no further change in stability.

Menahem

Re: BeoMaster 3400 FM station drift

Die_Bogener — Sun, 27 Dec 2009 11:11:08 GMT

I would replace D5 for a better 15V zener diode, maybe temperature compensated. 13,8V or 14,3V makes a difference in FM units, since the frequency is adjusted with a voltage. A floating power supply will cause this problem.

D6 could be defect and blown, this could cause this raising voltage...

R45: Maybe you remember the BM7000 potis for the "no load current"? They never measured defect, but it was the reason why all the BM5500-7000 shut off suddenly. Exchange it and make a new adjustment.

Re: BeoMaster 3400 FM station drift

Dillen — Sun, 27 Dec 2009 10:46:01 GMT

Both voltages are important;
The 14,3V since it supplies the FM frontend.
The 26V since it supplies the AFC "balance" circuit.
The TR7 emitter I would have expected a little higher and I think that's where the main problem is.
If you still have the original TR7 and zener(s), I suggest you try to remount them and check again.

Martin

Re: BeoMaster 3400 FM station drift

yachadm — Sun, 27 Dec 2009 09:51:56 GMT

Martin and Martin - Thanks for your replies ;-)

I looked at the power supply, and changed C25 and C26 at the bridge - voltage is up to 31.8V from 29V (still not 35V, but I think that's our poor quality AC, even though I'm running it through a power conditioner).

Time to frequency stability is much improved - now about 30 seconds.

At R42, the (new) big 120ohm resistor, input is 26VDC (spot-on), but output - (at TR7 Collector) is not stable:

When I switch on, it's 17.8V, and it rises gradually.

At 18.0V, the FM frequency is nearly stable and listenable, but the L&R indicator lights are not equal yet.

At 18.3V, the indicator lights are equal.

(TR7 emitter is stable at 13.9V, right from switch-on).

I have replaced ALL the parts in the PS circuit - from TR7 to the right.

But (the new) D5 Zener 15V is showing 14.6V at the cathode - is that significant?

Martin Schmidt - re R45 Poti - do you mean R54 Crosstalk Poti?

Martin Olsen - resoldered all connections on oscillator PCB, tapped the metal cap housings, to see if any change - none...

Menahem