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beomaster 2000 indicator lights

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johndon
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johndon posted on Sat, Apr 22 2017 2:01 AM

Hi

I am new to this forum.I live in Brisbane Australia. I purchased my B&O system in 1975. It comprises a Beomaster 2000 ( 2801), Beogram 4002 and a pair of M70 speakers. I did have a Beocord 2000 but it died a long time ago. The amplifier was working OK but the heatsinks were getting really hot. Thanks to this site, I found how to cure the overheating. I still have one problem. None of the indicator lights work. The individual bulbs are all ok. I have desoldered them, checked continuity across the terminals of each bulb and resoldered them back on to the board  (4)

The unit is on the workbench and I have tested the input voltage into board 4 and it's OK but the bulbs still don't light up. Can anyone give me some ideas of where the problem might be. I am NOT an electronics technician however my late father was so I have picked up a bit of knowledge from him. I have downloaded the service manual and I can sort of follow a circuit diagram and use a multimeter.

 

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johndon
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Answered (Verified) johndon replied on Sat, Apr 22 2017 10:08 PM
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Hi Martin

 Thanks for the info. I'll let you know the result.

I do have another small problem. I changed the 2 trimpots on board 7 to fix the overheating problem. When I installed the new ones, I wound the trimpots to zero and then brought them up slowly until I got the correct value reading on R117 and R217 as per the service manual. However the next time I checked, the left channel ( R117) reads exactly 10mv but the right one ( R217) fluctuates wildly up and down. The cooling fins stay cold.   Any ideas?

regards

 

John

Menahem Yachad
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Verified by johndon

You changed the Zener Diode?

Do you mean the Tuning Voltage 22V Zener?

If so, you cannot use a standard zener.

You must use a Temperature Compensated Zener, otherwise the stations will fluctuate all over the dial, and you'll have the problem of no stereo.

Anyway, if you still have the original zener, then reinstall it, or look for a ZTK22, originally made by Telefunken or Siemens, now Vishay.

Menahem

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Menahem Yachad
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Big mistake of newbies is to replace semiconductors willy-nilly, without ever having checked them.

I suggest that you replace NO transistors here, until you have confirmed with ABSOLUTE certainty that they are defective.

If you replace a transistor with the same model, but a different hFe gain grade, you can induce oscillation, and cause catastrophic failure where none would have occurred before.

Enthusiasm is fine, but uneducated enthusiasm is deadly.

You really need to know what you're doing, before changing transistors.

 

I do not see where in any BeoMaster 2000, that you need 4 MPSA06's.

There are only 2 of these NPN's installed in the machine.

The other 2 MPS's are PNP's, and if you replace NPN's into the place of a PNP, you can sell tickets for a nice light and sound show.

So, I'd advise you just to hold off laying out money right now, except for a Transistor and hFe checker.

Dillen
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Great idea to make sure, you know what you are talking about.
Beomaster 2000 was made in two different versions (Both are Type 2801).
The amplifier module was revised from serial number 143001.

Martin

johndon
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Hi Martin & Menahem

The serial number of mine is much higher. When I test the transistors, is it OK to leave them soldered onto the board or will the meter pick up from something else in the circuit?

 I now have hook leads for my multimeter.

John

Dillen
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The meter just sends out and receives.
It cannot see what it is measuring into or onto - and neither can you if you leave other components connected to the device undergoing tests.

Martin

Menahem Yachad
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As a general rule, all components must be removed completely from the PCB, in order to test them.

The rare exception (and even that is not always correct), is testing a capacitor for ESR.

You need a special ESR Tester for that.

If you want quality equipment for hobbyist purposes, check out Peak Electronics.

Their Capacitor tester is the ESR70

Their SemiConductor Tester is the DCA75

johndon
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Well thanks to Martin and Menahem plus a local electronics workshop the Beomaster is now working again. One of the mechanical problems was in the dial cord mechanism where the left side pulley pillar had broken. It had been repaired in the past using epoxy adhesive. The tension of the dial cord places a fair amount of pressure on the pillar, hence the break. Knowing that I couldn't get a new one, I decided the make a new pulley mount. I cut the old one and the left hand mount on the dial panel off using a circular saw on a dremel. I then made a new mount using 3mm, 5 ply aircraft ply and a small block of Australian hardwood to mount the pulley on. I had a 2/56 thread tap which just happened to be the right diameter and pitch for the screw of the pulley. After cutting the thread I reinforced it with some thin cyanoacrylate adhesive wicked into the hole. I was then able to fit the screw firmly into the timber. In the photo, you can see the epoxy adhesive gluing the plywood to  the plastic. I used some cotton flocks ( used as a fibreglass resin filler) to reinforce the epoxy.  Before I refitted the mount to the chassis, I cleaned the steel shaft with 0000 grade steel wool and a thin lubricant called Tri Flow ( used by bicycle mechanics) I then wiped it clean with paper towel and cleaned the plastic guide for the tuner arm with a cotton bud dipped in Shellite.( my late father always told me that Shellite--- which is pure hydrocarbon-- doesn't leave a residue of itself)  It had a layer of black gunk inside. A couple of drops of Tri Flow on the shaft and the tuner arm slipped freely along the full length. I then reassembled everything using the guide in the service manual to re thread the cord. I might add it is not an easy job to get right. The tuner arm lamp had burnt  the inside of the plastic over the years so I used a timber drill bit ( without tapered flutes) to clean the hole and then glued the new globe in place with clear neutral cure silicone.

Now when I spin the dial disc, the arm moves freely up and down the shaft, the tuning lights work, the stereo light works and I have an operational tuner again      


Menahem Yachad
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Well done!

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