Hi all,

I've just been working on a BG6000 with the AC motor.

I may be wrong, but this machine definitely appears to be hot, after playing an LP.

The aluminium base at the left front corner is HOT.

Now, I took out the motor, a Sonceboz 1112 - made in Switzerland, with the hope of opening it up to clean and relubricate, but I couldn't find any way to open it, or to disconnect the blue wiring harness.

I contacted Sonceboz, and apart from warning me that if I opened it, I would damage it, did not provide any help, and suggested that I contact B&O.

Can anyone offer any pointers here?

Is it normal for it to heat up like this?

Should I be looking at replacing the 2N3055 control transistor? - it does check OK, with the diode check.

Regards

Menahem 

Hi Menahem:

My BG4002 runs "warm" but not scorching hot. It usually takes more than a few LPs for the temp to rise though.

Is the 2N3055 outputting the right voltage? If it is running too hot there must be excessive current draw. The only other device that draws lots of current is the solenoid. Check to see if it is hot! Those things can burn up in certain faults.

Derek 

 

Hi Derek,

My Collector and Emitter voltages are pretty close to the numbers in the Service Manual.

The Base voltage is not shown in the Service Manual.

Could you measure the voltages off your 2N3055, and I'll compare them to mine?  

Thanks

Menahem

The front corner in my BG6000 (AC) gets pretty hot (rather than "warm") as well. I thought the heating might just be normal. The motor itself rotates quite effortlessly by hand, so I don't suppose it has a problem.

I have measured all voltages in the circuit as shown on Service Manual page 3-5.

All voltages leading to the motor are spot-on:

0TR2 and 0TR3 Emitters are 11.36VDC (11.4V required);

0TR2 Collector is 22.7VDC (22.8V required).

The only possible discrepancy I can see is the AC Voltage across the motor - either side of the 150uF Bipolar, is showing 8.2VAC. The Service Manual shows 5V +/- 0.5V (or maybe I misunderstand the reference).

I measured it at 8.2VAC both unloaded, and then loaded with the belt and platter turning.

I then replaced the new Capacitor with the original ancient B&O 150uF Bipolar (actually 174uF), and got 8.3VAC.

So I'm not sure that I understand the discrepancy between the 8.2VAC, and the 5V shown in the manual.

Any ideas from the more experienced here?

Menahem

I did some measurements on mine, too. All are without load, since it was hard to get around with the platter on...

Across the motor cap, I have 8.8 VAC. I'd expect this be high due to increased ESR of the original cap? I didn't bother replacing it, since I've heard it seldom fails, and its value is not critical to operation.

Anyway, I think the heat doesn't come from the motor or its drivers, but from TR1 which is installed beside it. I believe you have 230 VAC network nowadays as well? The Beogram only has settings for 110/130/220/240. Mine is set to 220V. Therefore, the voltage after the rectifier should be about 5% higher than specified, and so will be the power dissipated by TR1.

True enough, I measure 45/38/34 volts on the collector (case) of TR1 in off / on / arm down, instead of 41/35/31V as specified in the service manual. I don't know the current through TR1, but I'd expect it to dissipate several watts more than "normal". Perhaps switching the Beogram to 240VAC would cool it down? Alternatively it might not get clean power after the regulator anymore...

Hi Mika,

Always such a pleasure hearing from you!

Actually, our line voltage varies from 227VAC to 237VAC, so I set all my electronics to 240V, where possible.

So, it is still running hot with the selector even set at 240V.

You seem to be pretty locked on the idea that 0TR1 is the cause of the heat dissipation, and the BG6000 casing is a giant heatsink.

I've checked the C-B and E-B forward voltages, and they check out OK.  

If all the line voltages are OK, how would I be able to tell if 0TR1 is, in fact, faulty? Other than getting a new one and wiring it in, then waiting to see if it gets as hot?

Menahem

yachadm:

You seem to be pretty locked on the idea that 0TR1 is the cause of the heat dissipation, and the BG6000 casing is a giant heatsink.

Well, it was just an idea. Since it was pretty easy to desolder the wire from the supply caps to the collector of 0TR1, I put a multimeter in series and measured the current. I have 0.48 amps with the motor running and arm up, and 0.52 amps with the arm down. Since the voltage drop across TR1 is 15 and 11 volts respectively in my case, that would mean 6-7 watts of heat will be generated in TR1. I'd expect it to be quite warm! It gets warm to the touch after a couple of minutes of running, while the motor itself is still cool.

I don't think the transistor in this application can fail so that it heats more than normal, it'll either work or not.

Don't know if this helps, but if you have similar current consumption, at least both of our decks are the same