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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Anyway, if you still have the original zener, then reinstall it, or look for a ZTK22, originally made by Telefunken or Siemens, now Vishay.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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Dillen
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Dillen replied on Sat, Apr 22 2017 7:20 AM

Have you checked the lamp in the dial pointer?
The ON and STEREO lamps will not work without a good dial pointer lamp as they are in series.
The tuning discriminator lights will only be lit when tuned near a strong station (good antenna).

Still no light? Check the zener and the ground connection..

Martin

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

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

johndon
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Hi Martin

Thanks to your help, I am getting there. I found some LED globes of the correct value and now the dial indicator light and the ON light are going. Does the stereo light only come on when the tuner is locked in to a stereo FM station. It's so long since it worked, I can't remember. I also changed the zener diode.

On my previous post I said that the idle current readings were on R117 and R217. That was incorrect. I took the readings on R119 and R219 after the trimpots were changed. It almost needs a second pair of hands to adjust the trimpots while holding the probes from the meter on the resistor.

I am close to getting the unit off my workbench and back where it belongs.

Also one other thing. My M70 trumpet stands have gone a dull grey. Do you know if re-anodising will help to restore the soft shine or is it easier to paint them silver?

 

regards

 

John

Dillen
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Dillen replied on Wed, Apr 26 2017 8:08 AM

LED globes of the correct values? There's no such thing.
LEDs will not work for the discriminator lights, - they are current-controlled.
I suggest you fit correct filament lamps.

LEDs won't look right anyway.

Yes, the stereo indicator should only light up when a (strong) stereo station is tuned.

Get some probes with hooks. Holding and balancing pointy probes is asking for trouble. It takes no more than a slight slip to short
something and cause havoc.

Martin

johndon
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johndon replied on Wed, Apr 26 2017 11:46 AM

Hi Martin

Thanks for the advice. I'll change the globes for the balance lights back to filament. I couldn't find any globes the correct value that's why I went for the LED's. After I posted my previous note, I found the original owners handbook for the Beomaster and sure enough it says that the stereo light only comes on with a stereo FM signal.

I'll buy some hook probes as well.

With regard to the M70 trumpet stands, I think the easiest way to restore the colour is to paint them with light silver 2 pack car paint. I don't think the original finish was anodised anyway.

Thanks again. You've been a great help.

 

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

johndon
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Hi Menahem

 Yes I did change it. I haven't reconnected anything yet and yes, I still have the old zener. Thanks for the tip. I'll re-install it. I'll let you know the result later today as I am about to finally reconnect

 

regards

 

John

johndon
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Hi Martin and Menahem

 The indicator and tuning lights are now all working properly again. When I connected the system up again, as I turned the power on, there was a crackle and pop from the right speaker but I can't get any sound. I've swapped the speaker leads and the speaker and it's leads are fine because the right speaker works when plugged into the left channel.

The cooling fins on the left side are just warm but the right side are stone cold. I set the idle current to exactly 10mv on each channel as per the manual but I think there must be something else gone on the right side. Any tips on where to start looking?

regards

 

John

Menahem Yachad
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I've seen that problem, and IIRC, it was a MPS-type transistor, which is one of the driver transistors.

This info is from my memory, so I'm not guaranteeing anything.

Of course, do a visual check, to determine whether any transistors show signs of trauma.

And check all non-trauma'd transistors in the failed output amplifier for correct hFe.

1. Build yourself a DimBulbTester (DBT) - google it.

2. Always connect any Device After Repair via a DBT, until you have established that it is working perfectly.

3. After switching on again, you'll need to recalibrate the Bias Voltage - you did replace the Bias Potentiometers, didn't you?

johndon
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Hi Menahem

Thanks for the tip. I'll make a dim bulb tester today. When you say Bias potentiometer are you referring to the two trimpots on board 7 ( 7R117 and & 7R217) ? If so, the answer is yes I have replaced them both. I quickly discovered that they need to be wound down to zero and then brought up to voltage slowly.

 Is the driver transistor the big one secured to the heatsinks? Sorry for all the questions but I'm not an electronics technician. I should have paid more attention to my father when he tried to explain electronic components to me!!

 I'll keep you posted on my progress. After the success with the indicator lights, I'm keen to keep going.

regards

 

John

Menahem Yachad
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On the schematic which I have, the 2 Bias potis are shown as 7R118 and 7R218, 250 ohms.

Of course there are always undocumented changes, so your's may have a different label, or you may be reading the label wrong.

The big transistors are the OUTPUT transistors - TIP141 and TIP146.

The DRIVER transistors are smaller transistors on the PCB.

TR105/205 is MPSH54 or MPSH55 PNP

TR109/209 is MPSA06 NPN

TR109 comes off the constant current generator, so I'd be inclined to check that one first.

johndon
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Hi Menahem

 I think we may not be reading from the same circuit diagram. My unit is a type 2801 I have changed the two trimpots ( R117 and R217) and reset the no signal current as per the manual. I now have the 2000 back on the bench and I think that the darlington transistor 202 (TIP 146) may be faulty. The fuse 201 appears to be blown even though I can see the wire element. When I test it for continuity, the meter shows nothing and no sound

I can't find a TR109/209. The TR107/207 is an MPS A06

 Any way my local electronics shop doesn't have the correct darlington transistors so I have ordered them online from a supplier in Sydney so it will be a few days until they arrive. When I replace them, is it necessary to use thermal paste when screwing them on to the heatsink?

 In the meantime, I will get some fuses to match F101/201. Do you know if they are slow blow? it just says 1.6AT on the fuse.  On a previous post, you mentioned visually inspecting the transistors. What should I look for?

 Thanks to the help I am getting from you and Martin, I am quite enjoying the challenge of getting the system going again

John

Menahem Yachad
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John

You're on the right track.

 

Yes, my Schematic is for a Type 2801.

So, look for the 2 MPS transistors in each channel (Total 4), it's not important what the Schematic numbers are.

 

Always apply new paste, and pay attention to the mica insulators between the transistor and heatsink.

I hope you get the genuine transistors, and not counterfeits.

 

Look for burn damage or cracks.

Even if no obvious damage, that does NOT mean that they are OK.

The system has suffered trauma, and the damage may be invisible to the naked eye.

Google - how to check transistors.

You should also have an hFe checker, which checks whether a transistor's gain is still within the manufacturer's specification, shown on the datasheet.

 

1.6AT - T means Trage in German; Trage means SlowBlow.

 

You should NEVER blow any fuses, if you connect via a DBT.

The DBT lights up, instead of blowing a fuse.

johndon
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Hi Menahem

 I'll google the transistor check plus when I go to my local electronics store I will get 4 new MPS A06 transistors. I have located 207 and 208 on the board. The legs of 207 are quite bent so it may well have suffered damage.

 I am also going to make a DBT. One of my soldering irons is a battery powered IsoTip with a fine needle point and it works really well when soldering a new component onto the circuit board.

 I'll keep you posted with the progress.

 

John

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