So now for the next set of issues.

1. Stable voltage is now sitting at 40.8V iso 30V. Adjusting the trimmer has no effect whatsover and this is a new one.

2. My original problem. The RIGHT preamp channel (QII) is dead.

• electrolytics caps in that area have now been replaced
• it is not the cable (2 RCA to DIN) as it works fine with two other audio sources
• it is not the turntable either as that works well with my Technics amp
• tape and QI work fine with other audio sources, the dead right channel is only on QII.
• the pins on the QII din input are configured correctly 
• there is continuity from the pins to the PCB
• there is 0.65V power supply to both 10u/64V caps
• doing left to right voltage voltage checks are giving approximately the same values left to right.

Anyone else every had this problem?

Thanks in advance.

Anton.

Very well done!

craig

Dillen wrote:

Points to a problem with one of the output stage transistors or, perhaps most likely, one of the driver transistors.

Hi Martin

Still having a problem with getting 30V stable. Adjusting trimmer has no effect.

Done the following measurements and cant figure out where exactly the problem is.

Power filter capacitor 43.8V

Power transistor 2N5034-  Base red wire 39.8V, collector (think brown wire) 42.6V, emitter (think orange wire) 42.98V - as far as I can read the circuit diagram i should be getting 30V on the emitter.

Rectifier - orange wire 43V, brown wire 1 20.7V, brown wire wire 2 20.05V, 4th pin assume ground 15mV 

400u/40V capacitor - 40.02V

Stereo bulb 39V going in 9V coming out.

Point J/K 39.9V

Is this the 2N5034 power transistor causing the above, if so can i replace with 2N3055 (which i have) as it seems as if it was used on some models as per below snippet from B&O repair manual.

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"Power transistor 2N5034-  Base red wire 39.8V, collector (think brown wire) 42.6V, emitter (think orange wire) 42.98V"
- It's an NPN transistor. With the base voltage lower than the emitter, this transistor should be closed.

" as far as I can read the circuit diagram i should be getting 30V on the emitter.""
- No, You should have 30V on the collector. Make sure you get the pins right and measure the right place.
But in this case it looks wrong any way around, so I suggest you replace the 2N5034
You can use a 2N3055 if you don't have a 2N5034 (

Dillen wrote:

You can use a 2N3055 if you don't have a 2N5034 .

You will have to adjust the voltage regardless.

Hi Martin

Thanks as always.

Swopped out the 2N5034 with a 2N3055.

Update and Edit, just to set the record straight. My Beomaster 1000 version 2318 came with 2N3055 transistors and not 2N5034 as indicated in the circuit diagram supplied with the set. I only noticed this weekend while cleaning up that the one I had removed was in fact a 2N3055. 

Readings now 43V on the emitter, 39.4V on the collector and 43.6V on the base.

Still can't adjust voltage at trimmer.

Will next look at the BC154 and the zener diodes.

Dillen wrote:

"Stereo bulb 39V going in 9V coming out."
- With 30V across a 18-19V lamp, it must be lighting up the whole village?

Indeed, a whole new feature, the way it brightens and dims depending on the volume setting is escpecially entertaining. 😕

Regards

Anton

AntonvZ wrote:

Dillen wrote:

"Stereo bulb 39V going in 9V coming out."
- With 30V across a 18-19V lamp, it must be lighting up the whole village?

Indeed, a whole new feature, the way it brightens and dims depending on the volume setting is escpecially entertaining. 😕

That is a good sign that your 2N5034 (now 2N3055) doesn't regulate at all. The volume setting changes the current drawn and the 30V supply goes down accordingly.

Check the Zener diode 908. You should normally read 21V on the cathode - in your case it should be 30.4V since you get 39.4V on the collector of 2N3055. If the diode is ok, check transistor BC154 and if that one is ok check the BC140.

Beyond that, there's nothing in that circuit that gets easily damaged.

Rgds,

manfy

manfy wrote:

Check the Zener diode 908. You should normally read 21V on the cathode - in your case it should be 30.4V since you get 39.4V on the collector of 2N3055. If the diode is ok, check transistor BC154 and if that one is ok check the BC140.

Hi Manfy

This is the most frustrating thing ever. 

Cathode of Zener diode 908 reads 40.6V (I have already replaced this with a 9.1V zener diode)

BC154 C=41.2V E=41.2V B=39.2v

BC140 C=41.5V E=41.5V B=40.8V (I have already replaced this with a BC141 transistor, closest match)

Trimmer Leg connecting to 470 ohm resistor #905 =39V, Leg connecting to 2.2K ohm reads 15.64V. Single leg side reads 39.2V and adjusts to 15.64V if you turn it.

My experience with electronics limited, would appreciate you thoughts on the above.

Regards

Anton

Is the trimmer slider ("single pin side") connected to the BC154 base at all?
Is the emitter resistor (910 / 3,3K) OK?

Martin 

AntonvZ wrote:

Cathode of Zener diode 908 reads 40.6V (I have already replaced this with a 9.1V zener diode)

BC154 C=41.2V E=41.2V B=39.2v

BC140 C=41.5V E=41.5V B=40.8V (I have already replaced this with a BC141 transistor, closest match)

Trimmer Leg connecting to 470 ohm resistor #905 =39V, Leg connecting to 2.2K ohm reads 15.64V. Single leg side reads 39.2V and adjusts to 15.64V if you turn it.

Thanks! That's helpful.
At first look, I'd say you mounted the new zener the wrong way around, i.e. in forward direction. 😠 No worries, it's no biggy. The 3.3k resistor in series should limit the current to just 13mA, which shouldn't be a problem for the diode.

First checks (with power cord disconnected); multimeter set for continuity check:
- check connections as suggested by Martin above
- check if cathode of zener is connected to emitter of BC154 -> if not, zener is mounted with wrong polarity!!
- check zener with multimeter in diode test or resistance test mode in forward AND reverse direction.It could be dead (=shortened out) and if so replace it!

BC141 voltages look good, except collector voltage, which should be 30V regulated; but that's ok for now.
Trimmer voltages look good, i.e. trimmer is working. Set output voltage of trimmer to approx 21.5V (that's the nominal value that should give you roughly 30V once the power supply circuit is fixed).

More later.

rgds, manfy.

linkJust to make sure we're talking about the very same thing:

You have a BM1000 type 2318. Martin said that it uses the same board and design as 2317. So, I copied the power supply from my 2317 service manual and added the nominal voltages in blue. All my posts and suggestions are based on this specific circuitry below.

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Some important notes about the voltages given:

- the ground symbol (which normally represents 0V and often connected to the chassis) is positive in this design!!
- if you connect the black probe of your multimeter to the chassis and measure the voltages with the red probe, you will actually get negatve values on your multimeter!
- the voltages given are measurement values referenced to positive ground (= red probe of multimeter connected to chassis, black probe connected to test point)

Do NOT forget about this! It's an important fact for:
- polarity of electrolytic capacitors, diodes, transistors
- differential voltages measured directly between transistor terminals
- calculations made for the purpose of assessing behaviour of the circuit or individual branches in it
- and probably some other things I can't think of right now...

[edit: reworded and reformatted for clarity]