Dillen wrote:

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

Martin 

Confirmed : Single pin side of trimmer is connected to BC154 base and I get continuity. 

Confirmed : Emitter resistor is OK

Thanks,  Anton

manfy wrote:

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.

I understand that the cathode side of a diode is indicated by a thin band around the end of the diode diode. Just to make sure there is no evil conspiracy and mine work the other way round i tested an unused one. Red lead on red side and black lead on side with band ie negative ie cathode gives me 0.624V. Reversed it gives 0V.

manfy wrote:

- check connections as suggested by Martin above

Done, all is as it should be

manfy wrote:

- check if cathode of zener is connected to emitter of BC154 -> if not, zener is mounted with wrong polarity!!

Tested in diode mode negative lead to cathode - 0.553V, in reverse I get 0.583 - that looks a bit wrong?

I next tested resistance which slowly just kept on climbing higher and higher - i got bored when it got to to over 40k.

This is also a bit odd - noted that the 1.2K resistor at #903 is excessively hot (like ouch hot), on the BC141 emitter side its reading +-42V and on the other side its 7mv and that is supposed to be 9V, probably explains why the radio circuit is currently dead.

Hi Anton,

AntonvZ wrote:

I understand that the cathode side of a diode is indicated by a thin band around the end of the diode diode. Just to make sure there is no evil conspiracy and mine work the other way round i tested an unused one. Red lead on red side and black lead on side with band ie negative ie cathode gives me 0.624V. Reversed it gives 0V.

Yes, that's the right way to test. So the zener diode seems OK.

AntonvZ wrote:

Tested in diode mode negative lead to cathode - 0.553V, in reverse I get 0.583 - that looks a bit wrong?

I don't understand. You tested the connection from zener cathode to BC154 emitter in diode mode? If so, it suggests that the zener diode is really mounted the wrong way. The odd value upon reversal of test probes could happen because of the in-circuit test. The measurement current finds its own way across other components. It's best to use resistance measurement for checking direct connections.

AntonvZ wrote:

I next tested resistance which slowly just kept on climbing higher and higher - i got bored when it got to to over 40k.

Now that is really odd and wrong. You should read zero Ohms between zener cathode and emitter of BC154.
What is the reading between zener anode and the BC154 emitter?

AntonvZ wrote:

This is also a bit odd - noted that the 1.2K resistor at #903 is excessively hot (like ouch hot), .

I'd say that's alright. You're running the unit now on 40V instead of proper regulated 30V. Resistor 903 and Zener 904 are the 9V power supply for the tuner. At 30V the resistor would run at 0.3W, but with the excess voltage it runs at 0.8W. Since it's probably just a 0.5 Watt resistor it might burn up if you run the Beomaster for too long.

As long as the 30V issue is not fixed, you should turn on the unit only for a short time for testing! The excess voltage can cause all sorts of problems and even damages.

Oops, sorry. Now I get it.
First you tested an unused diode and that one seems to be ok. Then you tested the Zener in-circuit and you get 0.6V in forward and reverse direction.

Since the resistance test between zener cathode and emitter is wrong, we can be sure that there's something wrong with this zener. Remove it and test it outside the circuit. If damaged, mount a new one and pay attention to polarity. The cathode must be connected to BC154 emitter as you see in the circuit diagram.

rgds, manfy

linkI ran a quick simulation on LTspice earlier and it seems if only the zener diode is mounted wrongly, you would get quite different voltage readings. However, if the collector-emitter section of BC154 is shorted out, the voltages I get look very similar to what you posted earlier.

You should probably do a diode check on BC154. That's quite easy since a transistor acts like 2 diodes (for testing purposes):

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So, if you get anything but OL/OR (overload/over range) in diode test/resistance mode between emitter and collector, you need to change the BC154.
You should still make sure that the zener is mounted with correct polarity, though. It's equally important.

rgds, manfy

Hi Manfy

Checked again, diode cathode is connected to BC154 emitter. It is in the right way.

BC154 on diode check , circuit off and unplugged I’m sometimes getting OL and sometimes 0.001V between emitter and collector.  There is resistance of 4.3 0hm. At 0.001V does this mean the transistor is shot or is this just from being in circuit?

B-E and B-C I get 0.843V and 0.871V respectively with 5.25 K ohm resistance on both paths. 

Best regards as always

Anton

AntonvZ wrote:

BC154 on diode check , circuit off and unplugged I’m sometimes getting OL and sometimes 0.001V between emitter and collector.  There is resistance of 4.3 0hm. At 0.001V does this mean the transistor is shot or is this just from being in circuit?

Hmm...I can't guarantee that the transistor is shot, but it's sufficiently strange to investigate further.

The 4.3 Ohm between C and E is way too low. In-circuit test can show strange values because of secondary circuit paths, e.g. when measuring C-E in diode check, you'll slowly charge up the 3000uF capacitor, which results in unstable measurement and as soon as you reverse the test probes you might see odd values caused by this voltage from the cap. Also, when you're connecting the red probe to the collector of BC154 and the black lead to the emitter, you should actually read 1.2 to 1.5V because you're effectively measuring the B-C path on BC141 in series with the zener diode in forward direction.

Anyway, we know for sure that something is wrong in the power supply and BC154 is currently your best bet. Here's what I would do now:

1) Unsolder BC154 and do a full diode test (in forward and reverse direction)

2) Now with BC154 removed, we have a good chance to get more consistent values in an in-circuit test of the remaining components:

2.0) First I'd double-check visually the proper connection of BC141 and 2N3055 (since you replaced those previously and it's just too easy to mix up B-C-E when you're in a hurry)
2.1) Measure BC154 C-E path on the PCB. If you still get low Ohm values, there might be a solder blob or something that short-circuits that path
2.2) Do a diode check on the zener diode. You should read 0.6V in forward direction and OL in reverse.
2.3) Do a full diode check on BC 141 again
2.4) If there are odd measurements on BC141, I might even unsolder the wires to the 2N3055 and recheck the BC141. At the same time I'd diode check the 2N3055

3) If all these checks are good and show no sign of component damage, I'd simply assume that BC154 is damaged in some way. The diode test on transistors is very rudimentary and does not guarantee that a transistor is good! In 10-20% of the cases the transistor might have some problem that cannot be measured with a simple diode check.

3.1) If you don't have a BC154, the replacement model is BC416 (so says the internet). If you can't find BC416, you might try the BC161. BC161 should work fine for this purpose and since you fixed your preamp with that model you might even have some spare 161's available.

Good luck with testing! 🙂

manfy

manfy wrote:

If you don't have a BC154, the replacement model is BC416 (so says the internet). If you can't find BC416, you might try the BC161. BC161 should work fine for this purpose and since you fixed your preamp with that model you might even have some spare 161's available.

I know from previous inquiries that BC154 and BC416 are not available locally. So last night did some digging on Google and found transistor BC214 which is very similar to to BC154 and picked up a few on the way to work. See below.

So the plan is to just redo that whole part of the board, replace zener, replace BC141 (again) replace BC154 and while doing that check the wiring from 2N3055, dont want to desolder that just yet because the little plastic bushes are not going to survive a 3rd desolder and resolder.

Will test everything before it goes in and of course I will pay particular attention to everything going in the right way and then do the tests in your previous post.

Thanks for all the help thus far 🙂

Recently also came into a Beogram 1001 (stylus missing diamond and needs belt replaced) , Beomaster 1001 (works, kinda), Beocord 2200 (DOA), and Beovox 2705 (both bass drivers foam shot and one with a seized voice coil) Looks like i'm going to be here for a while 🤔

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Beovox 2705?
Sure they are not 2702?

Martin

Dillen wrote:

Beovox 2705?
Sure they are not 2702?

2705 for sure, will put up the sticker later, 25w RMS 45w peak.

Exactly the same size and grill type as my Beovox 1200's, just in teak and not rosewood.

Quite excited to hear (once I get them sorted) to hear what B&O ambionic sounds like, using the 15w 1200's for the sides.

Regards

Anton