No need to be like this please. i misread the SM as L1 does need 30Ma. I fitted 80mA lamps and there is no change. Instead of shouting at me EXPLAIN why the lamps are so important. Nobody will learn anything like this, ok?

I checked all transistors again. I reflowed more joints and the voltages are steady now (more or less) instead of falling / rising. TR7 reads (FM input, stereo signal):

B = 14,85
C = 8,30
E = 7,51

I can check IC1, no problem

Bert

IC1

B = 14,71
C = 9,28
E = 14,85

Values holding steady,

Bert

I believe I found the culprit but need to check this further. C14 at 2.2uF was changed into a film capacitor. I replaced this on a hunch to a polarised electrolytic. It appears the audio is back now. But let it play for some time to see if this really works.

Sometimes you need to have a polarised cap in the circuit.

Bert

Yes you are basically shouting at me in the manner you write.  I appreciate your help but please try to explain why you need someone to do 'something'.

I readily will tell when I make mistakes because that is part of the whole gig: we make mistakes. We all want to learn. And your knowledge on this machine is rather larger than mine.

Bert

 

Hi Bert,

Seriously how do you perceive Martin as being aggressive?

He’s one of the kindest and helpful people I have known since I registered here in 2009!

What he offers are just instructions and also some useful teaching. Does he really have to put a ‘please’ before every helpful instruction?

Jacques

Aggressive? Did I say that? I perceive that message as directive and pedantive towards me. I do not know this person nor do I perceive such messages as 'learning' but rather as pushing down on me.

Nobody will learn anything without any other explanation than 'just look in the schema buddy'. I spent the better part of an hour removing two buried lamps, having to resolder wires, for what? I can see their position but the schema tells just a tiny bit of a larger story, a story that isn't shared.

I honestly appreciate any help from any one person. But this kind of approach is just not in my ballpark.

Apologies from me if that message was not meant like that, of course.

Bert

 

 

 

 

For the record, what actually happened. I serviced this machine some time ago. All small value capacitors were changed into film. Last week I found that I missed 2 caps hidden below a cable truss. These were 4.7uF (C13) and 2.2uF (C14).

Without thinking I changed C14 to a 2.2uF film cap. And then when I tried the machine the audio would drop off after some time. On a gradual slope. So an odd situation.

With thanks from Glitch it was deduced that the muting circuit was indeed the culprit. It dawned on me after some time that this was exactly where I changed the 2 caps. I know, it is really that stupid and obvious.

The circuit cannot operate with a non polarised cap in this position. Changing that capacitor into a polarised electrolytic made the circuit work again. Audio has been playing for 3 hours now without a hitch.

So lesson learned: always double-check the schematics before changing a polarised into a non-polarised capacitor.

Many thanks again to everyone who chimed in with their thoughts, much appreciated!

Bert

 

Actually, Craig suggested that the issue lie in the mute circuit. I merely made a suggestion of how to prove or disprove his supposition. Also, if the problem wasn't self-inflicted, the debug path that Martin was trying to lead you down WOULD have led you to the solution.

BTW, the issue was likely more related to the ESR of the capacitor than it being polarized.

Glitch

I always steer clear of choosing different types of components and stick to what there was in the first place. For instance, no metal oxyde resistors if there were carbon ones, no film caps instead of electrolytics.

No surprises.

I restore things. I don’t claim to be able to upgrade them. I am not. If there was a TL072 then I’ll replace with a TL072, not a fancy audiophile op-amp that I know will bring nothing, or perhaps just trouble.

So whenever I restore a B&O device it will always be like for like.