Good work, and good pictures! Thanks for taking the time to post them.

Seems like your Beomaster has had a pretty good life. Mine have surface rust on the metal parts of the connectors, screws and on the chassis, probably from years in the attic or something. Especially the oldest which is a S290 as well, only 1390 serial numbers away from yours 😕

Thanks Mika,

yes, for it's age it's pretty pristine, just old but no structural deterioration, not one bit of rust. Same for the speaker elements, not the smallest hole. Except for the fuse holders that i changed before anything else, it was just a question of lubricating and fixing the component problems. It would indeed look like it has spent it's life indoors in the dry, like it sure deserves.

It's pretty amazing actually that you own another that is as close a cousin of my one 🤒  Here's to them  

Sebastian

Well, I don't see any substandard work - looks like you did a good job!

Check those carbon resistors which are in the Power supply circuit, especially those whose function is to drop voltage - you'll probably find a couple out of spec.

Did you do a voltage check across the power cap, as before?

I'd be interested to see the difference in measurement results.

You're very lucky that the structure is in such good condition without corrosion.

Enjoy it for many years to come!

Menahem

Nice job, I agree.
Worth checking the 1,5Kohm resistor that sits right next to the cap with the severed pin on the stereo decoder.
It looks chipped but may still be OK.

Martin

yachadm wrote:

Check those carbon resistors which are in the Power supply circuit, especially those whose function is to drop voltage - you'll probably find a couple out of spec.

Did you do a voltage check across the power cap, as before?

I'd be interested to see the difference in measurement results.

Well, in fact they all seem to be just a bit above the supposed values, or close enough, so nothing to report really.

As for the power cap, no real change in values, i just noticed that depending on the input voltage it's more or less close to specs (normal, i suppose). So at 220V it's 34,5V, and at 240V it's 32V. Given that 34V is aimed at, i guess that operating it at 220V it is, then.

Dillen wrote:

Worth checking the 1,5Kohm resistor that sits right next to the cap with the severed pin on the stereo decoder.

It looks chipped but may still be OK.

It measures 1.55K, so seems ok as well. Looks like these dinosaurs of resistors do resist to time too.

So far, after the recapping and a few measures at same points around the power supply, things seem just a tad more balanced. I managed to adjust to a spot where i get around 24V/34V where needed, but the same problem than before remains at below voltages. This is to say that i have 34,6V on the power cap, it goes to 24V & 24,2V after the 2N555, from there it goes to the AC128 (24,2V / 24,4V / 34,6V), and it's after that, at AC126 that it goes a bit weird, and i don't know what it means ; i get 24,4V / 8,6V / 8,7V where i should have 24,4V / 9V / 9,4V ?

To the same effect, the amp board gets exactly 24V at arrival, but for example at the first input transistors i measure 7,9V / 8V / 16,5V where it should be 6,8V / 6,9V / 18,5V. And so it goes, everything below 24V is a little off.

Any idea what is to be looked for ?

[EDIT] I also get a somewhat high "bzzzzz" from the transformer which was already there from the beginning, but maybe just a bit louder now. [/EDIT]

Sebastian

The fact that you're concerned and want to correct it, means we'll make a tech out of you yet!

Definitely start checking resistors, without a doubt. On some of them you may have to desolder a leg to get the actual reading. Anything more than 10% deviation (and I would aim for 5% max) is definitely cause for replacement. Use metal or carbon film resistors for replacement, not metal oxide types - they are not good for audio.

And I would check any zener diodes in the circuit. If the circuit diagram specifies BZX types, don't replace them with the more common 1Nxxxx types - I learnt that through experience.

Menahem

You know, that's funny because i was just about to come and declare that whatever it is, it sounds too good to worry about, but of course you're right. I've spent the day listening it, and it's just amazing how nice it sounds after the recapping. I mean, i can appreciate the "better" systems, but it just has this nice and warm old sound. It was this that i was expecting when i first listened to it and was so disappointed. I can just picture it already with an old turntable and listening some records with it (note : next project : turntable 😂 Another note : must find RIAA board). And i know that it'll just get better while the caps burn in.

So it's mainly done. But i kind of would tend to wish to finish it proper, even though i doubt you'd be able to make a tech out of me no matter what happens 😂 So, yes, i'll need to get to it, and just measure every damn thing on it that i can, without expecting that someone holds my hand every time. I'm not even sure this voltage difference really matters in real life, as it works just swell, but i've done already so much on it that it'd be nice to get it just there, to close it and never worry about it ever again.

So thanks for the pointer, i'll go through all the resistors & zeners when i will recap the stereo decoder next week 🤒

Sebastian

sebastian wrote:

I'm not even sure this voltage difference really matters in real life, as it works just swell, but i've done already so much on it that it'd be nice to get it just there, to close it and never worry about it ever again.

Remember those old resistors have a 10% tolerance (some might even be 20%). So you can allow about that much on most test point voltages, as well... of course those that are directly adjustable should be accurate.

Just thought I would say what a great thread this is. Well done to all involved and it may well inspire me to recap the 900 in my Compact.