Beomaster 4000 transistors

Hello.
I have replacement component questions. 

I bought a Beomaster 4000 where the right channel had been nice and toasted. R480, R472 have visually been burned. TR41,42,44,46,47 all test as shorted by my PEAK transistor tester and I'm assuming TR43 is bad too. The two AA143 diodes test as dead too. 

Here is what I think I've found for replacements, I'm newer at figuring out modern replacements for obsolete transistors so if something is wrong please let me know:

TR41, BC212B to BC546
TR 44 BC183B to BC546
TR 43 BC 252 to BC327
TR 45 BC308 to BC556
Diode AA143 to 1N34a or Schottky 1N5711

I haven't found a good replacement yet for:
TR 42 BC312
and the Darlingtons:
TR 46 MJ3001
TR 47 MJ2501

Both diodes 1N4148 tested good. I've already changed the capacitors and variable resistors. I'm assuming to replace the emitter resistors too. Any thing else I should check?

 

BC212B is PNP - using BC546 would be wrong - Use BC556B.
BC183B - use BC546B or BC547B
BC252 - use BC556B
BC308B - use BC556B

No Schottky diodes in output stages - ever!
(or any other places where power is handled for that matter).
AA143 is still available many places. Or use AA138

BC312 - use BC141
MJ3001 and MJ2501 - these are difficult to replace. I suggest using the original types (look for old stock).

What to check? - Pretty much everything.

Martin

Thank you Martin!

Check the bridge rectifiers, change transistors from TR39 onwards, MJ transistors US Ebay, make shure you get BC XXXB types (low noise )

Did you change the 5000 caps ?

Søren Mexico:

Check the bridge rectifiers, change transistors from TR39 onwards, MJ transistors US Ebay, make shure you get BC XXXB types (low noise )

Did you change the 5000 caps ?

Collecting Vintage B&O is not a hobby, its a lifestyle.

I was about to buy some MJ transistors that did not have the BC xxxxb but they had the Motorola symbol on them, probably not low noise then. Looks like I'll have more investigating and component pulling before I can start buying.

Learning question: in the cascade of failing components, would the rectifier fail as a result of the output components failing?

What would the symptoms of a failed bridging rectifier be, I would guess since it could no longer be converting AC to DC and the current would just stop at the failed diode and the receiver wouldn't power on (I haven't even tried to turn it on yet) or would it flood the receiver with AC? In my journeys so far, I haven't had a reason to suspect one of failing.

I am not ttrying to get into a spitting contest, MJ transistors are not BC TRs , if you dont want to check the rectifiers its OK with me, just go on

The rectifier can fail from overloading - and a shorted output stage WILL overload it.
It's rare to see a bad rectifier in Beomaster 4400, though - but possible.
It's diodes so they typically short (rarely open). Either is bad.

BC xxxB;
The last B refers to the hfe-range, not the noise level.
BC549B is a low-noise version of BC546B but there's not a lot of amplification going on in these stages,
so there's really no need for low noise transistors. Won't hurt anything though, and they are not expensive, so
if you have them, fit them.
Don't fit BC xxxC types in DC-coupled output stages.

MJs - make sure to buy old stock. There are SO many counterfeit semiconductors.
I wouldn't buy from Asia for the same reason.

---

These are almost certainly counterfeits:

http://www.ebay.com/itm/1PCS-MJ2501-TRANS-DARL-PNP-80V-10A-TO-3-2501-/192081409774?hash=item2cb8f1b6ee:g:B2UAAOSwo4pYgcjO

http://www.ebay.com/itm/NOS-MJ2501-qty-1-PNP-Darlington-TO-3-Ship-in-USA-tomorrow-/291171363501?hash=item43cb2a6aad:m:mkPwEnp39MEzUgL1mIJoL1Q

These look original:

http://www.ebay.com/itm/MJ2501-TRANSISTOR-TO3-2-PIECES-qzty-/282076526009?hash=item41ad1235b9:g:v~YAAOSwOVpXa0tk

http://www.ebay.com/itm/2-pcs-MJ2501-Motorola-Transistor-TO3-NOS-/331859089075?hash=item4d4457d6b3:g:FfIAAOSw~gRVhoyh

Martin

www.reichelt.de sels those transistors still...

Søren Mexico:

I am not ttrying to get into a spitting contest, MJ transistors are not BC TRs , if you dont want to check the rectifiers its OK with me, just go on

Collecting Vintage B&O is not a hobby, its a lifestyle.

No spitting here about transistors, I'm very thankful for all the good advice, I am a learner and I combined your two first two pieces of advice. From what I've read on this forum about bad transistors I wanted to be extra cautious and thought I was going to order the wrong parts.

marc:

www.reichelt.de sels those transistors still...

No-name goods. Been there.
I suggest buying old stock. Cost a little more, but will save you a lot of trouble.
ACtually, I would rather buy good original used parts than no-name or unknown modern brands.

Martin

Tr 39, and 40 tested good, as did the bridging rectifier!

Upload picture time. Next I need to spend the afternoon desoldering and checking "everything" and more online shopping for transistors and diodes. I wish I could be lazy and just buy packs of commonly used transistors for this era.

Nice project. My BM4000 has been my primary (2 channel analog) receiver for over 5 years now. I love it and have no desire to find something "better." Good luck with your restoration. She looks almost mint on the outside.

And it's the 108MHz version.
Very nice.

Martin