Sign in   |  Join   |  Help

First attempt at Beomaster 2400 'refurbishing'

rated by 0 users
Answered (Verified) This post has 3 verified answers | 48 Replies | 2 Followers

jesperb
Not Ranked
64 Posts
OFFLINE
Silver Member
jesperb posted on Thu, Apr 26 2018 12:39 PM

Hello All,

Starting my first real repair project on a Beomaster 2400 - no previous BeoFixing experience, but lots of electronic DIY. This model came from my Dad, which is why i said yes to try to fix it, besides always having wanted to having fixed a Beomaster by myself (counting on a little help from my friends). It will be a rather long project, because summer is creeping up, but if it rains as much as last year, could be a quick fix after all.

Problem is 'no audio - hissing sound in both channels - volume control does not work'.

Took the lid off last night, things of immediate notice :

-End panel (left) missing - anyone got a spare in dark rosewood ?

-Sliders in really good condition, no dust, no coffee spills - nice and clean.

-Bass section, ceramic caps are 'crushed' (see pics) ?

-Output trannies (IC200,201,300,301) have been repaired previously and BADLY resoldered.

Cheers,


Beogram TX, Beovox S45, Beovox MC 120.2, BeoSound 1, CX50, Beovox S75, Beomaster 2400

Answered (Verified) Verified Answer

Dillen
Top 10 Contributor
Copenhagen / Denmark
10,762 Posts
OFFLINE
Founder
Moderator
Answered (Verified) Dillen replied on Thu, Apr 26 2018 2:50 PM
Verified by jesperb

The polyester caps are not part of the kit. They are usually still fine.
And it's not uncommon to see cracks and flaking off of the outer layer of the "tropical fish" types - though in this case it
seems to be a bit more than usual. You could replace them, but I wouldn't suspect them at this point.

Capacitors and balance control slider much more likely.
But of course, any and all signs of previous repairs should be looked at - and in this case tidied up a bit.

If the lamps are still the original, you will need new ones when you are done servicing the rest.
The filaments in the old lamps become brittle from heat and age and the unavoidable vibrations from servicing will
break some. Replacing those will then break more. You have a fresh full set, might as well replace the lot - but wait until
repairs to the Beomaster is about done.

Martin

Dillen
Top 10 Contributor
Copenhagen / Denmark
10,762 Posts
OFFLINE
Founder
Moderator
Verified by jesperb

The balance potentiometer is special in that it operates from the center outwards, - and with the channels in antiparallel, rather than
from one end to the other in parallel.
In other words, at center position both channels should read zero ohms.
As you move the slider left the resistance in the right channel increases while the left remains at zero - and vice versa.
You lower the signal in one channel in each direction from center. At center no channels are lowered.

The resistive tracks only varies from the center towards each their ends. The other ends (respectively) of the tracks doesn't vary.

Martin

Dillen
Top 10 Contributor
Copenhagen / Denmark
10,762 Posts
OFFLINE
Founder
Moderator
Verified by jesperb

If the Beomaster will switch on briefly - even if only for a fraction of a second - you should be able to tell if one output has
a high DC level, pointing to a problem in that channel.

Martin

All Replies

jesperb
Not Ranked
64 Posts
OFFLINE
Silver Member

Hello and thank you,

Yes, i understand in-circuit testing is not the holy grail for tranny testing. But i needed to start somewhere and since Peak was the tool at hand, I used that (plus forgot all about the DC-out measurement).
My apologies, but  i am still trying to teach my brain to listen to good advice ;-)

I have a little problem measuring DC-out with a DMM though. Standby occurs a bit too fast for my (cheap) DMM to follow - even for an overload in the selected range.  May need to find an analogue one.

Beogram TX, Beovox S45, Beovox MC 120.2, BeoSound 1, CX50, Beovox S75, Beomaster 2400

sonavor
Top 50 Contributor
Texas, United States
3,132 Posts
OFFLINE
Gold Member

To capture momentary signals you need an oscilloscope. Modern digital scopes can capture and store events like that.

jesperb
Not Ranked
64 Posts
OFFLINE
Silver Member

Before i messed up the Beomaster,  DC-out was around 20mV for each channel, with sound in one channel and sound in both earphone channels. So i assume, measuring one output with your analogue meter in ex.100mV range, take the Beomaster out of standby, would give a full scale reading for a short burst, before the overload circuit triggers a standby again. This would indicate too high DC-out=short somewhere in the output stage for that channel (?)

Beogram TX, Beovox S45, Beovox MC 120.2, BeoSound 1, CX50, Beovox S75, Beomaster 2400

jesperb
Not Ranked
64 Posts
OFFLINE
Silver Member

To show i actually DO listen to advice given, i have ordered a scope - It has been on my wishlist for too long anyways, so thank you for the friendly peer pressure Big Smile

Beogram TX, Beovox S45, Beovox MC 120.2, BeoSound 1, CX50, Beovox S75, Beomaster 2400

jesperb
Not Ranked
64 Posts
OFFLINE
Silver Member
jesperb replied on Sat, Jan 19 2019 10:54 AM

OK, finally got a Rigol scope from a nice German webshop. After some fiddling around with the triggering, hadn't touched a scope in +20 years, i managed to get these DC measurements.
Measured directly on the PCB. GND at C92. Measuring points 7(left ch)+8(right ch) and switching on with FM5 :
Pt 7, left : 260mV
Pt8, right : 240mV

Just to make sure, i measured twice. The second time i turned on with FM5, for measuring the left channel, it looks like the power went completely - including no light in the standby LED. No smoke, no burning smell, just nothing. I guess it is time to go back and start checking the power supply...

 

Beogram TX, Beovox S45, Beovox MC 120.2, BeoSound 1, CX50, Beovox S75, Beomaster 2400

jesperb
Not Ranked
64 Posts
OFFLINE
Silver Member

Took a look at the 15VDC fuse : burnt and one metal cap came off, hen i took it out. New fuse and power+standby OK again.

After some fiddling with the new scope, i got these two measurements of DC-out on the two measuring points on the PCB (speaker out).
Not measured directly from the plugs, because the speaker pair select switch is broken, so no signal there.
Triggered/measured when switching power on with the power slider switch. Quite some DC out, so something wrong in both output stages (?):

Right channel  :

Left channel  :

Cheers,

Beogram TX, Beovox S45, Beovox MC 120.2, BeoSound 1, CX50, Beovox S75, Beomaster 2400

jesperb
Not Ranked
64 Posts
OFFLINE
Silver Member

Finally got some spare time and got the 2400 out of the closet.
Pulled the cooling fans off the output transistors and desoldered them all (IC200,201,300,301). Actually a lot easier than i would have thought, lesson learned. First one (IC200) came out in two parts, see the picture below and the Peak DCA75 measured it as 'no component detected' - go figure....

Because of this next out was TR213 (MPSA06), which also measured out as 'no component detected'. 
Right channel, IC300,301,TR313 all measured out OK.

Time to replace the bad transistors and see if I can get power on.

Beogram TX, Beovox S45, Beovox MC 120.2, BeoSound 1, CX50, Beovox S75, Beomaster 2400

jesperb
Not Ranked
64 Posts
OFFLINE
Silver Member

After some deliberation, I turned the Beomaster on. It turned itself off immediately and gave a blue puff of smoke. Plus one of the 220VAC fuses blown.
Finally i did, what Dillen has told me (and many others) to do from the start : Test/measure all components in the output stage.
Nothing seemed to be burnt though. Transistors good, diodes good, all resistors good.

I could only think of two things :
1. I had re-used the 'non burnt' TIP 146/IC201 plus a new TIP141 for IC200.
2. I hadn't put the tone-control PCB back in (forgot or...Sleep).

While i was at it - lessons learned - i tested all 15V supply transistor and diodes.
Tested all transistors and diodes in the overload protection too.
Gave the transistors on the volume board (PCB3) a check, because i had previously noticed, the 'volume down' lamp didn't really indicate volume down. Sure enough, 3TR12 measured out with a hFE of 5 (??), so in with a new one. In with two brand new TIP141/146 for IC200/201and the Beomaster lights up fine.
Current usage on the variac say 'just below' 200mA and steady - at least for the couple of minutes, i dares keeping it on. Now ready for BIAS adjustment.

My unqualified guess is, the Beomaster started up on something like full volume, either because of the missing tone-control board or the defective 'volume down lamp driver' and blew the fuse.

Beogram TX, Beovox S45, Beovox MC 120.2, BeoSound 1, CX50, Beovox S75, Beomaster 2400

jesperb
Not Ranked
64 Posts
OFFLINE
Silver Member

After the no-signal current adjustment, the Beomaster is playing nicely. However, the left channel with new TIP's is running sligthly hotter than the right. Playing at half volume for about 30 minutes, the cooling fins, for the left channel, are at 32-33 degrees, where the right channel fins, they are at 28-29 degrees.

Is this business as usual or should I dig deeper into this ?

If not, it is time to dig out - and test - the remote control.

Beogram TX, Beovox S45, Beovox MC 120.2, BeoSound 1, CX50, Beovox S75, Beomaster 2400

jesperb
Not Ranked
64 Posts
OFFLINE
Silver Member

Having done the no-load adjustments, a bit fiddly without multi-turn potentiometers, heating is practically the same on both sides. So time to call it over & out, thanks to everyone who pitched in with their 2€ Big Smile

Beogram TX, Beovox S45, Beovox MC 120.2, BeoSound 1, CX50, Beovox S75, Beomaster 2400

jesperb
Not Ranked
64 Posts
OFFLINE
Silver Member

Just as soon as i got the lid back on, new issue : Sometimes the sound mutes, when i turn the volume up. Only if i touch volume up shortly, like nudging a single step up in volume. Keeping the finger on volume up and it works just fine.
Volume down doesn't have this issue, at least i have not been able to provoke it.

I desoldered and measured all transistors out on the volume PCB (#3), all measures out OK. All diodes too.
I have 18V/100kHz at 3C11/C12. Voltages on the 'input' side of 3IC1 seems to be fine according to numbers on the diagram.
Haven't touched the output side of the MC14516 yet.

Any suggestions as to what can cause this and/or how to troubleshoot this ? 

 

Beogram TX, Beovox S45, Beovox MC 120.2, BeoSound 1, CX50, Beovox S75, Beomaster 2400

jesperb
Not Ranked
64 Posts
OFFLINE
Silver Member

Not sure this is troubleshooting progress, but tapping 'vol up' will activate the mute circuit. Can be reproduced from when volume has been off completely and until there is 'a little' voltage out of the counter (3IC1) pins QA-B-C-D.
The scope screenshot shows the mute out signal, PCB3 between 3R28 and 3R28a. Far left volume is all the way down, tap 'vol up' slightly and 'mute' goes 'high' or 'on'. Then mute is 'released' when i tap 'vol up' more firmly. Finally mute is activated again, with a light tap of 'vol up'. This can be reproduced quite easily.

Beogram TX, Beovox S45, Beovox MC 120.2, BeoSound 1, CX50, Beovox S75, Beomaster 2400

jesperb
Not Ranked
64 Posts
OFFLINE
Silver Member

Not sure this is troubleshooting progress, but tapping 'vol up' will activate the mute circuit. Can be reproduced from when volume has been off completely and until there is 'a little' voltage out of the counter (3IC1) pins QA-B-C-D.
The scope screenshot shows the mute out signal, PCB3 between 3R28 and 3R28a. Far left volume is all the way down, tap 'vol up' slightly and 'mute' goes 'high' or 'on'. Then mute is 'released' when i tap 'vol up' more firmly. Finally mute is activated again, with a light tap of 'vol up'. This can be reproduced quite easily.

Beogram TX, Beovox S45, Beovox MC 120.2, BeoSound 1, CX50, Beovox S75, Beomaster 2400

BEOVOX141
Top 150 Contributor
Denmark, West
482 Posts
OFFLINE
Silver Member

On the subject of the 2400.

What is the recommended bulb replacement?

5mm 12V/1W ?

jesperb
Not Ranked
64 Posts
OFFLINE
Silver Member

Honestly ? I don't know.
I bought them as a 'Beomaster repair kit' and no markings.
Try do a search, lots of discussions about the lamps.

Beogram TX, Beovox S45, Beovox MC 120.2, BeoSound 1, CX50, Beovox S75, Beomaster 2400

Page 3 of 4 (49 items) < Previous 1 2 3 4 Next > | RSS
Beoworld Security Certificate

SSL