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This is the second Archived Forum which was active between 1st March 2012 and 23rd February 2022
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, Beomaster 5000, Beogram 5005
Output stage bad soldering
Great! Another project showing up!
Things I'm noticing from the pictures are:
- ROE red capacitors --> changed them asap.
- The cracked capacitors are not ceramic but metallized polyester (MKT): Depending on the values, you can use Vishay MKT1822 or MKT369 but you can also use MKT brand as well.
- Really bad soldering on the output transistors but you may want to check them to see if they were properly matched...
Hey,
Thanks for the input - i simply couldn't remember what that type of caps were called in techspeak :-)
I will check the output stage transistors, before or after recap ?
Already got a kit of caps + lamps + slider holders from Martin/Dillen. Lamps and sliders will not be needed though, both parties look to be in really good shape.
Thanks,
Ask Martin but I don't think the cracked capacitors are part of his standard cap kit...
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 itseems 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 willbreak some. Replacing those will then break more. You have a fresh full set, might as well replace the lot - but wait untilrepairs to the Beomaster is about done.
Martin
OK, polyesters are just flaking - never seen them so bad before though.
Looking at the rows of caps in the kit, it's like i'm the richest man in the world - uncharted territory ahead.
Will clean sliders.
Will swap the lamps as the last task - but first a long weekend off.
Nice hint about the lamps, and common sense, put in another context : I recently busted my last glow lamp, bumping it around a bit with the vaccuum cleaner.
Thanks very much, enjoy.
I may have an end panel. Are you in the US?
Thanks for offering, but we found the missing panel in the attic. Turns out the panels are black - not wood
PS I am in Denmark
Not original in black. They were painted then.The serialnumber label will usually tell the original finish.
Didn't notice - nice paint job or i need better glasses (probably the latter) ...
Model/type : NR 2400/2901
s/n says : No 15130001 SIGN E4 (in blue ?)
Originally light oak.So the backsides of the plastic panels will be a beige color.
Update : So the 2400 has been in the closet for more than six months, awaiting dark and cold nights, best fit for a soldering iron etc.
But come November, I am well into recapping, with the kit from Dillen (thank you!).
A practical question : Does anyone have an easy way to locate which soldering points belong where, when unsoldering ?
For reasons unknown, i have some trouble hitting the right points. Could be lack of practice.....
New slider bridges (also from Dillen) were quite easy to swap, lamps also went fine.
In the meantime, I got a really (really) old Metric variac,i plan to/hope to use for the testing. All including dust, spiderwebs and black fuses. New 3A fuses took care of that, at least for now.
Have a nice weekend :-)
Looks like the previous 'repair person' was somewhat of a brute for quick (& dirty?) solutions.....
Not all of the old caps were happy-campers...
After a LOT of fiddling with the touch panel, i finally got all the small 'forks' connected to their respective pins. Now power up through the variac, got standby and LIGHTS!Switch to 'ON', no smoke, no excessive heat on the ribs or anywhere i can measure. Adjust TP15 to 15V (was 14,68 not too shabby).
Now : who the he.. has an FM antenna lying around these days
I guess this is where the real work starts
-Left channel dead. Tried swapping speakers and tape channels (DIN<->RCA plug). Only sound in the right channel.-Sound fades completely out when i push the balance slider past the 'middle' position (see pics).-Sound in right is very 'muddy' when i turn up the volume.-PSU looks fine : C92=19,7V, TP14=11,7V,TP15=15,0V,TP16=15,6V,+-31V also OK, -No-load emitter resistor voltages are : R256=-4mV, R356=-12mV. Didn't dare try to adjust just yet. Besides the emitter voltage doesn't change after about 10 mins of power up, no speakers attached.
First, I'm thinking the balance slider (22kOhms) is broken mechanically, as it shorts out halfways in both sides (slider bridge is already replaced with Dillens kit)? Compared to the treble slider (also 22kOhms) which measures a nice linear 0<->20kOhms in both sides on bottom pins E-S.
Any thoughts on this most welcome, thank you ?
First, I'm thinking the balance slider (22kOhms) is broken mechanically, as it shorts out halfways in both sides (bridge is already replaced with Dillens kit)? Compared to the treble slider (also 22kOhms) which measures a nice linear 0<->20kOhms in both sides on bottom pins E-S.
The balance potentiometer is special in that it operates from the center outwards, - and with the channels in antiparallel, rather thanfrom 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.
Thanks Martin. After your suggestions, it was MUCH easier to search for your handfuld of similar answers to this exact same question
I soldered out all sliders (again) and game them an extra cleaning. Measured resistance and is was as per the specs.However, same issue : very'muddy' right channel, no sound in the left.This goes for both phono and tape inputs.
Turning down bass+treble doesn't change the 'muddyness', so my conclusion is, it has nothing to do with the sound adjustments (?)
Tried earphones, sound quality is much better, only a little 'muddy' in both L+R. Headphone balance works sort of in reverse though, little lower in the middle, little higher in both ends.
As soon as i get DIN+RCA plugs i will wire up a cable and listen to tape-out through my 'normal' amp, to isolate further.
Stereo switch - does that have anything to say here ?Jesper
Did a read-up on 'all' 1900 and 2400 posts in the forums and sure enough : I'm testing input from TAPE with a 7-pin DIN....
The crushed polyester caps on the control board (see first post+pic) were - well crushed.New ones in and the sound in the right channel is now finally good. Sadly the new ones are same form factor, so they will be crushed too. Anyone who can recommend another makeor smaller size ? EDIT : I see Beo_Jean already gave recommendedations here earlier.
Very low sound in left channel. Sounding somewhat like cross-over ?
This post should change subject to 'Collateral Damage' : Ground wire pulled out in one speaker cable plug. Took some time do debug. Volume control right lamp stopped working and volume touch control started behaving erratically. Took no time to debug.
More collateral damage : Dropped the trafo-end of the Beomaster - rather clumsily - onto the working table. Just a small bump from about 10cm's, but all lights are now out, except the standby LED. When choosing ex. TAPE the relay clicks and the Beomaster goes back to standby immediately. Must be the error detection circuit doing it's job.I guess something short-circuited or a lamp broke. Will start checking power and then lamps
Check output stage transistors solder jointsand also where the transformer leads are soldered to the fuse board.
Transformer leads are (and were) soldered fine. Output transistors soldered fine. I had already resoldered both before the mishap (know this is not a guarantee, so i triple-checked).
PSU measurements in standby are : C92=21.8V (maybe a little high ?), TP14,TP15=0V (unit in permanent standby), TP16=15,4V, TP17=15,3V.
Checked all lamps, even though i see they influence more when the 2400 will not be going into standby.
Time to measure output transistors ? In-circuit measurement OK or pull them out ?
Sorry for the basic questions, not the most experienced, in electronic trouble shooting.
Got a Peak DCA Pro semiconductor tester and did an in-circuit test of the output stage transistors+diodes. Marked the results on the pic : green=transistor tested OK, orange=Peak found no component. I also checked the transistors 'not detected' with the multimeter in diode test and then ohmed them out for shorts. I found no shorts and voltage drops for BC and BE looks to be 'normal', for a diode.
Any other suggestions, before i start desoldering the 'orange marked' trannies and give them a new test ?
PS More collateral : The manual output switch came apart as was i trying to measure, if it had a short. The previous repairman had done a proper job of destroying it. Spared me the emberrasment though.
No in-circuit test will be reliable in circuits as complicated as this.Doing some DC-level readings would tell much more.
Which - for reasons unknown - I didn't measure after the 'standby only' issue occurred Will return with DC-level readings on the output tonight, thank you.
Just to add to what Martin said, the FAQ for the Peak Atlas DCA Pro says that it cannot do in-circuit transistor testing.It is a nice meter, I have one, but also be aware that transistors that are detected and measure good outside the circuit board can still be faulty. I have run into that a few times. It's no fault of the Peak meter but rather a failure scenario of a transistor. Sometimes their fault is under the load of a circuit. That is why measuring and looking at the voltages for various operating conditions is a better test in that case.
-sonavor
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 hasa high DC level, pointing to a problem in that channel.
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.
To capture momentary signals you need an oscilloscope. Modern digital scopes can capture and store events like that.
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 (?)
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
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 : 260mVPt8, 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...
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 :
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.
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...). 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.
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.
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€