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This is the second Archived Forum which was active between 1st March 2012 and 23rd February 2022
As I now find a little time on my hands I have decided to look into a couple of issues that have nagged at me for months but, due to no particular requirement, I have largely ignored. Both of my BM4400 units have issues with the radio reception.
briefly the basket case unit (burr veneer) has very good reception and tunes quite well to lots of stations. The tuning lamps both work well too....however the red LED stereo lamp is always on and the radicator does not deflect at all during tuning.
My other unit has very poor reception and only picks up one or two stations, the tuning lamps work fine......however the red stereo LED is always on, the radicator does deflect but wont calibrate to the full 4.5 setting.
The basket case first.....these meters are a little tricky to remove.
Removing the screw and spring to the rear and disconnecting the internal lamp, unsoldering the meter connections allows the meter to be removed, it looks like a sealed unit but surprisingly isnt, comes apart quite easily.
This meter was catching badly in its suspension, moving coil meter, a fair bit of corrosion is present here. A slight dab of railway modellers light lubricating oil freed it off nicely and the spring was returning the needle back to zero when moved manually, at this point I decided to test the resistance of the coil only to find it open circuit.....not good. connected it back in place and sure enough no deflection when tuning was attempted. The DVM confirmed the presence of a voltage when connected across the meter.
So for this one a replacement meter is required.......
Craig: So for this one a replacement meter is required.......
Got one.
Martin
Your a star.....please send me a paypal invoice to cover price and delivery, I will take a look at the other unit in the meantime to see whats going on there ;~)
Craig
Further investigation has revealed that the actual reception isn't as bad as I first thought....comparing the stations picked up by both machines the basket case (the one with the failed S Meter) is picking up more channels and I do believe the reception is better than the other unit (the one with the good S Meter)....additionally the other unit goes silent when the AFC ST is operated.....so something is amiss.....and I still dont know why the stereo LED is always ON .......little guidance here would be appreciated ;~)
Had a go at adjusting the internal oscillator in accordance with the decoder setup proceedure in the service manual, tune into a stereo station and adjust 3C8 in either direction until the stereo lamp goes out....then set 3C8 midway between the two positions.....stereo lamp stubbornly remains on.....maybe IC1 is the culprit
I think I may have discovered part of the problem.....when recapping this board it looks like I have connected the LED green wire to the wrong place on the board....should be going to pin 5 of IC1 and it looks like I have it plugged into TP7 which is pin 10. see the picture I too before recapping and then as it is right now.....unfortunately I'm at work at the moment so cant check, this will eat at me all day ;¬)
This is where it is now......not 100% clear but it looks suspect
Ok...schoolboy error, swapped both green wires over to the correct pins and now both red LED's respond to (what I believe to be) stereo broadcasts, the LED's fade in and out with the signal strength.....so that's good, however the unit with the good S Meter still goes completely silent when the AFC ST switch is depressed and unlike the basket case unit I cant make the LED go out by adjusting 3C8 in either direction to set the internal oscillator....this is now the only remaining fault, I will look further. I cant believe I connected the green LED lead to the wrong pin twice, in my defence the wrong pin is more prominent on the board ;~)
Check the solder joints at the main board, where the plugs for the piggyback boards are fitted.I do also seem to remember soemthing about a black wire to the tuner that occasionally breaks off.
Ok....update on the situation, disconnected the Stereo Decoder & Indicator PC3 and gave it a good check over. No loose pins or wires....so because I can I removed PC3 from the basket case and and connected it to this unit....the problem of everything muting when AFC-ST is switched in continued....this puts PC3 in the clear.
Put basket cases PC3 back in its rightful place and checked it still worked, was fine. Replaced the now proven PC3 and removed IF-Section PC2, carried out thorough check of all pins and wires....all good, took the lid off the Tuner PC1 and checked all solder joints within, all looked good. again because I can I borrowed PC2 from the basket case and wired it in....same problem, puts PC2 in the clear also....replaced the borrowed PC2 back into the basket case and checked all was still well.....worked fine. So I'm thinking PC5 is now in the frame. When AFC-ST is operated both tuning lamps continue to glow and the S-Meter continues to display signal strength the stereo LED is still illuminated....just a perfect silence from the speaker I have connected up...........
The ST in AFC-ST stands for Silent Tuning.It's supposed to be silent between strong stations when the AFC-ST button is down.If it remains silent, even on strong stations, the problem is most likely a too weak signal strength (so the circuit thinks we are not ata strong enough station to release the muting).In other words, we are probably looking at a problem related to the antenna, the frontend (mixer/oscillator) or somewhere along the IF string.It's my experience, that a weak or "sluggish" IF usually points to a problem upstream towards the antenna, whereas problems furtherdownstream towards the detector etc. usually has more drastic effects, like more or less complete silence (without ST).
Right.....following the great mans advice I have removed the entire train from the problem unit, breaking a single strand black cable into the bargain, and exchanged it for the basket case train.....the problem unit complete with basket case train still refuses to play when AFC-ST switch is depressed, everything else is good, LED indicates a stereo broadcast, S Meter deflects fine.....just no sound.
With the problem units train installed the basket case performs great even with the AFC-ST switch depressed....so these boards and associated components must be ok.
This does of course leave the antenna cable itself and the connection at the rear of the unit, I will haul that out tomorrow in order to eliminate it from our enquiry's, it looks fine externally, and of course its fixed with a sort of pop rivet thing that will probably need replacing with some BA nuts and bolts once removed.
That's interesting.Part of the muting circuit is on the main board.
Spent an afternoon with the DVM measuring voltages around the muting circuit and did actually find different voltages around the level indictor twin diodes, the voltages did vary as I adjusted the tuning on both units......thinking back to the recent problem I had on my BM6000 and the wrong bulb scenario I decided to pull the Level lamps and have a look, sure enough some clown had replaced one of the level bulbs with a wrong one! (to be honest it was me during the recap exercise as one was blown ;~) ). I removed a bulb from the basket case and installed it into the problem unit and jackpot!
Flushed with the result I set up the tining indicator lamps using 3R25 to get them balanced and had a play.....its not perfect but I can now operate the AFC-ST switch and maintain an output, I,m not getting all the stations with the ACF on but I suspect this is due to not having everything set up right as yet.
To be sure I was on the right track I installed the suspect bulb into the basket case and sure enough when the AFC-ST is selected all goes quiet......
Martin......I need a couple, make that 4, replacement bulbs and the S-Meter please, if you could invoice me ;~)
I thought to change all the bulbs by LEDs ??? Is it possible without major modification of the circuit? Thanks!
Beo_Jean: I thought to change all the bulbs by LEDs ???
I thought to change all the bulbs by LEDs ???
Why?And no, the lamps are integral parts of the circuit (as also confirmed above), the lamps current flow is essential for correct function.
Why? Because they are a real pain to reach when they go bad. Unless I didn't get it yet but you have to pull the front face to reach them which is not that fun... Do you have those bulbs Martin? Thanks!
It takes less than 2 minutes to replace a lamp.Take off the top cover, pull the socket (or the sockets leads carefully) from inside the Beomaster, pull the lamp from the socket,insert a new lamp and fit the socket back in its holder.See Craigs photo higher up in this thread, where both of the tuning lights sit in their sockets and leads - just pulled in from their holders.
Going in from the front would take a week.
Yes, I have the lamps.
@ Dillen.
Thanks for asking WHY!
The warm color profile of the incandescent lamps is not only part of the electrical design, but also an intricate part of the visual design, no LED can replicate.
Breaks my heart everytime someone applies that mod...
But isn't it ironic ?( Alanis Morissette)
AliExpress seems to be the best place to source the bulbs in quantities...
BEOVOX141: AliExpress seems to be the best place to source the bulbs in quantities...
Yes, but the cheap chinese (no offense intended) "toy lamps" have a typicallifespan of max 1000 hours - and you're lucky if they'll last 100-200 hours.When it comes to quality, you get what you pay for.
And I agree on LED vs. lamps.
It's a general misunderstanding, that LEDs will last forever.They are basically hard working diodes.Many of these Beomasters still have working original lamps.
Dillen:Many of these Beomasters still have working original lamps.
Yeps,- because back then every electrical engineer knew, adding a bit of quiescent current to the filament would make them last longer.
Fun fact: In Denmark, there is a tax imposed on the filament in an incandescent light bulb, The amount is about 40us cents.
Granted,- a small amount, but you can imagine why we never had Christmas lights untill LEDs came around.
Thank you Martin for your answer,
I will order one complete set this week, so far all lamps are working including the overload one... but no smoke yet
Sounds like you have a problem going on there with that overload lamp......
Don't you just love this site....it's like watching one of the Royal Institute Christmas Lectures!
I found the problem and it's a weird one, will post the issue starting another thread...