ARCHIVED FORUM -- March 2012 to February 2022READ ONLY FORUM
This is the second Archived Forum which was active between 1st March 2012 and 23rd February 2022
First og all thank you to Beoworld for the membership.
I've salvaged a MX4000 (type 9150) speakersystem and the corresponding stereo-PCB and want to make it work as a stand alone laptop speakersystem.
I have some experience in the restoration of stereo amplifiers from the 70' and 80', but when is comes to Stereo IC like the LM1876, I lack some knowledge in making it Work.
I've been doing some searching here on the site and found two articles that came pretty close.
#1: first article was on how to salvage the speaker system of an Beovison Avant - which comes down to finding a way to keep the "mute" pin satiesfied.
#2: second article was a dutch article on how to do it for the MX7000 speakersystem - however it has an older stereo-module in the direction of "STK4122" which has slightly more pins.
So now down the MX4000 system.
The Stereo-PCB and speakers worked as they should before salvaging. (=no HW failure expected)
The connectors P31 and P32 goes towards the speakers. (everything is OK there)
The power-in connector P30 is configured as:
Pin1: VCC (A&B)
Pin2+3: Mass connection (common)
Pin4: VEE
I've here connected Pin 1 and 2 to an external power supply @ 21VDC and limited at 300mA
I've measured that the "mute" pin6 and pin11 on the LM1876TF are connected to ground.
And obviously this isn't enough because no sound comes from the speakers.
Question:
#1: How do connect the input voltage at P30 correct in order to accommodate for the -20VDC/+20VDC supply.
#2: Do I need to take some action regarding the "standby Pins" Pin9 & Pin14 - and make sure that the Stereo-power-amplifer becomes active.
any other suggestions are welcome.
Kind regards
Lars
Hi Lars
Is the amp based on the TDA 2040 chip ?
BV6_Fan:First og all thank you to Beoworld for the membership. I've salvaged a MX4000 (type 9150) speakersystem and the corresponding stereo-PCB and want to make it work as a stand alone laptop speakersystem. I have some experience in the restoration of stereo amplifiers from the 70' and 80', but when is comes to Stereo IC like the LM1876, I lack some knowledge in making it Work. I've been doing some searching here on the site and found two articles that came pretty close. #1: first article was on how to salvage the speaker system of an Beovison Avant - which comes down to finding a way to keep the "mute" pin satiesfied. #2: second article was a dutch article on how to do it for the MX7000 speakersystem - however it has an older stereo-module in the direction of "STK4122" which has slightly more pins. So now down the MX4000 system. The Stereo-PCB and speakers worked as they should before salvaging. (=no HW failure expected) The connectors P31 and P32 goes towards the speakers. (everything is OK there) The power-in connector P30 is configured as: Pin1: VCC (A&B) Pin2+3: Mass connection (common) Pin4: VEE I've here connected Pin 1 and 2 to an external power supply @ 21VDC and limited at 300mA I've measured that the "mute" pin6 and pin11 on the LM1876TF are connected to ground. And obviously this isn't enough because no sound comes from the speakers. Question: #1: How do connect the input voltage at P30 correct in order to accommodate for the -20VDC/+20VDC supply. #2: Do I need to take some action regarding the "standby Pins" Pin9 & Pin14 - and make sure that the Stereo-power-amplifer becomes active. any other suggestions are welcome. Kind regards Lars
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Hello Beovox141,
Thank you for your interest and your Reply.
No it is LM1876TF which is commenly used in the newer MX4000, and all MX8000, BV3, BV6 & BV7 TV sets.
According to spec it requires min 20V and max 64V to operate proporly, it is a stereo IC which means it can handle to speakers. (the MX4000 only has 2 speakers), and it has 15 Pins.
Regards
Lars , West-Denmark
Hello Michael,
Very interesting page.
Regards Lars
Dear all,
I've pinpointed one problem - the Power input.
I've now manged to find at good stable Transformer with 2 outputs at around 20VAC. (Comes from an old AKAI BASIC-X1 Casette deck dated 1991, Type L01-3304-05, TKP0228-91)
My question is fairly simple. My Transformer has three outputs. Wenn I Connect it to the main grid power on the Primary side I can on the secondary side measure:
Between Pin1 - Pin2 = 20,53VAC
Between Pin2 - Pin3 = 20,53VAC
Now for my MX4000 amplification board (which has 4 Pins, & Pin2+3 are common ground) I Need a +20VAC Connection for PIN1 AND a -20VAC for PIN4.
Question: How do I know which one is the "+" and which is the "-" terminal (when both measure a positive VAC value) OR doesn't it matter because the Phase will Change 50 times per second anyway?
Looking forward to a Response.
I needs a split supply! Vcc is the postive e.g +20V Vee is the negative e.g -20V
The idea is the input GND/signal is in the center of the suppply (0V) witch allows the output to swing from -20v to +20V.
There is no power audio amplifier in the Beosystem 3 or Beovision 7 since they do not have internal speakers.
The LM1876 replaced the Sanyo Hybrid blocks in most B&O products. The successor was the famous LM3886 (aka the gain-clone) its more powerful, has more protection and a mute circuitry.
I dont have a schematics of a MX4000 output board only the TDA2040,- perhaps you could share a picture?
I would make assistance a lot easier...
BV6_Fan:I've pinpointed one problem - the Power input.
You need to build something like this,- note the symmetry around GND! Forget about the actual values in this schematic, but note the output at the caps will be approximately 1.5 times higher than the AC value you are measuring at the trafo.
We probably just wrote/send at the same time.
I'm sorry - i dont have a schematics but I agree all the way.
Now comming back to your first sentence (mail 9:44) and my Question (mail 9:40) - now ground is clear, but do I Need to worry About which is PLUS and/or MINUS when hooking up the Trafo to the amplification board?
Thank you again for your Reply (Mail 9:52).
Something like that makes perfectly sence. I'll give it some thoght and make a test Setup.
Thank you for the quick Reply.
BV6_Fan: Hello Beovox141, Thank you again for your Reply (Mail 9:52). Something like that makes perfectly sence. I'll give it some thoght and make a test Setup. Thank you for the quick Reply. Regards Lars
As long as you can identify the center-tap correctly the two others are indifferent! The Graetz diode bridge takes care of the polarity, try following the current flow in the schematic, its magic
The trafo is most likely way to small but it will work for now, if you get the the amp running, abort when it gets really hot
It might be worthwhile simply getting it from Ebay, shipping of parts in Denmark is properly more....
https://www.ebay.com/itm/Audio-Power-Supply-Amplifier-Board-35A-10000uf-4-50V-Diode-Rectifier-Filter-Amp/182127030198?epid=1586618401&hash=item2a679defb6:g:2PkAAOSwmcBa~kKD
I believe that you're right About the trafo being a Little bit on the small side.
But what happens if I where to take a much bigger Trafo (like the 310 Watt trafo out of an ONKYO TX-SV545). Then it would just be idling all the time.
I think I'll start of with the current trafo - and cut out when it gets really hot as suggested.
Hi Beovox141,
After looking through my dozens of (paper-) TV schematics I found out:
Obviously he's talking about an MX4200 according to the type number he mentioned.
For MX4200 there seems to be only an "onsite manual" without schematics.
That's when B&O started to only swap modules so (in their opinion) no need for details
I'd like to stand corrected
The MX4000 / MX4000 Beo4 / MX4002 are all using the TDA2040 you mentioned...
Gunther
Thanks Gunther
I was looking at the MX4000 schematic and that is exactly why I thought the amp was the TDA (ST) type.
I wish people would post a picture it makes helping out so much easier.
To be honest: I think the whole swapping thing started because B&O literally lost control of their configurations
Thank you all three of you for your replies.
@Gunther: you're right - it is a MX4200. However I can't find a way to Change the Headline - so ill leave it as it is.
Based on the recommandation I got here in this forum I've gotton a step further. (I'm trying to upload some Pictures in the media forum - but receives the a message saying "Error...we are sorry that you get this message...try again in 30 Minuter". So I'll try again later uploading some good images.
Briefly About the newly build rectification:
It consistst of a RBV-402 Rectifier bridge, 2 Phillips 40V 4700uF & 2 220nF 63V capacitors, and 2x 3,15A fuses.
This gives in total an Rectier output voltage of -28,8VDC / 28,8VDC respectively. When the MX4200 Soundboard is connected it drops down to -27,1..27,1VDC (Hower the LM1876TF only requires a Little over 20VDC to process the Music. So it should be OK)
The ELKOs on the soundboard are also being charged correctly and he I can measure a voltage of -27,1V..27,1V respectively.
A CD player is conected through the cinch connectors under the front of the speakers - but no sound is comming out throgh the speakers.
At the Pins of the LM1876TF stereodecoder i measure the following DC-values (towards mass which is the mass of the soundboard) when the CD player is playing.
Pin01: 26,6 VDC
Pin02: 9,74V
Pin03: 0V
Pin04: 0V
Pin05: from 6..40mV and increasing
Pin06: 0V
Pin07: 9,76V
Pin08: 0V
Pin09: 0V
Pin10: 1,681V
Pin11: 0V
Pin12: -26,55V
Pin13: 0V
Pin14: 26,55V
Pin15: 0V
IS there anything that Comes to mind when Looking at thosse figures? Any input would be highly regarded.
The configuration of the stereo Decoder pinning can be seen on the homepage of Texas instruments.
http://www.ti.com/lit/ds/symlink/lm1876.pdf