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Old 19th August 2004, 09:27 AM   #1
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Default Soundcraft 200b Refurb

I am attempting to reburbis a soundcraft 200b 8 channel mixer, but cannot find the schematics or signal flow diagram which i need to trace a particular problem with the monitor section of the mixer. does anybody know where i can find the schematics foir this mixer? it would be very helpful.

the problem with the monitor section is that if you press any one PFL button the PLf light comes on but no sound comes from the either the headphone output or the c/room ouputs on the back. However is you have more than one PFL button on you do get a signal from both outputs you don't hear anything at first but after a while you get distorted snatches which become more constant untill the output seems perfectly normal.

also the PFL light never completly goes out put stays constantly on but very dim - ?!?!

if you have any knowlage of this mixing desk i beg you to contact me.

therocklobster1600@hotmail.com

thankyou
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Old 19th August 2004, 02:19 PM   #2
AuroraB is offline AuroraB  Norway
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The 200B has a standard virtual ground summing bus for the monitor, - i.e. if you press more than one PFL you will have a sum signal of all selected PFLs. The problem indicated could stem from one or more shorted ellytics, either in the bus feed of the input modules, or something around the summing amp of the monitor section, - located in the main module. If the problem is not conclusively related to one or more specific input modules, I suggest there is something fishy with or around the summing amp. I beleive the pins conncting to the backwire harness are marked, so that you should be able to follow the pin backwords through the bus feed resistor to find the respectice IC in the input modules. Likewise, it should be easy to find the summing amp in the main module...

I have a 400B lurking, manual included, which is a larger version, but have hard access to a scanner............
Any good band repair shop that have been around for a while, should have a manual, as both the 200 and 400 series was quite popular in the early 80s...
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Old 20th August 2004, 01:20 PM   #3
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cheers, ill look into that in a mo,
ive heard of a "pot spray" that is supposed to fix noisy/worn out potentiometers is it any good? is it worth a try? i have not seen any electrial supplyiers that sell 100mm 10k faders. I have done some soldering on most of the group output boards and the LH master, most of the solder joints had cracked, mostly the pots that the board hangs off, this has fixed most gremlins of the desk and i will be looking into the monitor section in a mo,
thankyou
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Old 20th August 2004, 02:18 PM   #4
AuroraB is offline AuroraB  Norway
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Contact cleaner spray could do the trick... the original faders will collect some dust through the top slot, over time. A thorough cleaning with compressed air and contact cleaner is one possibillity. Just don't blow too hard! If it is just dust and dirt, it might do the trich,- if the carbon tracks are pitted or just hard worn, it is at best just a small delay of the problem.
Make sure you clean the carbon tracks, and not just the steel support rod!
The only place I know that currently stock the original Alps faders are here in Scandinavia! But they are in Swededn within EU, but I'm afraid they are appx. 40£ a piece.....

( http://www.elfa.se/elfa-bin/setpage....ok=2012628.htm )
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Old 20th August 2004, 05:32 PM   #5
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Hi TheRockLobster.

I can't help You with a schematic, not the actual problem, but I've found this.

User's guide:
Mods:

Hope it can be of any help.
Good luck with Your project.
__________________
Regards
Hoffmeyer ;0)
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Old 20th August 2004, 07:35 PM   #6
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yep those are the faders allright, pity at £40, thats harf the amount i got the desk for! i think i will try the pot spray, thankyou for the links to the soundcraft website plus the modification page.
the desk come from ebay, which i recommend highly, soundcraft desk for £80, bargin!

heres a little picture of the desk when i got it, its in many bits now
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Old 21st August 2004, 03:38 PM   #7
AuroraB is offline AuroraB  Norway
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Those faders was reasonably expensive 10 years ago,--- appx 30£ then...

About the monitor problem,---when I saw the mod link, it all came back to me-;
The PFL is controlled by the PL-ENable line, which swithes the monitor output from mainmix to PFL. This is a logic signal, - pulled to ground to activite, I think........in each module.
The swithing is done in the monitor/main section by a CMOS IC, ...
just don't recall what number. The delay action can be a result of some fault in the pull-down and/or conrtol signal for the switch...
Will try to dig out the 400B manual
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Old 22nd August 2004, 02:10 PM   #8
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heres a little scan of my master board (RH master), intresting, i still havent actually tried to fix it yet, ive been working alot recently (only part time, but its alot to me, only being 16) good side of that is that i now have a little more money to spend :-)

the ic's on the master board are as follows, also this is a little guess of mine of what they do... probably woring but anyway.

NE5532N ....this is near the oscillator controls ...
TL073CN ....i think this one is the vu meter driver...
NE5532P ....there are 7 of these on the board ...
TL071CP ....two of these, near the talkback mic, and in the middle of the board ...
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Old 22nd August 2004, 02:19 PM   #9
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err, no picture then, ill try again later
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Old 22nd August 2004, 02:33 PM   #10
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here it should be,
seeing as i have got the desk in many many bits and all of the input modules are out, is there any other mantanance i should consider doing?
most of my input boards are issue 10 but two are issue 12, one of which has been repaired previoiusly, due to the Ic's now being resident in sockets, and some caps have been replaced together with some pcb tracks having been soldered. i have managed to aquire 2 more input modules from ebay as spares, and also to replace the standard knobs that i am missing anyway.

i have started to construct a new power supply for the desk, seeing as it did not have one and i have been using a citronic psu for the meantime. i im unsure of the actual current requirements of the desk so i have 1A at 15V split rail for the supply i have used regulator Ics for a stable 15v output and a toroidal 18-0-18 transformer i think that 1A should be enough, although the 300mA citronic psu struggled abit. i am not bothering with 48v phantom power, becuase i don't use it and it would be too much hassle anyway.
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