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Old 1st Jan 2019, 2:46 pm   #1
ITAM805
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Default MN3007 BBD chip

Happy New Year

my neighbour has ask me to try and fix this 1970/80's EH Small Clone chorus pedal. After finding a broken wire and a dead LED 'on' indicator (which confused me) I traced the signal to pin3 of the MN3007, but nowt coming out of pins7/8. The clock inputs are both getting square wave signals, and power is on pin1 so I presume it's a duff chip, but is it?

The MN3007 come in around £10 each and also are on the list of most faked, so I dont want to spend out only to find it's something else that I'm overlooking.

The schematic shows the MN3007 (arrowed by me), this is factory mod not and not part of a hatchet job!

Many thanks
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File Type: pdf EHXSmallCloneSAD1024AMN3007-FactoryE.pdf (52.0 KB, 134 views)
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Old 1st Jan 2019, 3:35 pm   #2
Marconi_MPT4
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Default Re: MN3007 BBD chip

Hi

Are the two clock inputs CP1 (pin 2) and CP2 (pin 6) also present derived from CD4047 mono/astable multivibrator Q and /Q outputs pins 10 and 11?

Rich
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Old 1st Jan 2019, 8:54 pm   #3
ITAM805
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Default Re: MN3007 BBD chip

Hi Rich

yes p2 and 6 are getting the clock pulses. There is a faint low level clock pulse on the o/p (7&8) but no audio
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Old 6th Jan 2019, 10:13 pm   #4
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Default Re: MN3007 BBD chip

Update, I stuck the new BBD chip in and was now getting healthy square wave pulses from the output pins 7/8 but still no audio

I noticed that this pedal had been got at (understatement) and wondered if the audio driver bias trimpot has been 'adjusted' - it had, a little tweak and the sweet sound of vintage chorus came flowing from the monitor speaker
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Old 9th Jan 2019, 11:50 am   #5
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Default Re: MN3007 BBD chip

As a matter of interest, was the fault the BBD chip, or actually the bias adjustment? Did you try the old BBD back in after you had got it going by adjusting the (already tweaked) bias pot?
Out of curiosity I ask this, as I have over the years had many Japanese synths and organs to repair, and had very few MN300x I.C.s fail.
I'm surprised the MN3007 is on the list of often-faked I.C.s, as they are not really a high-volume seller, I would have thought, therefore not profitable to fake. Tony

Last edited by boxdoctor; 9th Jan 2019 at 11:55 am. Reason: text adjustment.
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Old 9th Jan 2019, 12:36 pm   #6
ITAM805
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Default Re: MN3007 BBD chip

Hi Tony

the pedal has gone back to my neighbour, but I can say with certainty the chip was duff as there were no clock pulses on the o/p of the the old one, there was with the new one fitted - prior the bias adjustment.

The neighbour, a guitarist, reads stuff the many forums out there on modding older pedals to improve them, mostly all sound advice, but he clumsily hacks into the boards but almost invariably them up, and then brings them to me to put right

I told him several times not to attempt these mods but give the pedal to me in the first place to save me the time and effort trying to put his Frankenstein hacks right!
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Old 9th Jan 2019, 7:10 pm   #7
Jon_G4MDC
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Default Re: MN3007 BBD chip

He does all this wearing his ESD wrist strap and sandals of course...
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Old 14th Jan 2019, 5:43 pm   #8
boxdoctor
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Default Re: MN3007 BBD chip

Thanks for the reply, ITAM805. As I said, I have not had much trouble with these, or for that matter most Jap musical instrument chips.
I guess I have just been lucky, maybe.
Re your post #6, I also had a "Mod Maniac" who knew very little, technically, and kept bringing me stuff he (reluctantly) admitted he had had a "poke around" inside. After he grumbled about the very reasonable charge for fitting a new LSI chip to one of his damaged (by him) keyboards, I suggested forcefully to him he went elsewhere for his damage rectification. Never came back, thank goodness! Tony.
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