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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets. |
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1st Jan 2019, 2:46 pm | #1 |
Nonode
Join Date: Jul 2010
Location: Folkestone, Kent, UK.
Posts: 2,172
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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 |
1st Jan 2019, 3:35 pm | #2 |
Heptode
Join Date: Mar 2011
Location: Dorset, UK.
Posts: 519
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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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To an optimist a glass is half full; a pessimist half empty; an engineer twice as big as need be! |
1st Jan 2019, 8:54 pm | #3 |
Nonode
Join Date: Jul 2010
Location: Folkestone, Kent, UK.
Posts: 2,172
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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 |
6th Jan 2019, 10:13 pm | #4 |
Nonode
Join Date: Jul 2010
Location: Folkestone, Kent, UK.
Posts: 2,172
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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 |
9th Jan 2019, 11:50 am | #5 |
Rest in Peace
Join Date: Sep 2010
Location: Ripley, Derbyshire, UK.
Posts: 785
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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. |
9th Jan 2019, 12:36 pm | #6 |
Nonode
Join Date: Jul 2010
Location: Folkestone, Kent, UK.
Posts: 2,172
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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! |
9th Jan 2019, 7:10 pm | #7 |
Nonode
Join Date: Nov 2015
Location: Welwyn Garden City, Hertfordshire, UK.
Posts: 2,013
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Re: MN3007 BBD chip
He does all this wearing his ESD wrist strap and sandals of course...
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14th Jan 2019, 5:43 pm | #8 |
Rest in Peace
Join Date: Sep 2010
Location: Ripley, Derbyshire, UK.
Posts: 785
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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. |