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 Forum index » DIY Hardware and Software » Thomas Henry designs
Soldered in new chip...now LFO doesn't work.:(
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mubase



Joined: Mar 24, 2011
Posts: 110
Location: London UK
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PostPosted: Tue Jan 29, 2013 11:33 am    Post subject: Soldered in new chip...now LFO doesn't work.:(
Subject description: changed the chip for another. Now working except LFO..
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Ive been very busy with Uni work (stifles a semi yawn..theres no electronics this year. our hardware lecturer left and theres a cupboard full of Arduibos not being used Evil or Very Mad )
Also been learning about FPGAs. I've got a Papilio one 500K and a Logicstart board. But about SN-Voice..
I tried everything to get the chip to stay in and couldn't get it to stay.
So I unsoldered the Sdip socket and replaced the chip with a 28 pin dip ( I got it chea from China.
Now I have everything working fine including PWM but now the LFO doesn't work :..(
I've looked around the circuit and can't see anything unconnected.
When I change the LFO Range it makes a small difference and the tone goes down maybe half a semitone but that is all.
Is it possible that DIP packages have a slightly different LFO configuration??
I wouldn't have thought so but... hmmm I am stumped on this one...

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State Machine
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PostPosted: Thu Jan 31, 2013 7:05 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi MuBase

Lets start by having you explain the patch first, then we can zero in on what we think is happening.

Aside from the LF444 buffered/amplified//offset LFOOUT, which buffers the LFORANGE capacitor, there is not much else involved. I know the LFORANGE is also sent to a modulation selector switch via a 4.7M resistor which end up using the LFO to "PWM" the output.

Do you have an oscilloscope?

Thanks
Bill
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mubase



Joined: Mar 24, 2011
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PostPosted: Tue Feb 05, 2013 3:31 pm    Post subject: re LFO Reply with quote  Mark this post and the followings unread

Hi Bill! Sorry I am a bit slow in my responses. Work stops me..
I see pins 20 & 21 of the 76477 connect to LFO. I have an oscilloscope. what should I be looking out for?

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mubase



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PostPosted: Tue Mar 05, 2013 5:00 am    Post subject:  Ready to go to lengths over SN LFO. Reply with quote  Mark this post and the followings unread

Still no joy after coming back to the circuit, changing the 4.7Mohm resistor, checking all junctions connections etc etc. If it comes to it I will build a small LFO circuit to stick on the underside of the face (theres no room anywhere else.) I have another one of the 76477 chips from the same supplier and I have successfully breadboarded a simple VCO/LFO circuit which works fine. Its a mystery.
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mubase



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PostPosted: Fri Mar 15, 2013 10:14 am    Post subject: LFO not woia problem????
Subject description: Could it be a via??
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Hi to everyone.

My SN voice has been sitting exposed for some time now. The LFO stopped working. I have tested as much as I can and have now completely disconnected the board from the module. I would like to know if it might be possible that in changing the 76477 chip, I could've damaged a via associated with the LFO?? Does the LFO have any vias that could be affected??


I'm going to take the chip off the board with a sucker and have a good examine again.....
If you read this Bill or anyone who knows the PCB
outside in, please let me know,
thanks again,
Steve.

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