Megavibe Reverse Engineering (PICS Included)

harkkam · Post by **harkkam** » 28 Jan 2011, 20:02

Hey guys I am trying to reverse engineer my megavibe.

I have the board layout, all resistors and capacitors used.

What I dont know are some of the transistors because it looks like the builder etched them out so we could not replicate it.

Nor Do I know which LDR is being used. But I have gut shot pictures maybe people can help me out.

harkkam · Post by **harkkam** » 28 Jan 2011, 20:04

more pics included

harkkam · Post by **harkkam** » 28 Jan 2011, 20:22

I measured the resistance of the photocell it ranges from 5.5k when fully exposed and 5.8k when covered with a finger

harkkam · Post by **harkkam** » 28 Jan 2011, 20:26

harkkam wrote:I measured the resistance of the photocell it ranges from 5.5k when fully exposed and 5.8k when covered with a finger

I am double checking however as this does not seem right.

culturejam · Post by **culturejam** » 28 Jan 2011, 20:40

harkkam wrote:Nor Do I know which LDR is being used. But I have gut shot pictures maybe people can help me out.

Aren't they all used in a vibe?

harkkam wrote:I measured the resistance of the photocell it ranges from 5.5k when fully exposed and 5.8k when covered with a finger

I think you'd need to remove them from the circuit to get an accurate reading.

harkkam · Post by **harkkam** » 28 Jan 2011, 20:41

To me it seems it is a CDs and I remeasured the resistance it has 4.8k when fully exposed to light and 65k when totally covered.

harkkam · Post by **harkkam** » 28 Jan 2011, 20:43

I used the one closer to the bulb that has leads sticking out of it. SO that made it easier and I didnt have to pull one out

harkkam · Post by **harkkam** » 28 Jan 2011, 20:51

After doing some more testing I realized that I was not fully covering the LDR. Now I put some black electrical tape over one of them to get the proper reading.

When fully exposed its 4.5k-5k and when totally covered it is 1.7M to 1.8M

Hides-His-Eyes · Post by **Hides-His-Eyes** » 28 Jan 2011, 20:56

How the fuck is he using so much solder to build these?

harkkam · Post by **harkkam** » 28 Jan 2011, 20:59

I covered it some more and now it reads 37M at darkness. What is a good way to measure it?

madbean · Post by **madbean** » 28 Jan 2011, 21:03

Yeah, his solder budget must be pretty high. A little over the top!

Interesting that there are 5 photocells. More interesting where #5 is located.

I wouldn't worry too much about the actual transistor type used. I would see if you can figure out what pinouts they are, though. That would help narrow it down.

harkkam · Post by **harkkam** » 28 Jan 2011, 21:10

I am going to speculate that it is 5k to 2M.

harkkam · Post by **harkkam** » 28 Jan 2011, 21:11

Pinouts as in which one IS the base collector emitter?

mcaviel · Post by **mcaviel** » 28 Jan 2011, 23:26

harkkam wrote:Pinouts as in which one IS the base collector emitter?

Yep.
Also every time i see the solder work on this pedal i goes like this

sinner · Post by **sinner** » 28 Jan 2011, 23:30

mcaviel wrote:
harkkam wrote:Pinouts as in which one IS the base collector emitter?
Yep.
Also every time i see the solder work on this pedal i goes like this

I do the same when I'm looking into any vintage EHX pedal, but that doesn't change the fact that those are fine sounding units

culturejam · Post by **culturejam** » 29 Jan 2011, 01:51

harkkam wrote:Pinouts as in which one IS the base collector emitter?

I would just desolder one of them and measure it. Of course, that would take half an hour on this pedal.

harkkam · Post by **harkkam** » 29 Jan 2011, 04:30

Okay so I figured out that it is a NPN transistor

THat has a pinout reading of E-C-B

the base is not in the middle.

I used this method to test it

http://www.allaboutcircuits.com/vol_3/chpt_4/3.html

Very well written.

Would I need the gain reading to be able to find a good substitute?

harkkam · Post by **harkkam** » 29 Jan 2011, 04:52

I think this might be the tranny that is being used.

I think it is a BC183L.

http://www.datasheetcatalog.org/datashe ... Xuvyzv.pdf

solder_blob · Post by **solder_blob** » 29 Jan 2011, 07:37

What are the values on the trimpots?

harkkam · Post by **harkkam** » 29 Jan 2011, 07:40

its a piher 200 ohm trimpot. Only one of it turned all the way up