SOLVED Madbean total recall

[Phil hodson]

Morning all.

It pains me to post this here as I took my time on this one as I knew it’s a complex built. I was hoping to beat @MichaelW to a build report but we both hit problems at the same time. He got a new board and got it working. I’m persevering with mine thought as I want to know what I have done or not done!

So before I loose my patience and or my mind and start ripping things off the board I thought I would ask around on here. I know there are some very accomplished builders and some total recall experts here!

Firstly I have checked values. Cleaned the board. And started an audio probe.

Going from the main audio schematic it’s all good. I get a squeal on pin 3 of IC3 not sure if that’s an issue.

Audio stopped at C14 so I replaced that and it’s fine now. All the way to D in. After that nothing.

I her audio on pin 3 and 4 of IC6 but no delay at all.

Looking at my voltages everything looks good apart from IC4. I get nothing at all ok the right hand side.

I also get no voltage at pin 7 of IC7. Could this be related to the issue at IC4?

My thoughts is a bridge or issue in the socket for IC4. Before I take it off does this sound like it might be the issue?

Any thoughts and suggestions very very very welcome!

See attached pics. Can take more as required.

Phil

 

[zgrav]

The build docs has -7.4 on pins 5,6 and 7. Mine are 0.

see if any or all of those pins are showing continuity to ground. you want to know if voltage might be grounding from that point. if no connection to ground. voltage might not be reaching those pins.

 

[Phil hodson]

@zgrav

IC6 pin 1 ground
IC7 pin 1 ground
IC4 pin 8 ground

no other ground continuity on those ICs

 

[zgrav]

I would pull all of the 4558 ICs and take voltage readings for the sockets to see if you are getting any power to IC4 (but also to see what you get elsewhere). It seems like you have confirmed ground continuity for all of those chips, but confirm that is the case. If you are getting voltage to the socket for IC4, II would also keep track of which chip you are using for IC4 and sub in a different one if you have it.

 

[jimilee]

I don’t want to side track you, but does IC7 pin 7 have continuity with IC 6 pin7? They are connected.

 

[Phil hodson]

Ok. So as suggested I re checked the voltages and as you can see they are wildly different than before. As suggested could this be a dodgy R57 as it’s getting too hot to touch or a dodgy voltage reg which isn’t giving anywhere near what it used to or what it’s supposed to.
See pic for new voltages.

For @jimilee question I don’t have continuity between IC7 pin 7 and IC6 pin 7. Where are they connected? I can’t see that on the schematic.

I have continuity between IC4 pin 7 and IC7 pin 7.

Should I sort out the voltages first then move onto the other issues.

I’m guessing that R57 has to be a 1W because of the 24v coming in. If mine is getting hot it’s first in line to the power. Maybe that’s an issue.

Phil

 

[jimilee]

Hi Phil, I was looking at the shot of the board Brian always puts in the build doc.

 

[Phil hodson]

Hi @jimilee This one attached? How are they connected?

 

[music6000]

Hi Phil, I was looking at the shot of the board Brian always puts in the build doc.

I darken & blew it up at the onset of this discussion.
He was getting all the correct voltages except IC7 Pin 7 & IC4, Pins 5, 6, & 7
Continuity Tests show all traces are good & no bridging with IC4 with Op Amp removed, has tried multiple 4558's!
It apears he is losing voltage via BIAS 2
The current dilemma is R57 got HOT & now he has lost voltage.

Phil H, Can you lift R57 left leg closest to Regulator side & see the Voltage reading?

 

[Phil hodson]

Hi @music6000

So I lifted the R57 leg closest to the reg. I’m getting -32.89 out of the power supply now. -31.89 at the back of the DC Jack.
-32.90 on the +/- points on the board.
-32.85 on the right hand side of R57.
-32.80 on the left of the resistor (lifted side)

No other voltages on the board that I could find.

I left the power on for 30 mins and the resistor didn’t get hot to the touch at all.

What’s next I have spare 240 ohm resistors and also spare LM7915 voltage regs.

 

[jimilee]

Hi @jimilee This one attached? How are they connected?

Cause I meant pin 6, I lost my mind for a minute there.

 

[music6000]

Hi @music6000

So I lifted the R57 leg closest to the reg. I’m getting -32.89 out of the power supply now. -31.89 at the back of the DC Jack.
-32.90 on the +/- points on the board.
-32.85 on the right hand side of R57.
-32.80 on the left of the resistor (lifted side)

No other voltages on the board that I could find.

I left the power on for 30 mins and the resistor didn’t get hot to the touch at all.

What’s next I have spare 240 ohm resistors and also spare LM7915 voltage regs.

Why are you getting 32v, it's suppose to be a 24v - 100ma DC Power Supply?
I would say it has fried the Regulator??

 

[Phil hodson]

Mornng all! Back at it again this morning!

don't worry @jimilee im beginning to feel the same about this pedal haha1 And yes I do have continuity between pin 6 and 6 on IC6 and IC7!

@music6000 yes that is rather high but if you look at the mad bean voltages. The power supply with out a load is giving -34.68 so im close to that.

Moving on, I removed R57 just in case and the voltage reg.

I found something interesting that maybe an issue!

My voltage reg is an L7915CV. The build doc calls for an LM7915. The closest I can find is an LM7915CT.

They are pretty close but in looking at the data sheets, the L7915CV has an Output voltage of -15V, Input voltage min -17.5V and Input max voltage of -35V.

The LM7915CT has in Output voltage of -15V, Input min of -30V and Input max of -7V.

So there is a discrepancy between the two types. Im going to hold off on putting another L7915 in to the pedal unless someone can say its ok to use. I can order another one and try it again soon once it arrives. Could it be that this has been the issue all along!??

Thoughts........

 

[music6000]

MichaelW used the same brand as you, ST LM7915CV?

 

[Phil hodson]

Ok I just looked his up and you’re correct it’s the same model.
His says GK163 Vb, CHN 922

Mine says GK1F5, CHN 106

I dont this makes any difference though.

So should I continue on with it??

 

[music6000]

MichaelW just confirmed with me that 32v is normal with No Load.
Change out the R57- 240ohm & see if you get your voltages back on the Opamp's.

 

[Phil hodson]

And put a new voltage reg in too?

 

[music6000]

And put a new voltage reg in too?

Not yet, I want you tou tomeasure Voltage coming from the Regulator OUT (Top Pin).

 

[MichaelW]

Ok I just looked his up and you’re correct it’s the same model.
His says GK163 Vb, CHN 922

Mine says GK1F5, CHN 106

I dont this makes any difference though.

So should I continue on with it??

If you were getting ~-15v at the output of the regulator then it's unlikely that's the problem. I'll have to check and see which reg I used, I have some different ones but I've always used them interchangeably with no issues. If you're getting -15v at the reg then everything else is getting power downstream of that and it's probably not the issue. Also, as I recall, (see what I did there) you're getting plenty of clean signal and your gain pot is working correctly right? (Like mine that didn't work). So again, not likely it's the regulator.

 

[MichaelW]

The only thing I did not check on my failed build before giving up was underneath the sockets to see if there wasn't a solder blob or something. But then I'd probably destroy the board removing the sockets......

 

[music6000]

Not yet, I want you tou tomeasure Voltage coming from the Regulator OUT (Top Pin).

Check what Voltage you get at these 3 Highlighted Circles @ R60, R45 & BIAS 2 Leg 3 :