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

 

[Feral Feline]

... The audio on pin 3 is quieter than pin 3 ...

Please clarify.

I've been looking at the schematic and your notes about the problem area etc, but there are people here far better at troubleshooting than me, so this is just a BUMP! Hope some geniuses weigh in soon and you get this thing sorted.

 

[Phil hodson]

Please clarify.

I've been looking at the schematic and your notes about the problem area etc, but there are people here far better at troubleshooting than me, so this is just a BUMP! Hope some geniuses weigh in soon and you get this thing sorted.

On IC3 pin 1 and 3 the audio is quieter than other points on the board and other IC’s. And Pin 2 gives a squeal. Maybe because it’s going to ground??

Thanks for the bump Neil. I need it! Going around in circles with this one.

Would love to get it sorted as everyone raves about theirs.

Phil

 

[music6000]

On IC3 pin 1 and 3 the audio is quieter than other points on the board and other IC’s. And Pin 2 gives a squeal. Maybe because it’s going to ground??

Thanks for the bump Neil. I need it! Going around in circles with this one.

Would love to get it sorted as everyone raves about theirs.

Phil

I thought this may help with Continuity Test on IC4 Right side:

 

[Phil hodson]

I thought this may help with Continuity Test on IC4 Right side:

View attachment 43848

Wow that’s for that. This is exactly the sort of thing that helps. I have been following the audio schematic from the build diagram which has been really helpful too.
I who’ll check out those points again today and see what I get.

Thanks.

 

[Phil hodson]

So, @music6000

From the bottom up. I have continuity from R44 to gain 1 and pin 6 on IC4

I have continuity from pin 5 IC5 to bias 2.

I have continuity from pin 7 on IC4 to pin 7 on IC7 and R46.

I have continuity from pin 8 IC7 to bias 2

And finally I have continuity from R46 to Gain 1

 

[jimilee]

Is c35 bipolar? It’s hard to tell from the picture.

 

[Phil hodson]

Hi @jimilee

Yes sir it is. 2.2Uf NP 50v.

 

[music6000]

So, @music6000

From the bottom up. I have continuity from R44 to gain 1 and pin 6 on IC4

I have continuity from pin 5 IC5 to bias 2.

I have continuity from pin 7 on IC4 to pin 7 on IC7 and R46.

I have continuity from pin 8 IC7 to bias 2

And finally I have continuity from R46 to Gain 1

Confirming Continuity test has to be with No power connected:
Have you pulled IC4 out & tested for Continuity between 8 & 7, 7 & 6, 6 & 5.... 4 & 3, 3 & 2, 2 & 1
What Voltage are you getting @ Pin 8?

 

[Phil hodson]

Hi @music6000

All continuity checks were done with no power connected.

I just pulled the chip and checked the pins. I have no continuity between any of IC4 pins and each other.

I’m getting 0v on IC4 pins 5,6,7 and 8.

On another note while I was just testing this I could “smell” heat. I touched the chips and they are all fine and I tracked it down to the big 1W 240ohm resistor. Which was extremely hot to the touch. Why would this get so hot? Is the capacitor next to it going to be ok if this is getting hot?

Just to double check I have attached pics of the power supply. Is this wired correctly??

I’m using an original electro harmonix 24v power supply.

Thoughts??….

 

[Coda]

Can that circuit run at 24v? Maybe I’m thinking about the Current Lover…

 

[Phil hodson]

Yep this one too. Although it is a positive ground.

 

[music6000]

I thought this may help with Continuity Test on IC4 Right side:

1. What Voltage are you getting on BIAS 2 / Leg 3 green pad ie -15.28v?
...
2. What Voltage are you getting on BIAS 2 / Leg 2 purple pink dot & can you get -7.45v by rotating Bias 2 trimmer?

 

[Phil hodson]

ok @music6000

I get -1.1v on leg 3 of bias 2

And the range of pin 2 bias 2 goes from 0.5v to -1v at its max. No where near -7.5!

 

[music6000]

ok @music6000

I get -1.1v on leg 3 of bias 2

And the range of pin 2 bias 2 goes from 0.5v to -1v at its max. No where near -7.5!

You showed that you are getting -15.28v on IC7 / Pin 8 which is connected to BIAS 2 / Leg 3, is that correct?

 

[Phil hodson]

@music6000

That was correct. Now I’m not. And not at pin 8 on Ic6 either.
I went back to the start and am getting -24.6 in. So a bit lower than before. I’m getting 24.6 going into R57 and -6.6 out.
I am also only getting 6.6v on both the I and O of the voltage reg could this be a power issue now too?

 

[music6000]

@music6000

That was correct. Now I’m not. And not at pin 8 on Ic6 either.
I went back to the start and am getting -24.6 in. So a bit lower than before. I’m getting 24.6 going into R57 and -6.6 out.
I am also only getting 6.6v on both the I and O of the voltage reg could this be a power issue now too?

R57 getting Hot is a concern, wondering if the Voltage regulator is faulty?

 

[music6000]

R57 getting Hot is a concern, wondering if the Voltage regulator is faulty?

Can you lift the left leg on R57- 240 ohm & see if your voltage returns or if the resistor has died/dying?

 

[zgrav]

I still have absolutely no voltages on pin 5 to pin 8 on IC4!

Is this still correct? Have you checked to see if any of those pins are connecting to ground?

 

[Phil hodson]

Can you lift the left leg on R57- 240 ohm & see if your voltage returns or if the resistor has died/dying?

the leg closest to the voltage reg?

 

[Phil hodson]

I still have absolutely no voltages on pin 5 to pin 8 on IC4!

Is this still correct? Have you checked to see if any of those pins are connecting to ground?

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