e-licktronic Forum

I am building the Yocto, section by section, right now. I just finished building the Cymball and I am seeing only +13.9V and -14.4V on U5. This is about a half-volt less than I have been seeing when testing op-amp pads in other sections.

Can someone advise how to bug-chase the dropped voltage on this section? I'm not sure where to begin looking for the source of the issue.

Thanks so much for considering!

I just finished building the Cymball and I am seeing only +13.9V and -14.4V on U5. This is about a half-volt less than I have been seeing when testing op-amp pads in other sections.

Have a look at the schematic please:

1. Did the Voltage on U3 check out fine?
I'm also curious what Voltage you measure on the Positive sides of R86*, R96* and R102*?
(They're all on the same positive rail as pin8 of U5 named +B1*)

2. When you measure pin8 of U5, where do you put the probe? On the pcb, a socket or with the ic soldered in?

3. Is the Voltage on U1 still like expected??

Hi, ikke

I finished the build and everything sounds good EXCEPT the Low Tom, which doesn't sound at all.

I have tried everything from resoldering every point to replacing the 4558 and diodes. I see normal voltage across the 4558.

THANK YOU SO MUCH!!!

ikke wrote:

I just finished building the Cymball and I am seeing only +13.9V and -14.4V on U5. This is about a half-volt less than I have been seeing when testing op-amp pads in other sections.

Have a look at the schematic please:

1. Did the Voltage on U3 check out fine?
I'm also curious what Voltage you measure on the Positive sides of R86*, R96* and R102*?
(They're all on the same positive rail as pin8 of U5 named +B1*)

2. When you measure pin8 of U5, where do you put the probe? On the pcb, a socket or with the ic soldered in?

3. Is the Voltage on U1 still like expected??

Good to see you got it sorted out!
So all the instruments (except for the Low Tom) work like they should despite the weird voltage drop on the 4558's?

[/quote]Have a look at the schematic please:

1. Did the Voltage on U3 check out fine?
I'm also curious what Voltage you measure on the Positive sides of R86*, R96* and R102*?
(They're all on the same positive rail as pin8 of U5 named +B1*)

2. When you measure pin8 of U5, where do you put the probe? On the pcb, a socket or with the ic soldered in?

3. Is the Voltage on U1 still like expected??[/quote]

Hey, I'm having a similar problem whereby i'm reading 14.1V + & - in their respective places on the two pins of U5. I have checked the resistors you mentioned, all show 14.1V+.
I am probing on the PCB, no socket or IC installed.
The only significant voltage I am reading on U1 is a perfect 5V+.

Hey Jeremy,
I think it has something to do with the R/C's on the powerlines and their tolerances.

You could have a look at R165*, C85* for the 15V+ line and R164*,C84 on the 15V- line and see how big the input voltage and voltage drop is and compare them to for instance +/- B2.

It also depends a bit what Voltage you get from the I/O board I believe so you have to take that in account. It's only a 1% out of tolerance on top of the 5% so... You'll probably be fine.

But that could also be caused by a flaky multimeter. I have had some little variations in my measurements aswell, but like in the range of +/- 0,15V.

Keep in mind I'm no expert by far either.