SSR03 24v build problems

[PJN]

Hi Peranders,

I have just completed a 24v build of the SSR03 using the LM431 BOM. I am using an Antek 100 VA 35v toroidal transformer to power the psu. The positive side appears to work fine, I'm reading 35.4 vdc at X2 and getting 23.7 vdc at +VOUT. On the negative side I'm getting some crazy readings and I'm a bit confused. I'm reading -7.6 vdc at X2 and 4.8 vdc at -VOUT. The AC in to the PSU is 36 vac. Seems like something is wrong in the rectifying section, maybe bad diodes. I have included a picture of the build for your review. I'd appreciate any advice of where to look.

Many thanks,

Paul

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[peranders]

What is you AC voltage at X1, 3 and X1,4?

Resistor value of R3, R4 and R10?

Voltage across C8?

When you have the board unpowered, do a diode test with your multimeter?

[PJN]

Hi Peranders.

Ac voltages at X1,3 = 14.68 vac,  X1,4 = 35.77 vac

Resistor values as measured on the board R3 = 2.3R, R4 = 2.3R, R10 = 2.3R

Voltage across C8 = 7.76 vdc

Diode test with board unpowered on D1, D2, D3, D4 all returned 0.55

I have attached a pic of the trafo wiring hookup, I'm uncertain if this is correct being that the input looks to be for a centertapped hookup.

Paul

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[peranders]

Where is you center tap connected? Your transformer seems not to have a center tap, unusual for toroidal. Do you have a datasheet of the transformer?

[PJN]

I have attached the data sheet. To configure as centertapped I would need to tie the blue together to serve as ground then the two greens would go to AC1 and AC2. I can try this hookup.

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[PJN]

Opps, my transformer is 36 v, same wiring layout though.

[peranders]

You have two separate windings as usual but unfortunate the voltage is a bit high. 2 x 24 VAC is good for 24 VDC out. 32 V AC will create maybe 34 * 1.4 = 47-48 VDC when it's rectified and smoothed. You are saying that you have a 36 V type and this will lead to 53 VDC. Not good....

Anyway, the correct connection is:

Winding 1, green => X1, 1
Winding 1, blue => X1, 2
Winding 2, green => X1, 3
Winding 2, blue => X1, 4

[PJN]

Thanks for the help, I'll get a 24v trafo and hook it up

[PJN]

Hi Peranders,

I received the correct transformer today and hooked it up as you directed, here is what I get :

AC in : X1,2 = 24.57 vac,  X3,4 = 24.57 vac

@X1 : -V = -29.14, +V = 31.04 vdc

-Vout = -25.24 vdc

+Vout = 24 vdc

Much, much better. I wonder about the rail mismatch though, do you think that I may have compromised some of the components in the negative regulator when I hooked up the old trafo incorrectly ? Do you have any ideas on what I should change out to get +Vout and -Vout closer in value ? I'm going to use this to power a preamp and I'm worried about a channel imbalance.

Paul

[peranders]

Voltage at the opamps, pin 2 and 3?

[PJN]

Hi Peranders,

I went over the board with a powerful magnifying glass to look for problems, I didn't find anything obvious but did clean up a suspicious long leg on a transistor that was very close to another pad. Then went to take some more readings, what I found was that things had come even closer together. The readings I took are shown in the attached picture. -Vout was -24.38 vdc and +Vout was 23.99 vdc pretty darn close. I left it powered for about 10 minutes, readings were the same and the heat sinks were only slightly warm. I'm guessing the problems due to my sloppy work are solved. Thanks for your help, it is very much appreciated.

Paul

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[peranders]

Good, seems to be working now.