Shunt Regulator Voltage Issue

[Art Andrews]

I am on page 58 of the manual and am testing the Shunt Regulator voltage.

I get the expected 300 and drop to ~225 on the red line from D1. However, on the red line from D6 I get 300 and then a drop to about ~148-140. I have revisited all the wiring but simply do not see my error. Any thoughts?

[hmbscott]

Looking at the instructions for making that measurement (Pg 55 of my Eros II manual), it says measure from ground post to metal tab of each MJE5731A. Why are you measuring from D1 and D6 to ... ?

[Paul Birkeland]

If the 2N2907 transistors are installed against the PC board, that can cause problems. 

There are some solder joints on the PC board that also don't look 100% flowed out. 

What are your Kreg voltages?

Typically the 148V indicates unrestricted current passing to that half of the D socket, and often that is a solder bridge on the bottom side of the PC board.

[Art Andrews]

Hi Paul,

I have detached and pulled the 2N2907 transistors up ever so slightly so they aren't sitting on the board. It is very slight but they are off it now. I also went back and tried to resolder everything and check everything. Same results.

I unsoldered a few wires to access the bottom of the board. Here is where I currently stand.

I don't know how to take Kreg Voltages. If you could assist me on what is needed, I am happy to get them.

[Paul Birkeland]

Is there lead in your solder?  Is your soldering iron turned all the way up?

[Art Andrews]

Hi Paul,

My solder gun is set to 750.

I am using Cardas Soldering Wire, which is "a blend of silver, copper, tin and lead." I was told this was quality solder for this type of project and used this same solder on my mailnine which turned out great.

It would be painful, but I could go back and unsolder everything on that board and resolder it if necessary. Or, if there are specific items you think I need to detach and reattach, I am happy to do it.

[Paul Birkeland]

I would just turn your iron (hopefully not a solder gun) as high as it will go, as those joints will flow out a bit better with a hotter iron.  You can reheat all the joints except the LEDs on that board and it may help.

[Art Andrews]

Hi Paul,

I misspoke when saying soldering gun. I have a Weller 70 watt soldering station. I believe I can get it up to 850 but I thought for boards, you were supposed to stay between 650 and 750. Will go back through at the higher temp and reheat all the joints. Given the meter reading is the issue limited to the board itself, or might there be issues elsewhere that I need to also look at?

I'd still love to get you those KREG readings, but not sure where I am placing the negative.

[Paul Birkeland]

The negative always goes to ground for DC voltage readings.

[Art Andrews]

Using this photo as a guide, the KREG on the left reads 0.5 and the KREG on the right reads 5.95.

[Paul Birkeland]

What's the voltage on the +275V pad on the power supply board when you see the regulated voltage dip down to 150V?

[Art Andrews]

0.8.

Is that right?

[Paul Birkeland]

You may be measuring the - pad, which would be around 0, but it would be helpful to know what's present on the + pad.

[Art Andrews]

Don't know what I was doing before, but clearly off-base.

293v on the + side.

[Paul Birkeland]

I would double check the resistance values of the R1 resistors on the C4S board to be sure they are correct.  Also be sure that the correct part is installed in the 431 position.