EROS 2 shunt regulator error [resolved]

[MisterM]

My EROS 2 build went perfect until I mixed up the 220 ohm and 220 K ohm resistors on the shunt regulator bd. Didn't find out until I ran the power on check. All four LED's lit but voltage on the MJE5731A tab was 18 vdc. I immediately shut down and replaced the resistors with correct new ones. Upon the power on check no LED's were lit and voltage on the MJE5731A tab was 363 vdc. What did I fry? Triple checked all other components and wire connections and all are correct. I also installed the 100 k ohm 3W resistors at R2 on the A and B side of the board as pictured even though the instruction listed only the B side, was I wrong?

 

[Paul Birkeland]

Yes, the 100K resistors go on both sides.  Thanks for pointing that out, I forwarded it along to get the manual ammended.

What are the Kreg voltages on that board?  Putting in 220 ohm resistors in place of 220,000 ohm ones will put a ton of stress on the 431 regulators, so they may have self destructed.

 

[MisterM]

Kreg A side is O vdc and B side is 1.26 vdc so I must have fried the 431's. I have every part on that board in my parts stash except those 431's Drat!!

 

[Paul Birkeland]

Yeah, I would just toss those.  Also you can set your meter to beep for continuity and just check that the MJE5731A and PN2907 transistors are OK by being sure that no pair of legs reads as shorted together.  The C4S should tolerate that error reasonably well far longer than the 431s will.

 

[MisterM]

Thanx for the quick response. MJE5731A and PN 2907 A side shorted, B side not. Since I got 'em I'll replace all and try to find some 431's.

 

[Paul Birkeland]

When there's that kind of damage, I would also go ahead and use the diode checker on your meter to check the LEDs.  Sometimes when the LEDs get taken out, they explode, but sometimes they to not. 

Your checker should show about 1.5V with the probes in one direction and will likely light the LED up, but nothing in the other direction.

 

[MisterM]

Replaced all transistors and diodes on the shunt regulator board. All tests were passed with flying colors. Finished build and all resistances and voltages were correct. Have been listening to LP's all afternoon, thanks Bottlehead for a great sounding amp.  UNFORTUNATELY my solder station gave its life during this project and I finished up using my ancient (45 y. o.) Unger 35W soldering pencil. Now to find another soldering station.

 

[Paul Birkeland]

I'm glad it all went back together well.

I've been happy with the Hakko 888, though it's a little weird to adjust the temperature.