Kaiju build problem [resolved]

[Lr1001]

Hello.  Started my Kaiju build.  Got some experience with the Beepre and stereomour.  I went through the build process and got to the voltage testing for the circuit boards--specifically, the right side, A c4s.  I did a 2 voltages tests with proper IA and OA voltages measured 530/300--the leds glowed, no problems etc. I adjusted the pot to 175vdc.   On a third power up, maybe a minute into the warmup, there was a dramatic "pop"-R1 resistor blew (see pics).  I am a little stumped and would like to get some input on how to proceed.  I am assuming that the R1 resistor and adjacent PM transistor needs to be replaced.  I guess the board should be replaced and just build a new one.   Thanks.

[Paul Birkeland]

My best guess is that if you flip over the board, something will be touching one end of that resistor that shouldn't be.  The most likely culprit would be a black jumper that perhaps got pressed into one of the cut ends of that resistor.

I also feel like I did this to one of Clark Blumenstien's Paramounts some years ago, and the issue ended up being a jumper that wasn't well connected.

[Lr1001]

Thanks for the input.  I did desolder some of the jumpers, to free up the board for inspection.  The black 1U/-reg jumper was brittle/broke with very little manipulation at the 1U solder point.  So maybe that's it.   I inspected the traces and soldering points without evidence of "short" to explain the overload to the resistor.  pics included.  Again, everything tested fine on the right side, I moved to the left, and it popped.   Doesn't fit with my other board work on the various projects.  It will probably worth changing out the resistor and PN transistor and see what happens.

[Paul Birkeland]

It also looks like you have at least one toasted LED on the A side as well. 

I would imagine that replacing the resistor, LEDs, PN2907, and MJE5731A will get you up and running. 

[Lr1001]

Well, I have investigated the extent of the blown circuit.  The damage extends from IA including pn and mje npn transistors, 2 led's, and blown 90.0ohm resistor carrying down into the 5 zener shunt diodes.  Everything else on the board-B side heater/tube seems to be in good shape.  I was able to test on the Left channel to ensure the 5670 is fine.  So, just replacing some cheap parts.  No obvious explanation--short or bad wiring.  Again, the circuit had been tested per the manual and working fine up until a third test and sudden light show before final assembly and testing. 

[Paul Birkeland]

Can you post a photo of your zener string?  Zener string issues can cause similar damage to this as well.

[Lr1001]

I pulled the zener diodes after I tested the bias/continuity, all bad-open, but no apparent physical damage.  When I was desoldering them two basically crumbled.  Interesting...and fortunate for the rest of the components.

[Lr1001]

update:  definitely applied too much heat to the min led's on the pcb-500F recommended, station set at 730F.  The miniature led's are fragile and I applied too much heat during the build.  Desolder is best with a dedicated device-hakko 808 when cleaning up the pcb for replacemnt/resolder for the hlmp 6000 leds.  Back on track.

[Paul Birkeland]

FWIW, I have my soldering station set to 899 degrees F and haven't done any damage.  The bigger issue with those diodes is not heating them for very long. 

[Doc B.]

Yup, they are more likely to be damaged by being moved around after they are soldered. Sometimes too low a tip temp means a longer dwell time on the work, which actually allows the high temp to soak farther up the lead than it might from a quick hit with a really hot tip. It's more of a technique thing than a temp thing. Most full time techs I know run their stations at max temp most of the time to minimize the dwell time.

[Lr1001]

Replaced a c4s board, tested with beepree and jaegers.  Sounded great.  Installed the dc filament kit.  Even better.  The kaiju really brings out the range and depth of the jaegers.  Super happy with outcome. Thanks.