Dropped my Reduction :( [resolved]

[Mesz77]

Hello all,

Recently I dropped my reduction preamp. It's been working just fine for about a year. I was messing with some spiked feet that I put on it, and I tilted it just a little too much. The board came out and the underside with all the components landed on a table. Unfortunately, it isn't working properly. I have the integration upgrade installed so the three circuit boards took most of the force along with the three electrolytic capacitors in the power supply. The circuit boards themselves dont look damaged, but some of the transistors got bent. These bent transistors include the two MJE5731 ones on the center circuit board and two of the MJE250 ones in the right channel. The left channel (I believe, it's the one with black rca jacks) LEDs are lighting up including the circuit board above it. However, all of the right channel LEDs AND the LEDs on the center circuit board are not lighting up at all. I resoldered the three capacitors in the power supply and the two MJE5731 transistors on the center circuit board to no avail. Any help is much appreciated because I am quite distressed and sad right now.

 

[Paul Birkeland]

Start with a voltage check.

 

[Mesz77]

Alright PB,

I did some voltage checks on every terminal and the two MJE5731 Transistors. Here are the ones that were off with their readings:

Terminals 2,7,13,14,15: 0.5V
Terminal 4: 1.5V
Terminal 29: 165V
Terminals 50,51,59,60: 175V
Terminals 56,57: 168V

One MJE5731 transistor read 163V and the other read 1.5V

 

[Paul Birkeland]

I'd post some photos of the build as it sits now.

 

[Mesz77]

Let me know if you need photos of anything specific:

 

[Paul Birkeland]

On the center upper board on the side reading 1.5V, slip the red teflon wire out of the board (it will be connected to OA or OB).

Remeasure the metal tab on that transistor and see if it stays at 1.5V or pops up to ~100V.

 

[Mesz77]

It jumped up to about 11.7V

Edit: It started at 11.7V but is climbing at about 0.1V a second
Edit 2: It's still climbing after about 5 min but at a much slower pace. It's around 32V now

 

[Paul Birkeland]

Flip that center board over and resolder every joint on it. 

 

[Mesz77]

I resoldered every part on the center board and the board above terminals 1-16. Every LED on all three boards are lit up now. Here are the new readings:

Terminals 2,7,13,14,15: 70V
Terminal 4: 107.5V
Terminal 29: 108.5V
Terminals 50,51,59,60: 156V
Terminals 56,57: 136V

Both MJE5731 Transistors are at 106V

 

[Paul Birkeland]

So it looks like you've resolved your issue.

 

[Mesz77]

That's very good news to hear! I just want to double check though because some of the voltages are off from the manual:

Terminals 4 and 29 are around 108V but it says it should be around 145-155V
And Terminals 50,51,56,57,59,60 are all about 10V lower than the manual says

 

[Paul Birkeland]

Integration changes the voltages at 4 and 29 (that's the high voltage regulator at work).

The lower voltages at the other terminals reflect some extra current being drawn by the Integration to perform the regulation.

 

[Mesz77]

Alrighty then. Thank you so much!