Shunt regulator board

[triode]

Hi

I tried to upgrade my extended FPIII coupling caps, but somehow my clumsy hand bend something in the shunt regulator board.

When I turn it on, I got a spark and the 2.45k resistor end up fried. Looks like the 147k resistor wire touching the 2N2907 metal enclosure. I think I need to rebuild the board.

Do anyone still have a spare unused/board for FPIII? are they still available?

Thank you for your help
Regards

[Paul Birkeland]

These are very much NLA.  I do repair these preamps and I put in one of our newer PC boards that's physically a lot larger but fits just fine with longer standoffs.  There is no documentation on how to do this and the demand is low enough that I can see that being offered in the future.

It is also possible with a powered desoldering tool to simply suck the solder out of all the eyelets on the board and replace what you need to. 

[triode]

Thanks Paul

I will try to replace the component first. If fail, maybe I will get the new version/bigger board

Should I replace just the 2.49k resistor? or also the 2N2907 and other more? how I can test?
Also I assume the other section (the A side) should be still OK?

Thanks for your help

[Paul Birkeland]

On that center board, the MJE350s should be replaced with MJE5731As if they haven't already (which face the opposite way).

I would then test the rest of the components with your meter set to continuity beep.  Typically a transistor that fails will show a short between a pair of legs, then you know it's toasted.

[triode]

Hi Paul,

I think I will need to get a new board.
Would the board from Monamour works? I can work out how to populate the board by comparing the schematics

I know its a bit wider than the original board. Maybe I also need to change the C4S for the L/R channel to slim one like the one use for SEX 3.0?

Thanks

 

[Paul Birkeland]

As I said before, we don't keep a manual or instructions around on how to do this.  The Stereomour II shunt regulator upgrade kit would get you the board and solid state parts you need without the Foreplay resistors and without the correct standoffs to make it fit (please do not order this kit and ask for the resistors to be left off though, as this creates a substantial amount of extra work and we will not provide a discount for leaving these parts off).

Beyond that you will have to figure out how to populate the board and install the jumpers in an identical way to get things up and running, as well as performing the debugging if things don't end up working quite right. 

[triode]

Thanks Paul,

I will try to figure it and work it out. I think it also similar to Side B of Monamour board with different resistors?
Maybe I can just get the board and get the components from Mouser

Will contact Eileen

Thanks

[Paul Birkeland]

The Stereomour shunt regulator kit will cover everything but the resistors including heatsinks, transistors, the board, LEDs, etc.  It also has the correct parts population and the correct wire jumpers that you'd want, so the instructions are close but you need to change the values of a few resistors to get things right.

[triode]

Paul

I just realise that this sparks its because I plug the 110V Foreplay to 240V line !!!
Apart from obvious damage in shunt regulator board, would this also cause problem in the C4S boards or power supply?
I only plug it a few second and unplug quickly due to the spark in shunt regulator board.

Thanks for your help

[Paul Birkeland]

You may have damaged the power transformer and every single electrolytic capacitor in the Foreplay, and you've given the tubes 12V of heater voltage where they were expecting 6.3V.  Frequently when something like this occurs repair is not possible.

[triode]

Thanks Paul

I will try and test, and hope for the best.
The resistance check seems ok, no shorts in power transformer and caps, but maybe thats says nothing.

Regards

[Paul Joppa]

Inspect every electrolytic capacitor for possible bulging. You can check resistance of the  heaters on each tube, to see if any are blown out. Check the fuse.

PB is on vacation, but should be back in a few days.

[triode]

Thanks PJ

Checked and no shorts and no bulging caps. Phew.
Also managed to check for the DC output at last caps in PS and show 190VDC (with no load).
I guess I got away with murder...
Will install the new shunt regulator board

Thanks again

[triode]

All fixed!!!
Installed the board and worked fine
Making music as good as ever, even better.
I think the Jupiter caps really good. Here's a picture of bottom side

Thank you PB and PJ