[SOLVED] Need Help - Extended Foreplay III Upgrade

[Natural Sound]

How are the "O" voltages on the glowing board?

The center leg of the MJE350 and MJE340 is internally heatsinked, often these need a little extra time from the soldering iron.

I'll check the voltages here in a little bit.

What do you mean when you say, "The center leg of the MJE350 and MJE340 is internally heatsinked, often these need a little extra time from the soldering iron."? Does it mean that I should leave the heat on that connection a little longer when soldering?

[Natural Sound]

Hmmm... Not good, the voltages on "O" pads are 48v on the (left) and 31v (right). The LED's do seem a bit brighter now.

BTW, the voltage starts off high ~ 230v and then drops when the tube is on for about 10 seconds or so.

NOTE: The shunt regulator is still bypassed at this point.

[Paul Birkeland]

I'd flip the outside pair of boards over and shoot some more pics.

Yes, my previous comment meant that when your soldering iron touches the center leg of an MJE350 or MJE340, the chip will attempt to dissipate some of the soldering iron heat, especially if you aren't using a station, so a little extra time on those joints will help.

-PB

[Natural Sound]

Thanks for the clarification. I do have a soldering station (HAKKO 936). The connections look solid but I'll re-flow them anyway.

In order to "flip the boards over" I had to remove them. Here are the pictures.

[Grainger49]

On the top board, along the top edge I see two almost spherical solder joints.  I think that the solder pad didn't get much heat. 

Look at the solder joints on the vertically oriented transistors.  Some look just right but a few are again spherical.  It doesn't join the circuit trace and the component lead well.

I'd reheat the ones that look too round.

[Natural Sound]

On the top board, along the top edge I see two almost spherical solder joints.  I think that the solder pad didn't get much heat. 

Look at the solder joints on the vertically oriented transistors.  Some look just right but a few are again spherical.  It doesn't join the circuit trace and the component lead well.

I'd reheat the ones that look too round.

Thanks Grainger. I had a feeling that was going to come up. The photo is deceptive. If I were to turn the board on edge you'd see that the solder joint is more like an inverted V than it is spherical. If anything they have too much solder. The "vertical transistors" are actually the LED's.  And again are not accurately represented in the photo. That said I'll hit those again with a little heat.

This shouldn't be that hard. Four resistors have been replaced with four constant current circuits. I'm pretty certain that I got some bad parts. It happens, I've seen lots of examples of this in my 35 years in the electronics industry.

At this point I have two options. I can eat the $350 for the upgrade kit and put the FPIII back to stock. Or I can buy new components, rebuild the boards and start over at a later date.

Neither of these options are desirable but I'm out of options.

[Doc B.]

It's quite possible that the transistors are shot, but at a certain point it gets a little difficult to work out what has gone wrong by long distance. You can check the transistors for shorts between the leads, but be forewarned that a bad one doesn't always show up with that test. You can also send the preamp to us and we can make it work for you.

[Natural Sound]

OK Guys, don't give up on me yet.

I went with a troubleshooting method that I recommended earlier. I removed the C4S boards and tacked the 22.1k 3/4 watt resistors to the wires that were attached to the C4S boards. The idea being that if this worked I could rule out any wiring mistakes. I re-connected the Shunt Regulator board that had been bypassed. Fired it up and the 4 LED's on the SR board as well as the cathode LED on the tube sockets illuminated "normally." Measured the "O" voltages for the left and right supplies and both measured 149v. Good.

What I know.
1. The two HV power supplies and both sides of the shunt regulator board are functioning.
2. The C4s boards are not working but the wiring to them is good.

This prompted yet another inspection of the 2 C4S boards.
LED's installed correctly - Check
2N2907A transistor orientation and location Q1 on side A - Check
2N2222A transistor orientation and location Q1 on side B - Check
Measured 2ea 75k ohm resistors in position R2 - Check
Measured 2ea 237 ohm resistors in position R1 - Check
MJE350 transistor orientation and location Q2 on side A - Check
MJE340 transistor orientation and location Q2 on side B - Check
Black wire jumper connecting G to G - Check

Rechecked solder connections.

Measured for shorts across transistors - Check
Measured for shorts across LED's - Check

I'm very confident that I did everything as instructed. Whatever the problem is it exists on both boards which seems a little strange. It has to be component related, right? Am I missing anything?

[Paul Birkeland]

I'd be nearly certain at this point that your LED's are not oriented properly. 

-PB

[Natural Sound]

I'd be nearly certain at this point that your LED's are not oriented properly. 

-PB

I'll see if I can get them out without destroying them..

.

[Natural Sound]

Removing the LED's was easier than I thought. The leads are close enough to heat both pads at the same time. On the other side of the board I grabbed the plastic body of the LED with needle nose pliers and applied gentle pressure outward. Piece of cake.

While removing the LED's I paid close attention to the orientation. I was hoping to find a smoking gun but they were installed the way I remember when I built the boards. Darn.

So I went back to the instructions and read the section regarding the LED installation. Then I saw it. The B side LED's were supposed to be in reverse orientation from the A side on the C4S boards. I missed that part and installed them in the same direction (cathode (silver stripe) all in the square shaped solder pad) like on the SR board. BTW the instructions were crystal clear about this. It was just a bone head mistake on my part. I usually don't miss details like that. I make no excuses, it just happened. {smacks self in head}

Powered up and all the LED's illuminated. Moved on to checking voltages and everything was in spec.  Installed into my main system rack and she is providing beautiful music to my Paramour II's.

In retrospect the dark LED's on the B side of the C4S boards should have been a dead giveaway. Oh well, live and learn.

Big thanks to all that helped especially PB! This was a humbling experience and I'm eating a big piece of humble pie.