[Speedball] Big board voltage (RESOLVED)

[Manuel Parent]

Hi,

I'm almost done assembling the speedball upgrade. Voltage on the small board were all good. Resistance on the big board were reading around 25MΩ or OL. I guess it's good since it's supposed to be very high.
Voltages on the big board are wrong however. G and B+ are good, but OA and OB read respectively 123V and 107V. All led are lit.

Any idea what could be wrong here ? I attached photos of my boards.

Thank you !

 

[Paul Birkeland]

What are OA and OB on your small board looking like?

Reheating the joints on the big C4S board never hurts when it isn't working properly.

-PB

 

[Manuel Parent]

Around 75V each (73V for OA, 76 for OB).
By C4S board, you mean the big one ? If so, I'll redo a quick pass on the joints tomorrow, to make sure everything is soldered properly.

 

[Manuel Parent]

I've done a pass on joints on the big board. Still no luck  :-\

 

[Paul Birkeland]

Could you post some updated photos of the build?

The 107V isn't a problem, but the 123V is a bit out of range.

 

[Manuel Parent]

Sure, here you go ! Let me know if there's something in particular you'd like to see.
I should probably mention that I messed up with one 2N2222A transistor (the one near OA) and had to desolder it and reorder one on digikey. I got this one : https://www.digikey.com/product-detail/en/central-semiconductor-corp/2N2222A/2N2222ACS-ND/4806845
The desoldering part was not easy to me, and it's entirely possible that I did something wrong here.

Edit : added a photo of the underside. I can't do any better without either desoldering the wires or cutting them, Let me know if you need it !

 

[Paul Birkeland]

These are still not soldered all the way.  You may need to hold the iron on these joints much, much longer, but one of them does look good.

 

[Paul Birkeland]

Here's another one.

-PB

 

[Manuel Parent]

Hello,

So I resoldered the joints you mentioned and I rechecked the other joints. Still no luck, I still get around 124V from OA and 104V from OB. I attached some updated photos.

Quick safety question while I'm at it. When resoldering the wires of the big board, I accidentally soldered the board backward... Of course, nothing worked, so I promptly unplugged the amplifier, waited for 1-2 minutes and tried desoldering the cables, and I took an electric shock, which left me a bit... shocked. (pun intended) The blue capacitors were still charged around 40-50V, going down really (really) slowly. I discharged them and resoldered the board the right way. Now it's back to how things were before (tube lit, LED lit, same voltage readings as before), so I assume I didn't fry the power supply at least. Can I safely assume that my mistake will have no further consequences ?

Thank you !

 

[Paul Birkeland]

The 100uF caps discharge through the 2.49K resistors on the headphone jack, or through the solid ground connection on the headphone jack itself.  If these are not discharging, then there's an issue with the build that was present before you installed the Speedball.

There are still some solder joints where the solder isn't wicking all the way up through the hole.  It also looks like the wire going to B6 isn't soldered well at B6.

 

[Manuel Parent]

Strange. Is it possible that the amplifier was working despite this problem ? The amplifier passed all tests and it did work fine. I even used it for a whole week before I started working on the speedball.

Anyway, before anything else, I'll try fixing that issue with the capacitor not discharging, as it's making working on the amplifier downright dangerous. I'd rather not have it discharge to my heart.
Upon rechecking with the now properly setup board, only the capacitor on terminals 9-10 is not discharging. When I check for voltage, it's dangerously high (around 120V). Based on what you said, it's probably a bad solder on the way to the headphone jack/headphone jack ground, right ?

When I'm done with that, I'll redo those other solders.

 

[Paul Birkeland]

Follow the wire leaving OA to the terminal strip, then to the tube socket.  I would bet the wire between the terminal strip and the tube socket isn't well soldered. 

 

[Manuel Parent]

I resoldered the capacitor. It was hard to bend the legs because they were inserted from the other side. Now it's much easier to bend them out of the way for the big PCB. I also went and added some solder to the joints on the way to the tube socket, to the headphone jack and the ground near the power socket. It's no use, the transistor is still fully charged when unplugging the amplifier. I attached some new photos I made after resoldering all that.

 

[Paul Birkeland]

That's still looking cold.  You want to see the solder flow around the wire.  If it doesn't, the flux will float to the top of the solder and insulate the solder from the wire if the solder doesn't flow all the way around it.  More heat is the answer here.

 

[Manuel Parent]

Hello again !

I resoldered the joint you mentioned. Should look much better now. I attached a photo.

That said, the capacitor is still charged when unplugging the amplifier. I figured I'd do some additional tests before coming back to you :

• Black lead on 10, Red lead on B6 : 120V
• Black lead on 10, Red lead on OA : 120V
• Black lead on headphone jack, Red lead on 9 : 120V

Does that mean that electricity can travel between this points ? If so that would exclude a solder issue on those specific points.

 

[Paul Birkeland]

I'm still nearly certain that this is an issue of flaky solder joints, perhaps made worse by lead free solder?

The flat rate repair service may be the most sensible option, or you can put the 3K resistors back in and replace the transistors on the PC board on the offending side.

 

[Manuel Parent]

The solder I use is rosin core, Sn60/Pb40, so it's definitely not lead free. The repair service does seem like an option, but I'd rather do everything I possibly can before I go for it. Having someone repair it for me kind of kills the DYI appeal. If by the end of the week I don't find what's wrong, I'll probably go for that.

Just to be sure I fully understand, what does this capacitor do and where should it discharge ? (and actually, how does a capacitor discharge ? none of the other seem to be having any kind of issue) Also, what transistors are you talking about ?

 

[Paul Birkeland]

On the big PC board and the half that isn't working, there's a TIP50 and a 2N2222.  I would remove and replace those two parts.

 

[Manuel Parent]

YAY, I'm finally getting the right voltage and the amplifier works !

Ok, just to summarize what happened. Back when I first assembled the big board, I accidentally soldered several terminals of the 2N2222 together. I tried to remove the excess with a desoldering bulb and failed miserably. I insisted when I shouldn't have and probably ended up burning the hole without realizing it. Later, I bought desoldering wick and it went much, MUCH better.
Anyway, you told me to check the transistor and so I did. Resistance was reading OL between the holes of the transistor and the next point on the PCB... So I did what I had to do and bypassed the PCB with wires. (see attached photo)

I have to say I'm not 100% confident about my approach (not that bypassing sections of PCB is unheard of), but at least it seems to be working fine now.

 

[Paul Birkeland]

I've had to do that once in a while, though never with all 3 leads.  If your DC voltages are where they are supposed to be, I wouldn't worry about it.