[Resolved] Speedball Upgrade Voltage Check Issues

[awkatche]

Just finished installation of the speedball upgrade. My base crack has been running fine for a month or so and has had no issues. Speedball passed resistance checks.

On voltage checks, G was 0V and B+ was at 186V, right within range. OA was at 101V (so just above range) and OB was at 111V, a bit out of range. Wondering what might cause this or if it's simply possible that the voltage ranges can vary a bit beyond what's listed in the guide.

Edit: Ran audio through it and getting only a low 60hz hum in left channel - right channel sounds fine.

 

[Thermioniclife]

It could be that the line voltage is a little high. The voltages listed in the manual were measured at a 120Vac input.
My house consistently runs at 123Vac. Check the outlet with your meter set on ac.

 

[awkatche]

Thanks Lee - last I checked, the line voltage was slightly lower than 120VAC - I think around 118 or so. I'll check again though. That said, I'm convinced I did something wrong as there's no audio in the left channel, just hum - I'll recheck wiring and solder connections in that channel.

 

[Thermioniclife]

Sounds like a plan. Use the working channel to take measurements and compare to the bad channel. I'm sure you will sort it out.

 

[Paul Birkeland]

What are the voltages on your small PCB?

I would recommend posting some build photos and reheating all of the solder joints on your boards aside from the LEDs.

 

[awkatche]

Thanks Doc.

Voltages are

Large Board:
B+ 187V
G  0V
OB 112V
OA 102V

Small Board:
OA 79V
OB 69V
1A 187V
1B 187V
B-AB 0V

Some pictures of my embarrassing soldering skills attached.

Will reflow solder now and see if that helps.

 

[Paul Birkeland]

Just looking at your first photo, I can see down into the holes where the components are installed.  That is indicative that not enough heat has been applied to properly solder these boards.  The solder needs to flow through the board to the other side.

All of the joints on the boards are like this.  You will find that the LEDs and small R1 resistors take the least amount of heat, while the center legs of the MJE350 and TIP50 may need to be heated for 10+ seconds for the solder to flow through to the other side.

 

[awkatche]

Reflowed solder to all points on both the large and small board - I see solder fill the hole on both sides now. Still getting the same voltage readings. Any other areas worth checking specifically? I had to remove some solder and resolder the joints at 7U, 9U, 1U and 5U. Not sure why it would cause these readings though.

Also, worth noting - after installing only the small PCB when I still had the 10W resistors still in, I plugged in audio to test and it worked just fine.

 

[Paul Birkeland]

It's probably work posting some fresh build photos.

 

[awkatche]

Thanks Paul.

Ok, reflowed solder to both the large and small PCBs last night and added a bit of extra solder where it seemed low. I'm now getting:

B+ 181V
G.  0V
OA 106V
OB 106V

So they're equal, but still a bit high. I'm still getting a hum / buzz in the left channel only which doesn't change with the volume. I had no issues prior to installation of the large PCB board. I'm wondering now if the voltages are roughly ok at this range, and maybe the solder connection on 9U to OA might not be great and may need to be reflowed? Would that explain the buzz?

having issues posting photos right now for some reason - hitting 500 error - will try shortly

 

[awkatche]

Top View of Large PCB

 

[awkatche]

Top View of Small PCB

 

[awkatche]

Side view of Large PCB

 

[awkatche]

OB Large PCB Connection

 

[Paul Birkeland]

The TIP50 transistors still look like they could use some solder. 

With some inexpensive headphones plugged into the amp, you can poke around with a wooden chopstick to see if pressing on anything changes the nature of the buzzing, and that could focus your efforts.  The DC voltages you have look OK.

 

[awkatche]

Reflowed solder throughout. Resolved. Not sure what the issue was but fixed at least