Speedball Problems including smoke.

[Pflugshaupt]

Two weeks ago I successfully completed my crack build and it worked and sounded great. Now I tried doing the speedball upgrade, but I have run into big problems I need some help with.

When I completed the speedball initially, the checks were all okay. Some voltages were a bit high, but nothing crazy. I started using the crack with the speedball and initially everything seemed to work great until after some minutes I started hearing noise in the left channel. It was some kind of fade-in / fade-out browning noise that got worse and worse and I also heard some pops and then the big nightmare - white smoke started to come out of the vents. It had the typical burnt transistor smell. I checked everything many times and couldn't find an issue. I removed and reattached the larger speedball board in the process and so I though let's give it another go. I turned it on again flipped around and within seconds I saw smoke coming from the TIP50 closer to the smaller board. I turned everything off, search through the forums in search of an answer. I saw similar problems, but no smoke ever. I'm totally certain nothing is touching anything and that smoke definitely comes from the TIP50 and not from any resistor. Finally I thought maybe I just received a bad TIP50. So I ordered four replacements. I built the crack back to "partial speedball" with just the smaller board and I can confirm it is working just fine in that configuration.

Today I received the replacement TIP50s and I also exchanged the smaller transistor just for good measure. I made absolutely sure the TIP50 middle leg is soldered correctly and that there is no contact between the heatsink and the middle leg. I reflowed all points on the board as well.

When I wanted to measure the voltages with the new parts, I even got flames and smoke again. One of the legs of the new TIP50 started to glow and there was that smoke again. The only other thing I saw in the brief time it was on is that initially all eight speedball diodes lit up, but then the two on the section that is troublesome started to get more and more bright while the others become more faint. Then I turned everything off and now I have no idea what to do. I have 3 more tip50 I can burn, but obviously the problem seems to lie somewhere else and I need some help sorting this out - so please help and thanks in advance! I will now build it back to partial speedball just to be sure nothing else is broken.

[Pflugshaupt]

Looking at the board again it seems there is now a burn mark between the "lower" two legs of the TIP50 in question. Is it possible something is weird with my board?

[Paul Birkeland]

Are you 100% positive that your voltage checks passed when you installed the big board the first time?  It would be  very rare to get the correct voltages, then to blow out a transistor.

Can you post photos of your build? 

[Pflugshaupt]

On the big board the resistance checks on OB and OA showed over-limit.. maybe that was a bit weird because my meter can display mega-ohms. I do not dare try another voltage tests, but I remember G was 0V and B+ was also good. OA and OB were about 110V. Everything seemed to work beautifully initially for at least 5 minutes and I was already trying to listen to the differences when the troubles started. The only thing I can see that I don't feel very confident is how one of the leds on the large board were soldered, but I checked it with the meter and it appears to be fine.

I put some images on dropbox. Unfortunately the one where I wanted to take a photo of the glowing leg is not sharp . I did an emergency shutdown to prevent more damage before I could check.

Should I picture a specific area? Note that my crack works perfectly well with just the small board + the ceramic resistors.

https://www.dropbox.com/sh/v1dabyei4cq7yq4/AACSl2aKISM9dpu1iTHpVWASa?dl=0

There is a movie showing a second test without smoke where the two leds on the bottom glow very bright while the six others are dim. Initially they all light up the same. There's also the very unsharp image of the "glowing" I described, you can see the glowing spot above the leds between the TIP50 legs.

I'm not 100% my replacement tip50 is a correct replacement. It fits perfectly and is specced to 400V. Do I assume correctly all TIP50 models use the same pinout?

I read about 10 threads on this forum about similar problems, but I think I have a different one . I'm happy to picture or measure anything you want.

[Pflugshaupt]

Ok. wow I think I managed to fix the problem myself. I made a direct connection between another TIP50 and the 2N2222A like so:

https://www.dropbox.com/s/lmlao91r3ucu2n3/20171206_212038.jpg?dl=0

No more smoke, no more crazy bright LEDs. Now I could check the voltages and I get these:

large board:

G 0 V
B+ 194.1 V
0B 111.8 V
0A 112.2 V

small board:
0A 71.2 V
1A 193.4 V
A/B 0 V
1B 193.2
0B 70.0

These all seem a bit high but reasonable. As I wrote in another post my mains is 234V so I'm above the 230V baseline and I guess that's why everything is a bit high.

I will now listen to music for some hours (hopefully) and then maybe post again if something has started to burn, but my best guess is that the problem was the PCB itself. Somehow it became a low wattage resistor between those two pins of the TIP50 and almost started to burn from the current.

Maybe the PCB came like this, or maybe I overdid things a bit when I soldered the middle leg with extra temp and made some kind of micro pseudo connection.. is that even possible? I used a good soldering iron set to 360°C (680° F), but for the middle pin I stayed on there for a few seconds just to be sure. Before I made the direct connection I checked the resistence between the two pins and it does read 0 Ohm, so I'm really not sure what's going on.

The bypass I made looks a bit scary, but now if something breaks, at least I'll know immediately where to look!

[Pflugshaupt]

After using the Crack + Speedball nonstop until now I can say it is now working as it should and the problem was caused by the PCB or my solder work at that spot. I'm happy the amp is working and it sounds awesome, but the issue was quite puzzling. I'm also not yet sure I like the Crack more with the Speedball. I am using a Sennheiser HD800 and with the Speedball I do hear additional clarity and more bass definition but I also hear a bit overly aggressive highs which were nicely softened by the non-speedballed Crack.

Is it possible to just order an extra large pcb for the Speedball so I could fix things properly? Or is there maybe a fix I could do to the pcb? A crazy idea would be to just dremel a slot through at the spot - that would ensure it cannot conduct ever.

[Doc B.]

Most likely it was a solder bridge that was hard to spot, or it could have simply been a flux bridge, which can usually be cleaned off with alcohol and a small brush.