My Crack Smokes [solved]

[captain widwiki]

Hello everyone,


I've upgrade the crack with the speedball but when I was about to check the voltage the 270ohm 5w resistor between 21U and 15U started to get very hot and to smoke. I've shut it down immediately and I've check all wiring and solder joint but I did not find anything wrong. So I've decided to return to stock to see if it was only a speedball problem. The stock crack wasn't too hot or smoking and was playing fine but when I've check resistance I've noticed that T6 and T9 are now showing 0. All other values seems fine.

[Paul Birkeland]

when I've check resistance I've noticed that T6 and T9 are now showing 0. All other values seems fine.

Did you perform the modification on the headphone jack mentioned on this forum?

Generally, a Crack will smoke when the Speedball is installed if the TIP50 transistors are improperly mounted.

One way to check for this is to put the Speedball back in and run the Crack with just the 12AU7.

On the bigger Speedball board, the TIP50 transistors must have no metal-to-metal contact with the heatsink. If the hardware is not properly installed between each TIP50 and heatsink, you will create a short once the amp warms up.

-PB

[captain widwiki]

Yes I've performed the modification on the headphone jack. Here some pictures of the TIP50 transistor if it can help

[Paul Birkeland]

Is the washer under those screw heads metal?

[captain widwiki]

yes

[Paul Birkeland]

Please try installing the washers that we provided with the mounting kit.  They are there to prevent just this exact problem, and your metal replacement may have destroyed the larger PC board.

[captain widwiki]

Sorry I misunderstood your question ... I only have used washers from the kit so it may be something else

[Paul Birkeland]

There are plastic insulating washers installed between the screw heads and the TIP50 metal tabs.  If you placed the metal washers that came with the kit in this position, this would also cause your problem.

[captain widwiki]

I've checked the speedball pdf on this step and it says "slip the Fiber washer onto the bold provided". So you mean a made a mistake using another stock washer (metal) instead of  plastic one right ?

So I've to use the white washer from the picture

[Paul Birkeland]

So I've to use the white washer from the picture

Yes, fiber is plastic (not metal), so you need to use the white washer.

[captain widwiki]

Ok thanks I keep you inform

[captain widwiki]

Problem solved ! I've put the fiber washer and my crack don't smokes no more but now when I plug the jack (without source) there is a loud noise in both channel (but louder on the left). This buzzy noise is louder when the volume pot is at 0 and decrease at higher volume (but is still louder than anything i've heard). There is also a scratchy noise when I increase the volume the first time but not each time I touch it.

[Paul Birkeland]

Please measure your voltages.

By not installing those fiber washers, you have put the amplifier under amazingly high stress, and it wouldn't be surprising if there are stressed components that need to be replaced.

[captain widwiki]

T1: 155
T2: 382
T3: 0
T4: 382
T5: 158
T6: 0
T7: 190
T8: 0
T9: 176
T10: 0
T11: 0
T12: 0
T13: 383
T14: 0
T15: 425
T20: 0
T21: 466

[captain widwiki]

Don't know if it affect the voltage but I've used a Tung sol 5998 for the test.