[resolved] Crack + SB Woes. Left Channel dies after 5 minutes

[adydula]

I looked at my working Speedball in my crack and here is what mine looks like:

Its very different looking to mine??

Wondering if this is a later or newer version??

Alex

[Paul Birkeland]

We did do a minor revision to design out those jumpers and replace the front PC board.

Is the hardware nice and tight between your TIP50 transistors and the heatsinks? 

[Blue]

Yea the TIP50 is screwed nice and tight against the heatsink. Any tighter, I think I would start stripping the screw and or the nut.

[fromnowon]

By the way, I can't help noticing that the soldering on your boards looks beautiful!

I wonder what kind of solder you used . . .

I'm sure that you will get this sorted out!

[Blue]

Thanks for the compliment, but my soldering skills are still quiet amateur haha.
I use a standard 60/40 rosin core solder.
I bought this one on ebay: https://www.ebay.de/itm/321315268878

I work as a software engineer at an automotive firm, and we have a hardware department, so I have good access to a ERSA RDS80 soldering station with all sorts of iron tips. It makes soldering easy from tiny SMDs to point to point. My boss encourages everyone to use the work stuff after hours for their own personal projects.

[Blue]

So far it has been 10 days using the stock crack with the small board. No problems so far.
I'd like to attempt to reinstall the big board in the crack.

I haven't done any soldering rework on the big board yet. Any suggestions on what I should do before I put it back in?
I'm tempted to resolder all the components for the left channel on the big board, however I am waiting on a new set of LEDs before I do that (I read that one shouldn't reflow the LEDs due a high possibility of them cracking on a reflow).
How tight does the transistor need to be against the heat-sink? I can't tighten it anymore that I originally had it.
However, for the right channel, all i used was a flimsy screw driver and a pair of pliers, and yet the right channel has non of the problems I have in this thread.

Could this problem occur from any other places? Perhaps poor solder join somewhere else?

[Paul Birkeland]

It might not be a bad idea to replace the TIP50 and 2N2222 where you originally had the mounting insulation issue (A side).

[Blue]

I did replace both the TIP50 and 2N2222 once already. When I replaced the two, the crack worked without problem for two weeks.
Once the problem occurred again, it would fail after 5 minutes of operation like originally. I have another 2N2222 and a few TIP50s remaining.
Once the LEDs come in, I'll replace all of them at once.

[Paul Birkeland]

It would also help to know what voltages change once the board stops working.

[Blue]

So I decided to try just replacing the 2N resistor and TIP50 in the meantime.
Before I removed the 3kohm ceramic resistors, I did a full resistance and voltage check, all good.

Now I attempted to put back the big board. This time the B+ voltage on the bigboard fails. It falls to 112 volts. I only quickly checked OA/OB (they were about 79 volts), but stopped measuring because I started to feel an intense amount of heat coming from the Crack. I didn't want to destroy any other components  Did I destroy my big board? I wouldn't be surprised as I have reworked it many times now.

Therefore I put back the 3kohm resistors and left the small board in. I did a full resistance and voltage check, and everything seems to fit, other than T2 and T4 being a bit higher than the tolerances., but I am guessing that is due to the small board

Here are my voltage checks with stock crack and small board:

T1: 80.8
T2: 197
T3: 0
T4: 197.2
T5: 83.9

T6: 0
T7: 111.1
T8: 0
T9: 117
T10: 0V

Small board:

OA: 80.5
IA: 196.6
B-A/B: 0
IB: 197
OB: 83.8

Should I just give up on the big board and order a new one? I'm afraid that eventually I'll destroy my transformer.

[Paul Birkeland]

If the B+ voltage drops like that, the TIP50 transistors are not properly insulated from the heatsinks.

[Blue]

I’ll get back to it again on the weekend.
As for mounting the tip 50, it goes screw, Fiber washer on top with protruding end facing towards the insertion side, transistor, thermal insulator tab, heat sink, metal washer, lock washer, nut.

I’m sure my picture shows that too. I find it perplexing that isolating the transistor is so complicated .
I’ll take a picture of each step of mounting the transistor against the heat sink.
I’m also tempted to try one of your tests in an older thread: pulling back the transistor from the mounting kit, and measuring the voltages then, running the amp for no longer than 30 seconds

[diynewbie]

I  would think that you could check continuity or resistance between the heat sink and metal tap on the transistor to verify proper installation. Correct?

If the shoulder on the fiber washer did not seat properly it could result in a short between the transistor and heat sink even if order and orientation of all parts are correct.

[Tom-s]

This might help.

It's essential that the screw with fiber washer are centered in the transistor.

[Blue]

Yea I followed the exact same video when I originally built the speedball, and probably watched it another 10 times trying to solve this problem.

I also checked for contact between the transistor metal tab and the heat sink.
My Multimeter was not beeping. The transistor is currently disassembled from the heat sink. I’ll be trying it again on the weekend.