speedball - bad voltage check [solved]

[op6980]

Hi,

A month ago I built the Crack and it was wonderful.
Today I have finished installing the Speedball, but have an issue with voltage:

When I turn on the crack I get some high-good voltage reading, but then the voltage get lower and lower and the leds gradually turning off. I see near zero voltage on terminals that should give good readings. Also, at first I saw  some smoke coming from the switch ?! So I turned it off.

Any advice ?

[Paul Birkeland]

Post the voltages you end up with once things have settled.

-PB

[Paul Joppa]

From the limited information provided, I wonder if the power switch is dead, so the amp turns itself off as the power switch slowly fries. It is easily damaged by excess heat while soldering, many here have done that!

[op6980]

From the limited information provided, I wonder if the power switch is dead, so the amp turns itself off as the power switch slowly fries. It is easily damaged by excess heat while soldering, many here have done that!

Crack was working great a day before and I did not touch the switch when I installed the SP, so I do not think it is the switch.

Post the voltages you end up with once things have settled.

-PB

PB, I could not let it settled, as I saw a bit of smoke and smelled some burned plastic, just after 20 seconds.

I touched the 270 Ohm 5W (from 15 to 21) and it was supper hot - Iron level by the touch of it.
From what I do have:
1  0.4V
2  40V
3  0
4  40V
5  40V

Any suggestions ?

[Paul Birkeland]

You have a short in the amplifier.  This happens generally when two component leads touch that shouldn't touch.  You can remove the red wire at terminal 13, then bend it back over the octal socket.

Now, switch the amp on and measure terminals 13/15/21.

If the amp is still cranky and smoking, you have a short in the power supply.

If the power supply is stable (~200V at those 3 terminals), then post back and we can continue diagnosing. 

[op6980]

You have a short in the amplifier.  This happens generally when two component leads touch that shouldn't touch.  You can remove the red wire at terminal 13, then bend it back over the octal socket.

Now, switch the amp on and measure terminals 13/15/21.

If the amp is still cranky and smoking, you have a short in the power supply.

If the power supply is stable (~200V at those 3 terminals), then post back and we can continue diagnosing. 

I have disconnected the red wire from 13 - 13/15/21 yield 230V.
So it's not the power supply...


 

[Paul Birkeland]

OK, this is a good step in the right direction, as we can ignore everything mounted above the power transformer.

The next step is to put that red wire back, then remove the large Speedball PC board.

After this, remove the 6080 tube, but leave the 12AU7 in, then turn the amp on.

We are most interested in seeing the voltages at T1/T5.  Everything else is irrelevant at this stage of diagnosis.

-PB

[op6980]

T1  77V
T2  217V
T3  oV
T4  216V
T5  83V

and all the leds are nicely lit.

[Paul Birkeland]

Well, this is very good! 

This step has told us that you have all the transistors in the correct places (whew!), and all the resistors in the correct places. 

We now also know that the only possible source of issues is on the large Speedball PC board.  It is totally possible to wire this board so that it shorts out the power supply.  If a wire left one of the "B+" pads and hit one of the "G" pads, you'd end up with one angry Crack!

If that's not what's happening, feel free to post pics of your big Speedball board and the current state of the Crack with all the little teflon wires sticking up.

-PB

[op6980]

Wow,
At least I am getting somewhere - Big PC.
But still, cannot pinpoint the problem, to get a solution.

Maybe different eyes...

[Paul Birkeland]

There is another possibility -

If the metal tab of one of the TIP50 transistors is allowed to touch the heatsink, you will essentially create a short, as the 6080 will draw a crap ton of current.

You can test this by measuring the resistance between each "O" pad and one of the solder joints that holds the adjacent heatsink to the board. 

This would also be testable by running the Crack with this board reinstalled and no 6080 tube.

-PB

[op6980]

I have reattached the big PC board and turned on the power (without the 6080 tube).
I could see some reading of several KOhm between one of the 'O' pads and its heatsink joits.
The other showed nothing - zero or near zero resistance.

What is that mean ?
there is no visible connection between the TIP50 and the heatsink (besides the bolt attaching it).

[fullheadofnothing]

The TIP-50 should be isolated from the heat sink with the transistor mounting kit (see p. 15 of the Speedball manual), specifically the shoulder washer and the thermal pad. If you've missed either of those, there's the problem.

[op6980]

Fantastic !

There you go !
Did not put the Fiber (thought these were plastic) shoulders. Silly me !

I installed them - Perfect !

Thank you guys !
You are the best !
I have learned so much in the process.

[Grainger49]

   .  .  .    you'd end up with one angry Crack!   .  .  .   

That is a bad mental image.