Speedball upgrade fail - please help

[vincentquy]

I have been using my stock built crack for a week and today I attempt to upgrade the speedball.
I follow the instruction and make sure I soldered the right joint and in correct orientation.
I proceed to check voltage of the small board.

OA: 68V
IA: ... the produces a spark at the ground bush (12U)

Now all measurement give something like -0.1V. The tubes still glow when I plug in power. But there is no sound coming out. I tried to revert to pre-speedball built but now the LED won't glow.

PLEASE HELP!

 

[Paul Birkeland]

Can you check to see if the fuse is still in tact?

68V at OA would've been an OK voltage. 

You are saying when you touched the probe to IA, that there was a spark at 12U?  Were you using a clip lead or perhaps did your hand slip with the probe back by 12U?

For future voltage checks, you can wedge the black probe against the bare wire between the two RCA jacks if you don't have a clip lead available.

 

[vincentquy]

The fuse is intact.

Yes, that's what happened. I don't have a clip but I didn't slip the probe. I keep the black probe at 12U and use the red lead to touch IA and there was a spark.

Now, the 2 LEDs at 9 pin socket won't light up anymore. All the measurement give me -0.1 V and doesn't give any resistance.

 

[Paul Birkeland]

If the fuse is OK, move along to the checks in the manual for wall voltage and power transformer voltage.  Your power transformer is just fine, but it's important to double check that the amp is at least able to make the DC voltage you appear to be missing.

Also double check that the 12AU7 and 6080 are glowing when you turn the amp on. 

 

[vincentquy]

I just got these measurement (the crack is in stock form)
Both tube are glowing
---Voltage Check 1:
NL: 121.7 V
Transformer 7 – 9: 5.8
Transformer 11 – 12: 176.8

---Resistance Check:
Terminal 3: 0 ohm
6: 0
7: 2.84
8. 0
9. 2.67
10. 0
12. can’t measure
14. can’t measure
20. can’t measure
22. 0
B3: 2.47
B6: 2.46
RCA center pin: 103.5

---Voltage Check 2:
Terminal 1: -1.4 V
2: -1.4
3: 0
4: -1.4
5: -1.4
6: 0
7: 0
8: 0
9: 0
10: 0

 

[Paul Birkeland]

Can you carefully measure the DC voltage between 20 and 21? 

You have AC voltage coming out of the transformer, so the lack of DC voltage is unlikely.  The more likely scenario is that there's a bad solder joint that's no longer passing this along downstream.

 

[vincentquy]

By "measure the DC voltage between 20 and 21" do you mean the black lead at ground and the red lead goes to 20 and 21?

 

[Paul Birkeland]

No, one probe at 20 and the other probe at 21.

 

[vincentquy]

After a day of fixing, I managed to make the crack work with the small board. You were right when you said there's a bad solder joint somewhere. I reheat/ resoldered most of the joint and it's now working. I will take a rest before upgrading the larger board. Blowed a fuse tho.

 

[Paul Birkeland]

Yeah, bad solder joints can creep up at the strangest times.  I've worked on Dynaco ST-70s built ages ago that had solder joints that were completely missed but started acting up after a round of shipping. 

 

[vincentquy]

Is it normal to have channel imbalance? My left channel is louder than right channel I have to adjust on my PC to have balance.

 

[Paul Birkeland]

See #3/#4.
Crack FAQ

 

[vincentquy]

Will that work if I use the Alps Blue Velvet pot? Also, where can I buy those resistors?

 

[Paul Birkeland]

Yes, that will work with the Alps pot.  Does the place where you bought the pot sell resistors?

 

[vincentquy]

Are these compatible?
https://www.partsconnexion.com/TAKMAN-80372.html
https://www.partsconnexion.com/TAKMAN-73048.html

 

[Paul Birkeland]

Those are 75K and 33K resistors, yes. 

 

[vincentquy]

I just finish the large board speedball upgrade. Sounds really awesome.
However, the measurement is as follow:
OA 90V
OB 105V
G 0 V
B+ 180V

OB is a lot higher than OA, is that normal?

Also: are these capacitor similar to those come with the stock Crack?
https://www.partsconnexion.com/NICHICON-76189.html

 

[Deke609]

are these capacitor similar to those come with the stock Crack?

Those are snap-in capacitors for pcb boards. The very short leads will make installing them very difficult. But electrically they should work like any other good 220uF 250VDC cap.

PB may want to chime in here to confirm, but generally BH specs capacitors (and other parts) with long operational life. The following link will take you to a search page on Mouser showing in stock options for Nichicon radially leaded (what you want) 220Uf 250VDC caps: http://www.mouser.com/Nichicon/Passive-Components/Capacitors/Aluminum-Electrolytic-Capacitors/Aluminum-Electrolytic-Capacitors-Radial-Leaded/_/N-75hqwZ1yzvvqx?P=1z0zlbmZ1z0wrjqZ1yzs9nv 

If you scroll to the right you'll see the "Life" column showing how long the various caps are expected to perform within spec at their max rating. The figures range from 1K to 10K hours - i.e., some caps will last 10 times longer than others.

cheers, Derek

 

[Paul Birkeland]

OA 90V
OB 105V
OB is a lot higher than OA, is that normal?

You'll probably find that OA and OB on the small board are a little different, and that difference is carried over to the 6080 and reflected in the operation of the big PC board.  Some variation here doesn't make much of a difference.

Also: are these capacitor similar to those come with the stock Crack?
https://www.partsconnexion.com/NICHICON-76189.html

We would try not to use a part with such a low life rating.  I would consider those a downgrade from what we usually provide. As Derek also mentioned, mounting snap-in capacitors on terminal strips isn't always the easiest thing to do either.

 

[vincentquy]

@Deke609: Thank you for the information!

@Paul: I see. Do you think the Voltage difference is the reason why my left channel is louder than right channel? I used APO to correct the imbalance and find that left channel is about 3dB louder than right channel.