Help with Speedball upgrade

[aztlan667]

Hey guys.  I just finished putting together the Speedball upgrade for my Crack.  I had a working Crack amp before the upgrade but I believe there was an issue with the initial wiring.  During testing after the upgrade, when I would push on the black wire leading from the left input jack to the lower lug of the potentiometer the sound would pop and cut out and the LEDs would blink off.

I've tried reflowing the solder joint at the potentiometer but it hasn't made a difference.  In fact, I seem to be making things worse, since now the LEDs won't come on at all. Also, since the solder joint is in a difficult to reach spot surrounded by wires I keep burning insulation on the surrounding wires trying to reflow the joint.

My initial Crack build passed all resistance and voltage checks as did the Speedball upgrade.  But now everything is screwed up and I don't know how to test the original resistances since I've removed the 4 resistors as part of the Crack upgrade.  Can someone clue me in on what the resistances should be after the Speedball upgrade?  Anything else I should be looking at?  I can post my resistances/voltages if you want.  Thanks!

[Paul Birkeland]

Can you post pictures of what you have? 

A few black wires meet at the headphone jack, one of those wires is loose on one end (not necessarily the potentiometer end, maybe the other end of any of the wires that land there).

[Doc B.]

Could also be that the black wire is broken inside the insulation, possibly nicked by the wire stripper and then cracked when bent.

[aztlan667]

I've attached some picks of my build, which I know looks like it was put together by a chimpanzee with epilepsy.  But since this was my first ever DIY project, I'm amazed I got anything to work at all.  I've included shots of the potentiometer joint, the 9-pin socket, and the ground tab, which right now is showing infinite resistance.  As you can see, I've made a hash out of the wires around the potentiometer joint trying to reflow the solder.

Another interesting thing I've noticed; when I was doing some voltage measurements, I inadvertently touched the base plate with my probe while also touching the potentiometer lug.  This caused all the LEDs to light up so I'm guessing it shorted the circuit to them which was previously open.

[Doc B.]

You need to reflow all of your solder joints. Make sure that the tip of the iron is touching both the wire and the terminal, and make sure the solder flows onto both and makes a fillet at the joint. The safety ground tab is particularly bad, but there are several others that need a reflow as well. Just do them all and you will probably be in good shape.

[aztlan667]

Will do, Doc. Can you tell me if the resistances I’m testing are the same as the vanilla Crack? I’m assuming some resistances should be different.

[Paul Birkeland]

Any resistances in the original manual that should be 0 ohms will stay zero ohms.

The rest of the resistances will depend greatly on the meter and aren't very helpful for debugging.

[aztlan667]

So I've reflowed all of the joints that looked suspect and I've replaced the wire grounding the input jacks, which must've been nicked as Doc said, since it was showing intermittent resistance.  This appears to have sorted out my grounding issues.  Thanks for the help Doc and CB!

However, now I'm getting low voltages across most of the Speedball's input terminals.  Here are the voltages I'm getting.

Small Board

OA        48V
IA         89V
B-A/B   6.2mV
IB         96V
OB        85V

Large Board

OA        84V
OB        48V
G          6.9mV
B+        94V

So with the exception of OB on the small board and OA on the large board, all voltages are around 40% less than what they should be.  3 out of 4 LEDs are lit on the small board and 2 out of 4 on the large board are lit.  Also, when I power the amp I notice a funny smell coming from around the power transformer.  There is no smoke, but the 270ohm resister connecting 21U and 15U gets EXTREMELY hot. 

I'm assuming there's a short somewhere draining current but I've looked at every joint and they all look good.  I'm not seeing anything touching another joint or anything touching the chassis.

Can you tell me if there is somewhere specifically I should be looking?  i.e., the transformer connections?  Or could it be the connections on the speedball boards themselves?   Thanks again for the help!

[Paul Birkeland]

Check the wiring from OA and OB on the big boards to be sure they go to the correct terminals.

Did you do the intermittent test of running the amp with the small board + 12AU7 but not the big board?

If you run the amp with the 12AU7 and no 6080, how are the voltages on the small PC board?

[aztlan667]

I ran the amp with no 6080 and the voltages on the small board look correct.  However, the LED closest to 1A still doesn't light up. 

I've attached pics of my large board.  I don't see anything wrong with the joints but maybe I'm just not looking for the right thing.

[Tom-s]

If i look at your board i'd reflow both center lugs of the TIP-50 transistors (both).

[Doc B.]

You have two LEDs with bad solder joints. Just reflow everything on the board.

[aztlan667]

I've reflowed every joint on both boards, paying extra close attention to the center lugs of the TIP-50 transistors. I've made sure all joints are properly hot enough so that the solder flows well and cools to a shiny finish.

Unfortunately, I'm still getting exactly the same voltages on the large board.  Is there anything else you can think of that I should look at?  Thanks again.

[Paul Birkeland]

Can I see a shot of the octal socket area? 

What you're experiencing with the big board seems a lot like the TIP50 transistors aren't installed properly, but you have voltages at OA and OB that aren't the 0V that I would expect from this issue.

The other problematic situation is when the B+ wire for the big board isn't connected to the correct terminal.

[aztlan667]

Here are a couple pics.  I've re-flowed all of the octal and 9-pin connections as well, with no effect.

I'm fairly certain that the TIP-50 transistors are installed correctly.  They're oriented just like it looks in the manual.  Also, the B+ wire is terminated to 4U, per the manual.