It Can Happen To Anyone, Trouble After Speedball Upgrade

[Grainger49]

I got a Crack sent to me.  Its initial problem was easy.  I got it working and it sounded quite fine on my old 1980s headsets.

So I built the Speedball upgrade, reheating all solder joints several times before installation.  When installed I used my meter to verify that the wiring to the Crack was continuous, I rang it out from the lower terminal to a component that is attached to where the wires entered the boards.  All was good here.

These readings were taken on two different start ups.  The first ones, the boards were taken 5 minutes before the tube pins.  The amp was off in between.

Here are the input and output voltages for the C⁴S boards:

Large board (all 4 HLMP-6000s light)

Input 1: 179V
Output 1: 172V

Input 2: 179V
Output 2: 61V  (Working??)

Left small C⁴S board (right channel, both HLMP-6000s light):
Input: 179V
Output: 176V

Right small C⁴S board (left channel, first HLMP-6000 lights):
Input: 176V
Output: 0.8V

12AU7 pins:

A1: 0.4V
A3: 0.8V
A6: 174V
A8: 1.6 LED night lighted

6080 pins:

B2: 178V
B3: 171V
B5: 178V
B6: 60.3V

I have tried sussing it out looking at the schematic.  The right (left channel) C⁴S board intermittently has one or both LEDs out.

Help please!

[Paul Birkeland]

Try putting the 22k resistors back to see if the circuit will function.

[Grainger49]

I'll try this when home from work today.

[Grainger49]

Paul, sorry,

So... it took two days.  I used jumpers to put the cathode resistors back in since the leads are minimal on one resistor.  It is just a test!

Put the resistors in, both cathode LEDs lighted.

The first cathode is 1.59V the second cathode's HLMP 6000 went out when I touched it.  I reheated this LED, to no avail.

I bought a bag of HLMP 6000 LEDs a year or more back.  Just for this kind of situation.  They are physically smaller but have the same forward voltage as the Bottlehead supplied HLMP 6000s.  I used jumpers to put one in between the cathode pin and the ground.  Both LEDs lighted! ! !

The plate on one side is 96V and on the other side is 87V.  Does this sound good?

So what is next?  Maybe transistor pin voltages or just put the boards back in withe the new HLMP 6000?

[Paul Birkeland]

How are the voltages at seven and nine?

If they are up around 100V, then it's just down to debugging the large PC board.

[Grainger49]

Terminal 7 is 58V and Terminal 9 is 62V.

How are we doing?

[Paul Birkeland]

No, this is not good.

You have 12AU7 plates at 96V and 87V. 

You have 6080 grids that are therefore at 96V and 87V.

Your 6080 cathodes are at 58V and 62V. 

The grids are positive with respect to cathode, which is no good.  Are you 100000% sure that the R1's are in the correct positions? 

[Grainger49]

I am 100000% certain.  I'm old and slightly dyslexic so I measure everything with my Fluke before installation.

On the large board R1, in circuit measurements: 31.8 and 31.8 Ohms

Left channel R1: 236.1 Ohms

Right channel R1:  238.6 Ohms

When my wife gets home I will do a full voltage check and post the irregulars.

[Grainger49]

Well, crap!  She got home and now the HLMP 6000 I had clipped in isn't lighting.  It was when I posted the last voltages.

Now I have to get that right and I will give a full set of irregular voltages.

There will be more delay in that.  We have company coming tonight and I have to clean things up.  Like I need to get the printed Crack/Speedball manual and the extraneous sheets off of the den's coffee table... that kind of stuff.

[Grainger49]

Ok, I'm home today and troubleshooting.

Here is where I am.  The 12AU7 C⁴S boards are replaced by the resistors.  I replaced the A8 to ground HLMP 6000 LED, it broke while troubleshooting.  All 6 HLMP 6000 LEDs light now.

Incoming voltage 124V AC.

Voltages out of spec:

T1: 91.4V should be 75V
T7: 116V should be 100V (Close)
T9: 115.3 should be 100V (Close)
A6: 90.7V should be 75V (Close)
B1: 90.6V should be 75V
B3: 116.9V should be 100V
B4: 87.2V should be 75V (Close)
B6: 116.3V should be 100V

I realize the A voltages might be off because of the lack of the C⁴S boards.

[Paul Birkeland]

T1/T5 are the plates of the 12AU7.  The "strength" of the 12AU7 will determine just how much voltage is dropped across each 22K resistor, and 75-90V is pretty normal to see here.

[Grainger49]

So, you are saying that the circuit is working properly and I can put the small boards back in?

[Grainger49]

Well, I did that.  The B (Left) channel C4S LEDs (all 3) didn't light and the right LEDs (all 3) did light. 

The right channel C⁴S board's output is 174V, input is 178V (what is wrong here?).  The left C⁴S board input is 178V output is zero.

I reheated the transistor leads on the left channel board, verified the orientation of the transistors and measured the resistors on the boards.  Nothing gained here.  Resistors are right values and the transistors are right (orientation and numbers).

Should I start measuring the voltages on the transistor legs?

[Paul Birkeland]

I would purchase replacement boards or repopulate all the transistors. 

[Grainger49]

Paul,


I can get the transistors out and replaced pretty easily.  I'll contact Eileen. 

This is not my Crack, I'm doing it as a favor for someone else.

Edit: I called, Eileen is always a pleasure to talk to and deal with.  She sent them out the day of this post.