ACA Power issues

[richard t]

HI Folks.
I finally decided to dip my toes into building an ACA mini amp,
I assembled the PC and believe all the components are installed properly. not the best looking solder joints but they seem to be OK, however I can't seem to get it to power up.
I tested the power supply and it does test at the proper voltage. 23.88vdc.
The power light blinks slightly every 4 seconds but doesn't stay on.
Also, when I plug the power supply in, an arc jumps from the outer barrel on the plug to the outer wall of the input jack.

Can anyone point me in the right direction to trouble shoot the issue.

Thanks in advance.
Richard

 

[Mulburg]

Can you post a picture of your back panel wiring and the insides in general?

 

[rayma]

Are you using the spec power supply SLE48S2403N01, and if not, is the center of the plug positive?

 

[richard t]

 

[richard t]

Not quite sure what you meant by wiring but here are a couple images. I removed the input jack to test it and it seems fine.
I am using the supplied power supply.

 

[rayma]

I would go back through the assembly instructions step by step, and check everything.
Male sure each part is in the right place. Look for reversed semis, or wrong resistor value.

 

[KevinHeem]

Before plugging in the power supply, all four potentiometers are turned fully counterclockwise and the amp is switched off?

 

[richard t]

I would go back through the assembly instructions step by step, and check everything.
Male sure each part is in the right place. Look for reversed semis, or wrong resistor value.

I'll do that and let you know.

 

[richard t]

I checked all the locations and everything is in the correct locations. I measured all the resistor values and there are 2 sets that are the wrong values. R2 and R3. All 4 read 105k when they should be 200k and 221k respectively. All the resistors were measured prior to installation and read properly. should I replace them or could something else be screwing with the values?

 

[richard t]

I forgot to mention that i didn't check the small transistors. They are facing the correct way but I don't know how to measure them.

 

[rayma]

Resistors in circuit may not read right. In this case, the LED circuit messes with the measurement.
If possible, lift one end of each and check again. They're probably ok.

Transistors can usually be screened in circuit by the diode function on a DVM, with the board power OFF.
For NPN types, meter will beep when red probe is on the base and the black probe is on the collector or emitter.
For PNP types, meter will beep when black probe is on the base and the red probe is on the collector or emitter.
Test any diodes (regular or zener) the same way.

Hopefully someone who has built one of these can chime in at some point.

 

[richard t]

Well guys. I found my ooops. I had the output transistors swapped. A dyslexic moment. I removed them and put them in their proper homes. Hopefully I didn't apply too much heat but if need be, I'll replace them. The amp powers on with a steady LED. Now onto the biasing. I think this is going to be the hardest thing for me. 🙂 Wish me luck and thanks for all your help. Much appreciated.