Re: re :Magic box build, no sidetone

Jim Kortge

On 4/26/2019 6:31 PM, Kenneth Ketner via Groups.Io wrote:
Greetings Jim:
Hi Ken,

I'm grateful for your reply.
The MB board I am building is marked V1.2B.
That's the latest version of the PCB.

I have a schematic also marked V1.2B. I don't have photo capabilities just now, so I can't send a photo (perhaps later if needed).
I was hoping that you might have a cell phone with camera to take a photo or two of the PCB as it currently exists.

The build passed all the sectional tests in the assembly manual prior to the sidetone section. I hear no sidetone after trying all positions of R32. The manual mentions no keying action. I simply powered up with a 13.8 linear bench supply, no tone with working phones plugged into J6.
Yes, that is correct, no keying, just a steady sidetone upon powering up the PCB.

Q14 and 15 are 2n3904 as supplied in the kit. Q16 is 2N7000.

I get the following voltages.
   Top of R25 and R26 10V; Q14 col 4V, base 1, emitter 0.5V;
That looks right.

top of R28 10V; Q15 col 10V, base 4V, emitter 0.0V ??fault??
Yes, the problem is here.  The base should be at 5 volts and the emitter about 4.3 volts.  It appears that the emitter is shorted to ground directly (solder blob?) and not connected to ground through the 220 Ohm emitter resistor.  The sidetone signal comes off of the emitter to Q16.

; R40 bottom 5V, top 4.9V; R38 top 4V; R37 top 0.0V.

I can send the whole board to you on my dime if that would help.
Well let's not do that yet.  Are there any hams in Lubbock, TX that can help you?  Do you have a good magnifier that you can use to look at the board in the area of R36?  Do you have the ability to unsolder parts without damaging the PCB?  If any of the above get a "NO" answer, then send me the PCB.  Use my callbook address:

Jim Kortge

PO Box 108

Fenton, MI 48430

I'm long in the tooth myself, Jim;>)
It ain't fun sometimes.....  :-)


Jim, K8IQY

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