AV- is only -.67v
TP22 voltage is good, at 3.33v.
JP3 and JP4 are both shorted.
Screen lights up and shows oscillator grid and figures.
Switches seems to be working fine, altering figures/words on screen.
No signal seen when touching red clip with finger.
Voltages match closely for "AV+," +3.3V," and "+5V."
V1 is 4.2v. V2 is 3.44v.
All resistors are properly placed.
(However, I did not check resistors individually for resistances.)
All capacitors are properly oriented.
All transistors are properly placed.
All solder joints look good.
A few other voltages are wrong too.
When connecting a known operational signal generator, no signal is detected on the DSO138 screen.
Please help.
AV- is only -.67v
Re: AV- is only -.67v
Hi slantsix,
The -5V is produced by the circuit of Q1, Q2, and U4, in the right side of the "Power Supply" section..
You need a square signal at the base of Q2, check with a scope. That square signal is produced by the processor, it is VGEN, check that one too.
You also need the +8.6V at the emitter of Q1. The actual voltage depends on the "raw" input voltage to the board, +8.6V is in case you feed 9V to the board.
After the D1 diode you should see -8.1V as indicated on the schematics. You should see the same voltage at TP25 too.
The -8.1V is regulated to -5V by U4, a fixed -5V three-point regulator.
You should be able to follow these voltages easily.
BTW, in my kit there were quite a few excess resistors, so I did measure every resistor before installation.
You should also check if the electrolytic caps were installed with the right polarity, a reverse installed electrolytic cap would "short out" these voltages.
Regards, Peter
The -5V is produced by the circuit of Q1, Q2, and U4, in the right side of the "Power Supply" section..
You need a square signal at the base of Q2, check with a scope. That square signal is produced by the processor, it is VGEN, check that one too.
You also need the +8.6V at the emitter of Q1. The actual voltage depends on the "raw" input voltage to the board, +8.6V is in case you feed 9V to the board.
After the D1 diode you should see -8.1V as indicated on the schematics. You should see the same voltage at TP25 too.
The -8.1V is regulated to -5V by U4, a fixed -5V three-point regulator.
You should be able to follow these voltages easily.
BTW, in my kit there were quite a few excess resistors, so I did measure every resistor before installation.
You should also check if the electrolytic caps were installed with the right polarity, a reverse installed electrolytic cap would "short out" these voltages.
Regards, Peter