Trainer PAD-234A constantly lit up LEDs - need troubleshooting assistance

dl324

Joined Mar 30, 2015
12,931
FYI Pin 1 at 0V, and Pin 2 at 2.5v, the spares seem to jump around irratically between 0-1V on one side and 0v on the other.
The spare inverters have their inputs grounded so the outputs should be around 5V. I'll download a 74HC04 datasheet to see what logic HI should be.
 

Thread Starter

Beave2012

Joined Oct 17, 2015
18
The output seems a little low, but the LED is off so it may be okay. Connect one of the toggle switches (the ones with the paddles), apply 5V (switch up), and measure voltages on that inverter again.
Pin 13 is now at 5V, and pin 12 is at 3.5V. Shouldn't that have been one at 0 and the other at 5?
 

Thread Starter

Beave2012

Joined Oct 17, 2015
18
The spare inverters have their inputs grounded so the outputs should be around 5V. I'll download a 74HC04 datasheet to see what logic HI should be.
Spare inverter (pin 8 and 9 on U3) show 0V on 9, but irratic 0-1V on pin 8. On u4 the spares (8 and 9 again) show 0V on pin 9, and 60mv on pin 8. This is all provided that my diagram for pinout is correct (1 top left and works around counter clockwise)
 

Thread Starter

Beave2012

Joined Oct 17, 2015
18
Measure the voltage on pins 1 and 10 on RN1.
All pins 1-10 on RN1 at 5V

RN4 & RN5 are currently 0V across the entire resistor however.

RN3 - Pins 1-3 5v, 4-10 0V

Getting to be too late and got work in the morning. I will have to continue this en devour tomorrow. Thank you dl324, you've been of great help today! Sorry I can't continue tonight. I'll check on this tomorrow.
 
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dl324

Joined Mar 30, 2015
12,931
Does LED1 really have 3 terminals?

Can you remove U3 from it's socket without having to disassemble anything? If so, you could use the Trainer to test it standalone.

With nothing connected to the LED connectors, I'd expect the corresponding resistors to be at 0V.
 

Thread Starter

Beave2012

Joined Oct 17, 2015
18
Does LED1 really have 3 terminals?
I honestly dont understand about the terminals? it has 2 holes to attach power from the front...

Can you remove U3 from it's socket without having to disassemble anything? If so, you could use the Trainer to test it standalone.
I can try to remove it tomorrow. What should I be looking for after i remove it? How would i test it?

With nothing connected to the LED connectors, I'd expect the corresponding resistors to be at 0V.
Resistors are at 0V all around, forgot I had the LED1 on HIGH so it was getting 5v. (RN1 retested after removing power to LED1 and still 5v pins 1-10)
 

dl324

Joined Mar 30, 2015
12,931
I honestly dont understand about the terminals? it has 2 holes to attach power from the front...
The schematic shows the actual LEDs have 3 terminals.
I can try to remove it tomorrow. What should I be looking for after i remove it? How would i test it?
Put it in one of the breadboards and test each inverter for correct operation.
 

Thread Starter

Beave2012

Joined Oct 17, 2015
18
The schematic shows the actual LEDs have 3 terminals.
Put it in one of the breadboards and test each inverter for correct operation.
OK, pulled the logic inverter (HD74HCO4P), and attempted to test it. I ran 5v into pin 14, grounded pin 7 and then began testing each pair by applying 5v to one of the pair, and measuring the voltage of the other, should be 0. I also grounded one pin, and tested the other in the pair.

When grounded the pair registers around 100mv to 1v, when at 5v applied, the pair shows around 100mv as well. Could this be the issue I am running into? do i just need new inverters?
 

dl324

Joined Mar 30, 2015
12,931
It isn't clear which pin you're applying voltage to and which pin you're measuring. List the test conditions and measurements. For example, for each inverter list the test condition and the measured voltage:
  • pin 1 5V, pin 2 0V
  • pin 1 0V, pin 2 5V
  • ...
Inputs are on the odd pins, except pin 7; outputs are on the even pins, except pin 14.
 

Thread Starter

Beave2012

Joined Oct 17, 2015
18
It isn't clear which pin you're applying voltage to and which pin you're measuring. List the test conditions and measurements. For example, for each inverter list the test condition and the measured voltage:
  • pin 1 5V, pin 2 0V
  • pin 1 0V, pin 2 5V
  • ...
Inputs are on the odd pins, except pin 7; outputs are on the even pins, except pin 14.
Pin 1 5V, Pin 2 .71v
Pin 1 0V, Pin 2 .71v
Pin 3 5V, Pin 4 .74v
Pin 3 0V, Pin 4 .74v
Pin 5 5V, Pin 6 irratic 0-5v
Pin 5 0V, Pin 6 Irratic 0-.5v
Pin 7 = GROUND
Pin 9 5V, Pin 8 Irratic 0-.5v
Pin 9 0V, Pin 8 Irratic 0-.5v
Pin 11 5V, Pin 10 0v
Pin 11 0V, Pin 10 0v
Pin 13 5V, Pin 12 .6v
Pin 13 0V, Pin 12 Irratic 0-.5v
Pin 14 = 5V in
 

dl324

Joined Mar 30, 2015
12,931
Looks like all inverters are bad; I'd replace it. Can you remove the other chip to test (without having to do any major disassembly)?

BTW, I forgot to ask if you knew how to handle CMOS integrated circuits. They're sensitive to static electricity and you should wear a grounding strap. Once you're more familiar with handling them (e.g. not touching the pins), you can get away with grounding yourself before handling.
 

Thread Starter

Beave2012

Joined Oct 17, 2015
18
Looks like all inverters are bad; I'd replace it. Can you remove the other chip to test (without having to do any major disassembly)?

BTW, I forgot to ask if you knew how to handle CMOS integrated circuits. They're sensitive to static electricity and you should wear a grounding strap. Once you're more familiar with handling them (e.g. not touching the pins), you can get away with grounding yourself before handling.
Yeah, i grounded myself to the metal case while moving it around, I am used to it from building PCs from parts. So the 2nd inverter chip seems to have 2 working inverters, and a few that didn't. Problem was that i needed that 2nd chip for the power supply to test. I used a USB power supply to supply the 5v to test on this one. Seems without that chip I cant get any of the voltages to be supplied,even though the LEDs lit up.

*Edit: Replaced the chips into the board and the voltages all work properly, and back to the same issue. Looks like it may indeed be those chips. Time to order from china lol
 
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dl324

Joined Mar 30, 2015
12,931
the 2nd inverter chip seems to have 2 working inverters, and a few that didn't. Problem was that i needed that 2nd chip for the power supply to test. I used a USB power supply to supply the 5v to test on this one. Seems without that chip I cant get any of the voltages to be supplied,even though the LEDs lit up.

*Edit: Replaced the chips into the board and the voltages all work properly, and back to the same issue. Looks like it may indeed be those chips.
Could you post a picture of how you had the chips installed in the solderless breadboard.

You should be able to check the LEDs in circuit with your voltmeter on the lowest resistance range. With the positive lead on the anode and negative on the cathode, it should provide enough current to light the LED; possibly just dimly. If you have a diode checker option, it might work.
 

dl324

Joined Mar 30, 2015
12,931
If your voltmeter has a diode check, you may be able to test the LEDs (in-circuit but power off). My meter will give the forward voltage drop for LEDs with less than 2V Vf. For white LEDs, it lights them, but doesn't give a forward voltage reading. It would even light the white LEDs through their 220 ohm series resistors...
 

Thread Starter

Beave2012

Joined Oct 17, 2015
18
Just replaced both inverter chips. Took a while for them to come in. It now works just fine. No issues. Thank you so much for your help dl324. Now onto the next problem... what are these knobs on the side for.... lol

so much to learn...

Thanks again!
 

dl324

Joined Mar 30, 2015
12,931
Oh I understand the definition of what they do. I am just too new to electronics to understand them.
  • Top knob selects sine, triangle, or square wave output
  • Second knob selects frequency decade
  • Third knob is fine frequency adjust
  • Fourth knob is amplitude adjust
  • Fifth knob is offset adjust
I am guessing I will have no use for these without a oscilloscope though either.
A scope would be nice to have if you're building amplifiers, but you can do a lot of projects without a scope. If you're doing low frequency stuff, there's a free sound card scope program. You could also build a simple logic probe.
 
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