Thaikit transistor curve tracer help

[akabek]

I assembled a curved tracer and power supply kit offered through Thaikits.  I believe you can also buy it on ebay.

https://www.thaikits.com/index.php?option=com_virtuemart&view=productdetails&virtuemart_category_id=19&virtuemart_product_id=595

When I connect a working transistor to the curve tracer and a scope I only see a straight line.  I do not see the stepped curves.  I am a beginner when it comes to electronics but there are two ICs on the board.  Do they provide the stepped curves?   One chip is the Op Amps TL074CN and the other is a  Counter ICs CD4024BE.  The manual for this kit does not provide voltages so I am not sure how to check if they ICs are faulty.

I attached a pic of what I see on the scope and the manual shows a schematic.  Any suggestion?

[TERRA Operative]

First up, you have checked your supply voltages to the PCB, and double and triple checked component orientation and that the correct parts are in the correct locations? Also, have you checked for bad or missed solder joints?

I have one of these kits working, so can take measurements as needed.

[akabek]

When I initially assembled the kit it was working but the curves were not sharp, picture attached.  From the PCB board to the front panel connectors I was using regular 24AWG wire.  Hoping to correct this I replaced the standard wire with shielded wire and now I only get a straight line.  I figured the shield cable was causing the issue so I put the 24AWG wires back and no change.  All I get now is a straight line.  I checked the diodes, caps, resistor and transistors and they all look good.  I also re flowed the solder at each leg and confirmed the PCB is receiving the required 15+/- V from the power supply board.

[akabek]

I took a picture of the scope with both X/Y channels connected, only Ch1 - X and only Ch2 - Y.  When only Ch2 - Y is connected there is a very short line, in the picture it looks like a dot.  I am not sure if this helps at all.

[TERRA Operative]

I had the same issue with shielded cables. It seems the increased capacitance of the shielded cable causes problems.
Some ferrite beads and short unshielded cables works on mine.

[akabek]

Right now whether I use shielded or regular wires all I see is a straight line in XY mode.  Prior to switching to shielded wires I did see the stepped curves.

Any chance you can take some voltage readings around the relays and the ICs?  I have checked all the other components.

[Calambres]

I had the same issue with shielded cables. It seems the increased capacitance of the shielded cable causes problems.
Some ferrite beads and short unshielded cables works on mine.

Ditto, ditto and ditto

Shielded cables lead my kit into problems. It was not until I shortened my unshielded cables and used ferrite beads that my Thai kit was able to perform correctly.

[akabek]

I have not used ferrite beads.  Would I just add one per wire or multiple?

[Calambres]

I kept adding beads untill all artifacts disappeared. Seem to recall about two small beads per wire 

[Calambres]

By the way, the files below may help you.

First is the schematic and the second is the original ELEKTOR project it is based upon. I installed the 4/8 traces switch included in the original project.

[akabek]

I kept adding beads untill all artifacts disappeared. Seem to recall about two small beads per wire 

I will leave the standard wires in and add some ferrite beads.  Did you add the beads to the X, Y, E, B and C wires?

Nice setup.  Are you able to measure up to 4 transistors at a time?  If so how did you wire that up with 1 DUT on the PCB?  This may be a silly question but I no experience around the design side.

[Calambres]

Did you add the beads to the X, Y, E, B and C wires?

Just C,B & E wires.

Are you able to measure up to 4 transistors at a time? 

Nope, up to 6 transistors  Ideal for comparing and matching.

If so how did you wire that up with 1 DUT on the PCB?  This may be a silly question but I no experience around the design side.

With a 7 way switch, selecting sequentially from 0 (no connection) and 1 to 6.

[akabek]

The the additional switch is definitely a very handy option.

[akabek]

I picked up some ferrite beads and installed two on each C,B,E wire.  They also had the CD4024 and TL074CN IC so grab those.  After installing the beads, and swapping one IC chip at a time, I still do not see the stepped curve.  I also went over all the solder joints with the iron and still no luck. 

I have a feeling my issue may be around the signal from the Y channel.  I was probing for continuity with the meter and when I check the X channel to ground whether it be on the PCB or the BNC connector there is no continuity.  But when I checked the BNC connector and PCB board with the meter I found the Y contact has continuity with the ground contact.  Is this correct?

[akabek]

Well I feel silly.  Changing my wires around I swapped the E and B wires.  I now have it working and the traces are more sharp than before with the beads installed.

[TERRA Operative]

Nice. I was about to pull mine off the shelf and start probing. Good to see you got it going.

[akabek]

I am looking over the manual provided for this curve tracer.  It does not show how to calculate the mA per division.  The screenshots show ch1 set to 2v and ch2 set to 20mV.  If I use these settings does this calculate to 20mA per division?