Leader LTC-905 curve tracer issue

[RichardM]

Hi,

I have one f these curve tracers and it has been great to check that transistors are functioning  but it appears to estimate low values of hfe. I have built my own curve tracer to use as a comparison as well using an old analog Sanwa transistor tester. My home built tester and the Sanwa compare well for the same test levels but the Leader tester is always low?

The leader does have an external bias input and if I use that for the base current it compares well with the other 2 testers. I have adjusted the step generator and it looks fine with 0.5V steps up to 3.5V so I am puzzled. It appears when the step generator is loaded through the range resistors, the base current and thus vertical deflection is incorrect.? The base current resistors all measure close to what is required also.

I used my resistor substitution box in parallel with each of the range resistors to see what they would need to be to match the curves using the external bias input and they all need to be dropper to approx 85% of the specified values.

Any suggestions on what may be happening is appreciated.

Richard