# Pink Atom Module

#### Seger

##### New Member
Can you recommend where i can buy some 2 SD1071 that works? On the flywheel I just move the wedge track so I fix it! How do you measure if 2SD1071 is ok and with what type of test instrument, what values should you have? Feels like I'm close now!

#### debe

##### Active Member
Its a bit hard to see in the pictures, but the markings are the same on both transistors. But the one on the right is faulty, poor gain & will give intermitent spark or none at all.

#### KeepItSimpleStupid

##### Well-Known Member
In one of the few threads, we discussed another possible substitute.

You can make a quick circuit to measure Hfe. You need a base resitor and a voltage source above 0.6V and a collector resistor to +V. Connect the emitter to ground. Right now, I'm too tired to look at the datasheet and suggest values.

You would measure the voltage across the collector resistor and convert to current i.e. Ic
Measure the voltage across the base resistor and determine Ib
Hfe = Ic/Ib

#### Skelle

##### New Member
Thank you Debe, it reasures me that i’m not going mad completely. Fancy tester the second one. First one is similar to the one i found on eBay for 12\$. Tried some other darlingtons, but same result both in the tester and the circuit. The Solex flywheel have 4 magnets, which makes it somewhat special. Waiting for some other transistors. Didnt expect rocketscience with a circuit that contains only 5-6 components. Very strange i must say. Also tried the ‘birdnest’ config ie no PCB involved, but it didnt change the result.
Oh forgot to say, the original darlington i tested, also says ATOM - A1, and Philipnes...spelled that way. Besides a number 403C422. Also this logo that looks like 13 or 73

#### Skelle

##### New Member
Could there be an explanation in the Uf readings? It seems that the original Atom darlingtons have Uf above 1 Volt, where the HFe readings are moderate to low. Anyone have a good explanation to what can be learned from these readings. I mean, as we are dealing with pulses, the amp gain effect are maybe secondary to a higher Uf (voltage forward)???...just a thought

#### KeepItSimpleStupid

##### Well-Known Member
datasheet is here: http://www.ges.cz/sheets/2/2sd1071.pdf

there are two B-E junctions in series. That would suggest a V(b-e) of around 1.2V.
V(b-e)(Sat) is 2V from the datasheet.

Saturation values are often different when the transitor is used as a switch or amplifier. Note the curves for the saturation voltages..

The graphs also show that you need Ic to be 50 mA to show an Hfe of 40.

At Ic = 2.5 mA, Hfe might well be 8 Usually Vbe is more indicative of bad in my experience with bi-polar transistors.

#### Skelle

##### New Member
datasheet is here: http://www.ges.cz/sheets/2/2sd1071.pdf

there are two B-E junctions in series. That would suggest a V(b-e) of around 1.2V.
V(b-e)(Sat) is 2V from the datasheet.

Saturation values are often different when the transitor is used as a switch or amplifier. Note the curves for the saturation voltages..

The graphs also show that you need Ic to be 50 mA to show an Hfe of 40.

At Ic = 2.5 mA, Hfe might well be 8 Usually Vbe is more indicative of bad in my experience with bi-polar transistors.
My tester uses a 9volt battery, so maybe i should use a dc power supply. I’m still puzzled to why the original transistors show Uf above 1volt, and also what possible difference it would have in this config.

#### Skelle

##### New Member
My tester uses a 9volt battery, so maybe i should use a dc power supply. I’m still puzzled to why the original transistors show Uf above 1volt, and also what possible difference it would have in this config.
Forgot to say, used a BU910 as test...same result and same measures in the tester. One of my friends have a small supply of Darlingtons, so going to test some other models. Debe...you wrote that you tested some as well? Do you remeber the types?