ECC Power Stage transistor measurement using a transistor tester

Post by **jreed** » 12 Oct 2017, 16:57

I bought a little transistor tester kit and made a couple in-circuit measurements of the power transistor inside the ECC blower motor control unit.

: Transistor tester gizmo

The transistor is part of a much larger circuit that is built into the base of the unit. The transistor is a power MOSFET that is attached to the PCB with pads labeled "G S D" for Gate, Source and Drain.
The pictures below show how the leads were connected to the transistor pins:
Side view:

: Clips attached to the G, S and D of the transistor -- side view

Edge view:

: Edge view of the clips attached to the G, S and D of the transistor

I tested two units that I suspect are good -- I removed them from junkyard Volvo 850's with ECC systems.
The two units both tested as NPN transistors instead of as MOSFETs, with the Gate being reported as the Base, the Emitter as the Source, and the Collector as the Drain. They reported as having forward voltage of about 0.48V and B=3. B is typically the gain metric for a bipolar junction transistor like an NPN.

Unit A test result:

: Unit A result

Unit B result:

: Unit B result

I thought I would share this result in the hopes that it might help someone figure out if they have a bad ECC power stage, and also to see if someone might have a burned out unit that they might want to send me for testing, to see if this transistor tester can tell a good unit from a bad unit.

Post by **scot850** » 12 Oct 2017, 23:13

If no one takes you up on the offer, I can ship you a bad unit. It is expensive to ship from Canada, but in the interest of learning I would do it. Hopefully there is someone nearer to you with a bad unit.

Neil.

Post by **abscate** » 13 Oct 2017, 05:45

I'm amazed the MOSFETs are labelled but if you can find the component label the data sheets are always on the web.

I'm sure root failure is usually MOSFET burnout, I don't know why I'm Sure of that but if I mansplain it that makes it true.

Post by **scot850** » 18 Oct 2017, 17:36

How did you get on with the testing? Did you get a dud unit at all? If you get this test process up and running, I would be interested in buying a test rig from you to test the ones I have in the stash (about 5 of them from V/S 70's). Those 5 have been 'tested' in one of my cars by substitution and just varying the speed controller manually and all did this fine. I am hoping that is a sound way to do a basic test of it works or not! But if there is a more exacting test method like yu are working on I would be interested to know more.

If you don't get any offers of a dud to work with I have one, so fell free to PM me your address and I'll post it too you.

Neil.

Post by **jreed** » 19 Oct 2017, 05:31

I think the in-car operational test you described sounds more complete and helpful than what I did with the transistor tester. I actually built the transistor tester for general purpose testing of small components on the bench... capacitors including equivalent series resistance, transistor pin identification and gain, LEDs, diode forward voltage etc. It works pretty well for those purposes. I just thought I'd test it out on the two ECC power stages I picked up a couple years ago to see what it could do.

PeteB · Post by **PeteB** » 19 Oct 2017, 07:33

Interesting, I take it you bought a kit tester? Which one?
It is probably seeing either diode or transistor junctions connected to the FET
and those are "confusing" it. Might be a good enough test but testing a dead
should help confirm it.
Semiconductors are very reliable as long as they are not stressed by over voltage,
current, or power. Heat and thermal cycling kills them.
If that part is prone to failure the the power FET probably needs a heat sink.
Also, electrolytic caps dry up with age, we are lucky if they are good after 20 years.

Post by **jreed** » 19 Oct 2017, 17:11

Agreed! Part of the reason I bought the little kit was to test electrolytic capacitors for high ESR.
The kit I bought was the 2016 version of the EZM328, which uses the Atmel ATmega 328 microcontroller. It has a rotary control, probe pins and a ZIF test socket, and a large LCD screen. It was $13 on eBay delivered from China. I like it.

Post by **sleddriver** » 20 Oct 2017, 18:03

The board of the one I pulled is similar, but different, to the one pictured. Mine is 9166694 (99WO4). Another # is 99G69376. ALPS made in Japan. On the PCB is ANJ971014C. This unit features a large, black ZNR to absorb the motor back EMF and few elec. caps. Not sure if it works (PNP last trip), however testing it using the car is straight forward.

Testing a power MOSFET is a bit different than a BJT, as the former is a voltage controlled device (Ids varies with gate voltage) while the later is current controlled (Ice varies with base current). Thus, the MOSFET driver ckt is different than a BJT. Further, it has to account for and drive the gate capacitance where the gate impedance is very high.

Finally, before testing or touching probes to pins, be sure to discharge yourself first. It's quite easy to destroy any FET by static electricity.

TeraWales · Post by **TeraWales** » 10 Apr 2019, 11:43

Hi...if you grab a plane-Jane 1N4004 diode, for instance, set your meter for a diode test, and connect the positive lead to the anode and the negative lead to the cathode (the side with the band). You should read about 0.45V to 0.65V or so, depending on the amount of current that your meter feeds through the diode. Reverse the leads with positive on the cathode and the negative on the anode, and you should read an 'OL' or 'Overrange'...check the documentation on your meter to better understand how it will indicate an open circuit, but essentially there should be no conduction with the leads reversed. A shorted diode will show '0V' with the leads in either orientation.

Post by **Ozark Lee** » 13 Apr 2019, 08:06

The original MOSFET is no longer available and it hasn't been for years but there are some sort of close substitutes. A guy over on XCForums experimented with a few current versions and got a couple of what were then current production devices to work similarly to the original. Not exactly the same characteristics but close enough.

Particularly with MOSFETs it seems like they have an available life of about 10 years after which you are screwed. This is particularly true in the devices for RF and it is a real irritant when you have a quarter of a million dollar radio or TV transmitter that won't run because you can't buy a stinking $20.00 part. Even after being clever enough to engineer around the bad part it costs a fortune to get the thing running again.

...Lee