2SJ55 testing as Depletion Mode but are actually Enhancement Mode devices

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I'm repairing a Tandberg 3006A amp. It uses 2 J55 and 2 K175 MOSFETs for the outputs on each channel. On each channel, one of the J55s tests as Enhancement Mode (it should). The other J55 in each channel tests as Depletion Mode. These are in the same position. I'm using a Peak Atlas DCA Pro for the testing. Does this represent a problem? I hope not because the J55/K175 are no longer made. I think Exicon makes a replacement but can't remember the numbers.

Thank you.
 
Exicon TO3 devices are ECF10N20 and ECF10P20 for n-channel and p-channel respectively, profusionplc.com stock them Exicon Lateral MOSFETs Lateral MOSFETs (Buy Online) | Profusion
[ And yes they are case == source ]


Laterals tend to have very low threshold voltages which could conceivably drift across 0V with ion-migration over time, or the device is toast of course.
 
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Exicon TO3 devices are ECF10N20 and ECF10P20 for n-channel and p-channel respectively, profusionplc.com stock them Exicon Lateral MOSFETs Lateral MOSFETs (Buy Online) | Profusion
[ And yes they are case == source ]


Laterals tend to have very low threshold voltages which could conceivably drift across 0V with ion-migration over time, or the device is toast of course.

Thank you for this information. The explanation is helpful, as is the source for the Exicon.
 
In some cases, if the gate on the mosfet is left open, it will float up enough to turn the device on. This is probably especially true for lateral devices, as they tend to have lower threshold devices than vertical fets. I encountered this when testing a batch of Semelab TO-3 devices I received recently. I was testing them with a DVM to make sure they were really lateral devices (case connected to source). When measuring from drain to source, the mosfet would conduct like a depletion mode device and look like a short to the DVM. Shorting the gate terminal to the case (source) with the meter probe cleared this up, and the device would test (as it should) as an open circuit.
 
ECF10N20 DCA tested to be depletion mode

Recently i build an Arduino controlled power amp based on the Elektor Crescendo since I had the original Hitachi 2sk/2sj mosfets hanging around from a previous build of the same amp in the '80s. It is working flawlessly so I decided to build another one based on the same design but using the ECF10P20/ECF10N20 mosfets from exicon. So I purchased them since the manufacturer claimed that these are replacements for the 2sk/2sj's.



When measured with an Atlas DCA Pro the ECF10N20 is stated to be depletion mode and not enhancement. The 2sks/2sjs test ok both as enhancement as well as the ECF10P20.



Any ideas ?? Is it possible the manufacturer did a blunder on the ECF10N20 mode ??
 

PRR

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> Atlas DCA pro doesn't like lateral fets with low Vgs.

And it may be looking for much smaller current than a big power FET's happy-zone. I have seen 100uA at Vgs=0, which could be a very small enhancement device or just leakage in a very large depletion device.
 
The real test will follow

Thank you for all your replies. The fact is that 2SK135 tests ok and correctly indicated as an enhancement mode device whereas ECF10N20 tests ok but is indicated as a depletion mode device.



The real test will be the replacement of the power mosfets from a power amplifier module currently working perfectly fitted with 2sk/2sj devices with the ECF10N20/ECF10P20 devices and check if still the module will operate as expected.



I will have a go to this within the next two weeks (vacation time in Greece) and i will post the results.
 
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I did that very thing with replacing Hitachi original TO3s with Excicons. It worked wonderfully. I don’t have a scope or technical measurement equipment, but I’ve been very very pleased with the outcome.

Hafler DH-200/220 Mods

Good luck!
 

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