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jetbat 21st October 2011 03:02 AM

Transistor Identification
 
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Hi. I'm trying to identify this surface mount transistor that is part of a piezo buffer circuit. The markings on it are P1KMA. If I search using the first three, P1K, I find the transistor PMBT6428. If I search using the next three, 1KM, I find the transistor PMBT6428L. It looked like this was the transistor but when I looked at the pinout it was incompatible with the way the circuit is wired. The transistor has a single pin on one side and two on the other. The single pin connects to the piezo and needs to be a high impedance connection.

I am comparing two piezo buffer circuits, a old and a new. On the new, the transistor is a Jfet which makes sense because the piezo needs to see a very high impedance. The pinout for this Jfet works with the circuit correctly with the single pin as the gate. The PMBT6428 is a BJT that the pinout would put the single pin as the collector and would put the base to +V. This does not seem right.

If anyone can help it would be appreciated. Attached it a picture of the transistor.

Enzo 22nd October 2011 12:53 AM

Perhaps if you told us the make and model of what it is used in...

jetbat 22nd October 2011 02:20 AM

It's a piezo system by L.R.Baggs that is used in some PRS Guitars. The surface mount componantes are the piezo buffer circuit that is on a pcb mounted under the bridge.

jitter 22nd October 2011 03:46 AM

With SMD-codes you need to differentiate between lower and upper case. Inconveniently, different manufacturers use the same code for different products.
The last letter(s) usually refer to country of origin.

From: SMD marking codes P

p1K = Philips (NXP) PMBT6428
P1 on a SOT23 Philips transistor = BFR92 (also a BJT)
the Philips datasheet mentions only marking P1p (sometimes there are more possibilities if a component is manufactured in more than one country).

but
P1 on a SOT23 Temic-Atmel transistor = SST201 a n-channel jfet
In the context of this thread I would guess that's the one. MA on your transistor might mean Malaysia.

P1K doesn't appear in the SMD codebooks.

jetbat 23rd October 2011 02:47 PM

Thank you.
Yes I did find p1K instead of P1k.

SST201 sounds like a winner. The new piezo circuit has transistor 62P which is MMBFJ201. So both the old and new circuits use the same 201 jfet but from different manufacturers with different codes.


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