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Old 21st October 2011, 04:02 AM   #1
jetbat is offline jetbat  United States
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Default Transistor Identification

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.
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Old 22nd October 2011, 01:53 AM   #2
Enzo is offline Enzo  United States
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Perhaps if you told us the make and model of what it is used in...
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Old 22nd October 2011, 03:20 AM   #3
jetbat is offline jetbat  United States
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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.
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Old 22nd October 2011, 04:46 AM   #4
jitter is offline jitter  Netherlands
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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.

Last edited by jitter; 22nd October 2011 at 04:56 AM.
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Old 23rd October 2011, 03:47 PM   #5
jetbat is offline jetbat  United States
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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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