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LakeShore 330 temperature controller

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Does anyone here have a schematic diagram over a vintage LakeShore 330 temperature controller, or could otherwise tell me what component Q6 used to be?

I "fixed" the controller last week, where an OPA541 power opamp had blown out its magic smoke and it worked again for a couple of days, just to then burn up a TO-220 device on the same heatsink. Of the type number only the last two digits remain legible: ...15

Since its right leg was connected to the positive rail of the power opamp and since all other TO-220 parts inside are voltage regulators (plenty of them) I falsely assumed it must have been a 7815 - in the hindsight quite clear that it could not have been... :palm: - but I was proven wrong by a small explosion...  :-BROKE

7915, negative reg, not positive reg 7815 ?

Grab the datasheet for both, check the pinouts and typical application schematics.

Sometimes a pic of both sides of the PCB can help us......


--- Quote from: tautech on September 10, 2016, 07:49:39 pm ---7915, negative reg, not positive reg 7815 ?

Sometimes a pic of both sides of the PCB can help us......

--- End quote ---

I thought of the 7915 as well, but it does not make sense either at this position. Also as I saw later all 78xx and 79xx are labeled as Uxx on the board (as they should), while the burned part was Q6. I suppose it might have been a MOSFET like an "...N15" or "...P15"

Let me rephrase my question:

After a more detailed analysis of the traces and connections around the burned Q6:

Is/Was there a power NPN transistor around in the mid-1990s:

* TO-220 package BCE
* part number ending in 15
* VCEmax > 60V
I am now quite sure that the transistor was part of a discrete voltage regulator with two zener diodes as references (1N5363 alone and 1N5363+1N5360 in series). The switching between the two ranges was done through a relay which also switched between two taps on the mains transformer.

The BCE pinout it the normal one for TO220 transistors. So plenty of transistors to choose from.

For the BD series, there are some types with subtypes of -40 / -25 and -15. There might also be 2Nxx15 or 2SCxx15.


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