Electronics > Repair

LakeShore 330 temperature controller

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uwezi:
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

tautech:
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......

uwezi:

--- 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"

uwezi:
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.

Kleinstein:
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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