Tek 5441 Scope


Does anyone have a source for Q910 part number 151-0331-00 or 151-0496-00 or a cross reference it appears to be an NPN darlington transistor. R911 on the power supply board is getting very hot, and Q910 appears to be shorted. Thanks


Good day,
Walter with Sphere seems to have some available; 
But unless my memory fades me, this is a simple darlington npn transistor; which I have replaced with a type TIP122 in an older repair. That type is commonly available; i.e. made by ON Semi to date.

Good luck with your repair,
Does anyone have a source for Q910 part number 151-0331-00  or  151-0496-00 or a cross reference it appears to be an NPN darlington transistor.  R911 on the power supply board is getting very hot, and Q910 appears to be shorted.    Thanks


Did you try Sphere Research Corp. Website or phone 250 769 1834 also look for bad resistors before replacing the transistors. I wrecked 2 transistors and found that a resistor had cooked, loosing 80% of its resistance.


According to the TEK Cross Reference pg. 6-21:

151-0496-00 crosses to a D40K2, which is available from MOUSER their p/n 610-D40K2 @ $3.47 each with 348 in stock.

151-0331-00 crosses to a D40C5, which does not show available.

Good Luck!

Michael Lynch
Dardanelle, AR

Stefan Lindberg

Good Evening

I've got a 5440 myself so the power supply is the same.

If Q940 is working and considering that this is a simple regulation job, I would remove Q940 and measure its hfe and take a similar Darlington NPN with some margin in U/I.

The issue might rather be to fit a model that does not have the special casing since the transistor is squeezed in place for cooling as standard. However, since we are talking about regulation only, then why not take a beefier Darlington and connect it with short wires and mount it to the case.


I recently fixed up a 5440 power supply, so here's what I've learned.

First, be sure there aren't any shorted Tantalums on the output side. you might also need to lift the wire to the load to be sure there is not a short on another board.

Second, R911 and similar resistors in the other supplies are parallel to the pass resistor, sharing some of the load current. This is a really nasty idea when it comes to troubleshooting. With insufficient load the output voltage will rise to the raw input voltage even though the pass transistor is cut off. I put a load resistor on the supply to prevent that. When it's finally fixed, plug in the modules before setting the regulation voltage. The good news is that apparently the load circuits can tolerate the greater voltage without damage.

For the transistor, pull it from the circuit and check its gain and bias voltage. Mine had one that part of the Darlington pair worked and the other part didn't, giving a seemingly working transistor but with low gain and a single junction instead of two in series. I used MJE800, still common and available from Digikey.

Finally, I agree with the post about checking the small resistors. Mine drove me crazy and I almost said the heck with it and threw in a 3-terminal chip regulator. I finally found one resistor of the precision pair that sets the reference voltage had gone open, after lifting one end of most of the small components in that circuit.

Good Luck.


Thanks, I've been working up a Mouser order for a few days and added this to it and sent it off...


lists...Thanks for that explanation, I'd stared at that circuit for some time. I've always been a user of test equipment in two way radio and broadcast mainly, since retired. About a year ago I fell heir to about 6 pickup truck loads of Tek equipment from a friend that passed and this is a whole new experience.