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  1. (*steve*)

    Successful Stanford Research SR530 lock-in amplifier repair

    I didn't have a 0.25W 20Ω resistor, so I put two 10Ω 0.125W resistors in series. This is what it looks like Now for a bang test :-)
  2. (*steve*)

    Successful Stanford Research SR530 lock-in amplifier repair

    R138 looks suspicious. And doesn't measure 20Ω any more (it appears to be open) Did one of the tantalum capacitors fail which probably caused almost the full 18V to appear across this (or have about 100mA flow through it). Let's see... 100mA would be 0.2W (and it wouldn't have fried - is...
  3. (*steve*)

    Successful Stanford Research SR530 lock-in amplifier repair

    The voltage across the various big caps are: C107, 1.5V C108, 2.5V C125, 1.135V C126, 0.87V Well, that's not going to stress 16V caps. What about the regulators input and output voltage (btw, they're not hot) And the voltages around the 78L15 are close to zero (actually -0.6 at the output)...
  4. (*steve*)

    Successful Stanford Research SR530 lock-in amplifier repair

    And it looks like I have yet another problem. The reference input works fine, but the signal inputs don't do anything at all. If you remember from the very beginning, the input circuitry is under a large shield, so off that comes! Here is a portion of what is under that shield, near the...
  5. (*steve*)

    Successful Stanford Research SR530 lock-in amplifier repair

    Curiously, the unit was still listed on their September 2016 price list. And, the manual I'm using is this one. If you're just hanging out for a lock-in amplifier, try this, or this.
  6. (*steve*)

    Successful Stanford Research SR530 lock-in amplifier repair

    The manual states the following: Power Supplies The line transformer provides two outputs, 40VAC and 15VAC, both center tapped. The transformer has dual primaries which may be selected by the voltage selector card in the fuse holder. The 15VAC is rectified by diode bridge BR2 and passed to 5V...
  7. (*steve*)

    Successful Stanford Research SR530 lock-in amplifier repair

    Well, since I had to get the voltage regulator, I thought I would get a new comparator too. The new regulator, resistor, and replaced cap. And the socketed LM311 with the nearby tantalum replaced with an electrolytic. This is the second shorted tantalum I've had in a couple of weeks. I'm...
  8. (*steve*)

    Successful Stanford Research SR530 lock-in amplifier repair

    I've traced the short to near an LM311. And it wasn't that, but it was a tantalum cap near it. Ok. Time to replace all the suspect parts. I think I'll replace the LM340T15 (AKA 7815) and the 10Ω resistor, socket the LM311, and I think the two tantalum caps will get replaced with electrolytic...
  9. (*steve*)

    Successful Stanford Research SR530 lock-in amplifier repair

    That cap has a resistor in series with it which measures 1.70Ω. Even if it's that cap, I'm seeing way less resistance. And, it's not actually tied to the output of the regulator. I'm still reading a low resistance (under 0.5Ω) across the output of the (now removed) regulator. The good news...
  10. (*steve*)

    Successful Stanford Research SR530 lock-in amplifier repair

    About to remove a suspicious tantalum cap. There's the back-lit PCB. There are TO-220 size pads for the regulators. And seeing that, I've spotted another 2 regulators! And that cap was fine... Trying the regulator next. Nope. Hang on a sec. Does that blue capacitor look unusual? (And...
  11. (*steve*)

    Successful Stanford Research SR530 lock-in amplifier repair

    Well, minus the diversity receivers, maybe. A lock in amplifier acts as a very narrowband filter that is tuned by a reference signal. The "narrowness" of the filter can be enhanced by increasing the integration period, at the expense of being able to detect more rapid changes of the input...
  12. (*steve*)

    Successful Stanford Research SR530 lock-in amplifier repair

    What mystery? All you need is a glove and a piece of string!
  13. (*steve*)

    Successful Stanford Research SR530 lock-in amplifier repair

    According to the manual I'm reading, there are at least 14 3-terminal voltage regulators in this unit. And I've only found 7. The manual has a parts list but no schematic. The parts list is actually reasonably useful, listing actual part numbers for semiconductors, and tolerance/stability for...
  14. (*steve*)

    Successful Stanford Research SR530 lock-in amplifier repair

    Or did you mean the actual puppy? That's an approximately 8 year old papion, an ex-grand champion show dog (and not the sort of show dog that rounds up sheep) She is the dog that my wife just paid $4000 for a knee operation on. That makes my hobby look cheap!
  15. (*steve*)

    Successful Stanford Research SR530 lock-in amplifier repair

    What's the chance? One of the +15V regulators measures 0.35Ω between output and ground. All the others are several kΩ. And there's some of those evil tantalum capacitors! Is this going to be a case of deja vu? U904 (the one on the right) measures 0.35Ω from ground to output. Is one of...
  16. (*steve*)

    Successful Stanford Research SR530 lock-in amplifier repair

    And the voltage between CT and 5.6 (the board is marked 5.6 CT 5.6 where the other three wires from the transformer go) measures 17VAC! Is that 5.6 or 56? But it certainly isn't either (if that means volts) If you look at the earlier images, you'll see a large heatsink (it's about 80mm tall)...
  17. (*steve*)

    Successful Stanford Research SR530 lock-in amplifier repair

    Oh no! But, but, but... I'm going to service it. Does that mean I can't use it afterwards?
  18. (*steve*)

    Successful Stanford Research SR530 lock-in amplifier repair

    Stanford Research SR530
  19. (*steve*)

    Successful Stanford Research SR530 lock-in amplifier repair

    Interesting. With a 200VAC input voltage and the 12VAC reading 11.7VAC, there seems to be insufficient voltage to some other rail to allow the front panel LEDs to illuminate. At this voltage the unit draws approximately 250mA, which is also the recommended (slow blow) fuse rating (and about...
  20. (*steve*)

    Successful Stanford Research SR530 lock-in amplifier repair

    Ok. Happy to turn it on... Looks fine and the buttons respond in a way that seems to be correctly. I think I'll leave further stuff until I've read the manual :-) Hmmmm.... There's a bit of a funny smell. It's the "transformer" smell. The 12VAC marking on the board (direct from the...
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