So I was looking around on ebay for a power supply because I desperately needed one. Being as I am short of money and can't afford much, I was looking for some deals. I came across a Circuit Specialists rebranded Array 3645A linear power supply. It does 0-36V/0-3A with both CC/CV modes. It also has an RS232 port for PC control, a nice jog wheel for adjusting voltages, a variety of buttons including the ability to do presets. (Un)fortunately for me it was listed as having a blown pass stage and a broken ground banana jack. Now I wasn't quite sure what a blown pass stage meant but when reading up on it the only reference i could find to pass stages were dealing with transistors. So I decided to give the guy a low ball offer (he rejected the first one but accepted the second at $40+shipping). So I figure great, lets see what I end up with.
At worst, even if I can't repair it, maybe the parts inside will be worth the money. This PSU is sold under a few brand names Array, CircuitSpecialist, TekPower and a few others.
So I get the power supply from the box and plug it in, set the voltage to 12.00V, it defaults back to 10.00V. Try a higher voltage, it defaults to 10V. Anything lower than 10V, set just fine. This confused me a bit, and I initially though the logic board may be damaged. I later found out that there is a max voltage function to lock out higher voltages, once that was removed I had the full 0-36V. Anyways, I hook up my trusty UT61E to the outputs and turn the outputs on (it has an on-off button for the outputs on the front, which I like). Uh oh, 60.8V. Change the voltage to 3.000V, 60.8V. Clearly, something isn't right.
Time to open it up!
I see a rather large toroidal transformer, a large filter cap (Nippon Chemicon - 4700uF 100V), the circuit boards and some transistors and a rectifier mounted to a heat sink. The heat sink looks suspiciously like the ones I had on my old P4 processors. The eagle eyed amongst you will notice that I got ahead of myself and already removed the screws for the transistors and bridge. The transistors were held down by a screw with a split washer, a lock washer and an insulator. The bridge was held down by the screw, split washer and lock washer. Almost all of the screws in the device follow this pattern (screw, split washer, lock washer). The thick green and yellow wires are for the safety ground. Basically every single metal piece that is its own part (whether attached to another metal piece or not) is connected AT LEAST once to the safety ground. This was a bit reassuring to see.
The first thing I do is test the transformer. I see isolation between all cables (good) but one cable shows continuity between each wire. At first I think maybe the secondary has shorted, but then I check the resistance and realize that not only does the transformer have multiple secondaries, it also has multiple taps on one of the secondaries (it supplies 4 different voltages, as shown in the second image below). I then proceed to test all of the major resistors and the large filter capacitor. All of these parts appear to be within spec.
Now the sil pad insulators, the tapped holes for the screws and the black connector (i guess a ground to prevent charge build up?) are visible. All of the wires are sleeved in what appears to be some sort of heat/impact protection tubing. It's much thicker and stiffer than heatshrink. The green circuit in the back behind the heatsink is for the RS232 connection to the PC.
Close up of the bridge and transistor. The transistor is a ST TIP35C, the bridge is a Hy Electronic KBU 8D (200V, 8A). Soldering is pretty clean and simple. Not sure why certain traces have solder mask and others don't (heat dissipation maybe).
Now that I have the board isolated, time to check the transistors. One of the transistors shows a dead short between Gate and Source, the other shows dead short between all legs. Since source and gate are paralleled between the devices I remove the clearly dead one. So I can retest the other it checks out as fine (I ended up replacing it anyways later on just to be safe as the source-drain resistance was only 1Mohm whereas the new stock was around 20Mohm). This is the offending transistor.
I broke the leg off post-transistorectomy, its basically a dead short between all three legs (about 2.4 ohms between each).
So I go on a spending spree at Tayda and buy a boat load of stuff: TIP35c, TIP42C, 2sc1815, 2n5551, the various op-amps on the board (TL082, LM329N and JRE4855), the four voltage regulators, plus a bunch of other stuff that I wanted for my component collection.
Since it would take a week for delivery, lets tear this baby apart.
This is the main board removed from the device (the leads are soldered to the front panel unfortunately). The layout is pretty clean, power devices on the left, op amps and related stuff on the right. Soldering is acceptable with no noticeable flaws (leads could be trimmed a bit shorter but thats just me being nit-picky). Note there are 4 leads going to two jacks. Two carry the power, the other two I guess are to sense the voltage at the jack. This means it might be pretty easy to add a couple more jacks and carry the sense connections outside of the case. I'm quite curious why there are so many op-amps (there are 5 single op-amps and 1 double op-amp). I am guessing they are all parts of the control circuitry that I am to much of a novice to understand. Everything else on the board are the required resistors, loads of box caps, voltage regulators, etc. Everything appears to be quality name-brand parts. The relays are from Tyco, the main cap is from NCC, the other parts are from companies like TI, ST Micro etc. The only let down is the various other electrolytic caps besides the main filter, they are all damn Jamicon.
Moving on to the heatsink, we see what appears to certainly be an old P4 heatsink but it does have a Sunon fan (which IIRC from my case modding days is a good company).
So I get the parts in from Tayda and everything looks perfect. I install the new transistors and mount everything back as it should be. Cross my fingers and power it up.
VICTORY IS MINE! Clearly it needs to be recalibrated a bit, especially on the lower ranges. Anybody notice anything odd about the second image? Yep, this PS is rated 0-36V but is actually able to do 0-37V. Lastly, I decided to test it on mV. Testing it out with my multimeter (and no load) it was able to go down to around 1mV but it bounced around a decent amount. I am going to grab a few loads from work (and try those out) see if it stabilizes. Clearly,at 10mV it needs calibration here as well. That being said, they include the calibration software on their website, so that if you have the right equip you can do it yourself. Keep in mind, all of these measurements are basically 5 min after turning it on. When I get the load resistors from work, I will let it have a full hour to warm-up and then test it out.
I'll let others much more knowledgeable than me evaluate the quality of this PSU. I'm just too new to this to really evaluate it properly.