One of the thunderstorms recently apparently *also* took out the power supply of my TLA614. Which I leave in standby all the time due to the options data likely being in a Dallas sealed battery-backed RAM chip, in which the battery is sure to go flat soon.
Today I was rearranging my workbench layout. New arrangement of equipment. At the end, to check everything was correctly plugged in (new mains cord layout), I turned everything on. Except the TLA, which wouldn't. Quick check: both mains fuses blown. Replace fuses, try applying small V via variac. Lots of current draw with just a few volts. Great.
Taking the machine apart, it turns out the power supply comes out very easily. The whole thing is on one tray, after removing some connectors and a few screws it slides right out, even with the mains IEC and fuses attached.
Didn't take long to find a fault: one of the two FDA24N50 FETs in the input PFC stage is a dead short. But... getting that out was not so nice. One that really illustrates how far Tek have fallen.
Firstly, they contracted out the entire power supply design. The silkscreen says: "Designed by: Martek Power Inc."
http://www.martekpower.com Sticker:
Model: PS2251 Rev F
P/N: 119-5806-02 Rev 2
SN: 1195 - 2000
IN: AC 100-240VAC 50/60/440Hz 6A typical
OUT: 3.35VD/35A 5VD/22A 12VD/6A Vfan/2.5A
5VSB/1A 380W maximum.
Well, there was zero chance of getting a schematic from Tektronix, and I suppose from Martek is also zero. Search on their site turns up nothing.
Also Martek don't care about serviceability at all. The PFC FETs cannot be removed without also removing their heatsinks from the PCB. And the heatsinks are soldered into the PCB and are impossible to remove from the PCB without massive heat capacity custom soldering head applied to the pins. Which are thick copper tabs, pressed into tight, non-round holes, then twisted over on the solder side, then soldered.
Fortunately I had my massive heat capacity custom lump-o-copper soldering tool.
Even with that the heatsinks had to be levered out, and pulled through-plating out in 4 pads out of 8 due to being such a tight fit even with solder molten.
It also turns out the through plating on _those_ holes is circuit-functional, so when putting this back I'll have to be careful to jumper and solder both sides - on these heavy copper heatsinks.
Now I have a question. There are plenty of FDA24N50 available on Aliexpress, and even some from au.element14.com (via stock in England.) But does anyone know of somewhere in Sydney I can buy 2 or 3 tomorrow (Monday)? I don't want to have the TLA sitting around in pieces for weeks while an Aliexpress order filters through the post. Especially since I found it was dead, and opened it up, only minutes after opening up an old scope to fix some minor problems it has.
Fingers crossed that FET is the only fault. Because if it's much more, and there's no way I can get a schematic, I don't fancy my chances of fixing this.