840AV dead PSU

[pl212]

I mean this very kindly, but please be very careful. You are now up to three or four "fireworks" events, and it's very important to remember you are dealing with voltage which can easily kill or maim you. I think you should seek out a known-good power supply from a seller on eBay and let other areas of this computer be where you experiment and learn.

 

[imactheknife]

I mean this very kindly, but please be very careful. You are now up to three or four "fireworks" events, and it's very important to remember you are dealing with voltage which can easily kill or maim you. I think you should seek out a known-good power supply from a seller on eBay and let other areas of this computer be where you experiment and learn.

I used a psu from an 8500 / 9500. Recapped it, works great in my q840

 

[Byrd]

I mean this very kindly, but please be very careful. You are now up to three or four "fireworks" events

Think once you start playing “whack a mole” to 240V PSU components it’s time to call it a day. Even if working would you trust it? Maybe see how well you can shoehorn a decent quality ATX PSU into the existing case.

 

[grieverheart]

I successfully created an adapter for the ATX power supply and it works very well! Now, the original PSU also has output AC. Inside the PSU there is a relay which is operated by the 12V rail, which turns on the AC output. I also ordered a similar relay to possibly keep the functionality. If anyone has tried this before and has any tips, please let me know.

I also wanted to try to repair the original power supply so I had ordered some components. One of the components I found that was faulty, was a TRIAC, which appeared shorted. I also ordered couple of MOVs to replaced the blown ones. I couldn't read the MOV markings anymore, so I ordered these, but now I'm wondering if they are the correct ones. Unlike the usual case where they are placed before the bridge rectifier, these are placed next to each of the two main capacitors.

In any case, I replaced the TRIAC, replaced the main capacitors, replaced the MOVs, jumpered the fuse temporarily as I didn't have a replacement at hand, and I also created a light bulb current limiter. I plugged the PSU in the current limiter and turned on the current limiter switch. Nothing blew! The light bulb was dim. I checked the voltage on the main capacitors and it read about 200V. Then I decided to attach the fan, and after turning on, I saw sparks and smoke somewhere in the area of main capacitors, but I couldn't tell which component got burned! After that, the light bulb was full on...I'm not sure if the fan caused the issue or it was just a coincidence. Also, I would expect some short, but measuring the resistance between the AC leads show something like 200k Ohm, so now I'm not sure what is wrong. I checked all diodes on the main side and they all seem to give correct values. The bridge rectifier also does not seem to be bad. Does anyone have any tips? The only thing I can think of now is to start removing components and measure them off circuit. As a last resort I'm thinking of buying one that is working and cross reference the circuits.

 

[Byrd]

You're flogging a dead horse here if this is the ... fifth ... reported sparks, smoke, fireworks on the same PSU? Please be careful, save your time and money buying random components, hope you find another one.

 

[joshc]

Does anyone have any tips?

yeah, please stop trying to fix a power supply when you have no idea what you’re doing. It’s dangerous.

 

[grieverheart]

Well, I didn’t expect this type of reaction. I thought people here shared my passion for repairing things.

It’s not like I know nothing about electronics, and PSUs in particular, this is just the first time I’m trying to repair one myself. Obviously I made some mistakes at the beginning, but sometimes you have to take a risk and turn the thing on. You are never going to be sure you have repaired it until you see it working, and that means there might be more sparks.

Anyhow, I personally like the challenge, and up to some point I don’t might spending extra money if I learn something at the end of the day. The feeling of managing to repair something is priceless.

The PSU is definitely not beyond repair. Despite the “fireworks”, there is only superficial carbon on the PCB and the traces are fine.

 

[Hollie]

Well, I didn’t expect this type of reaction. I thought people here shared my passion for repairing things.

It’s not like I know nothing about electronics, and PSUs in particular, this is just the first time I’m trying to repair one myself. Obviously I made some mistakes at the beginning, but sometimes you have to take a risk and turn the thing on. You are never going to be sure you have repaired it until you see it working, and that means there might be more sparks.

Anyhow, I personally like the challenge, and up to some point I don’t might spending extra money if I learn something at the end of the day. The feeling of managing to repair something is priceless.

The PSU is definitely not beyond repair. Despite the “fireworks”, there is only superficial carbon on the PCB and the traces are fine.

Right, I'll say it.

Everyone here has a passion for repairing things. However, there's a limit to the amount of danger most of us are willing to take on. There's a reason why everyone's telling you to stop messing around with mains voltage, it's lethal. The same reason people don't try to repair flybacks. It's not 'a passion' to tell someone that what they're doing could literally kill them.

Anecdotal story: the PSU used in the Q800/Q840AV is notorious for failing and being almost impossible to fix. I tried to get a pile of them fixed by a professional about a year ago and was told that they're all completely done. If you wanted to learn something, convert your machine to an ATX supply and create a soft-power circuit for it so it works the same as it would have done originally. It'll be quieter and more efficient too.