I shorted out the power transformer while recasing my dynahi. Help

[sbelyo]

Ok, so I tested the board in and out of the chassis and the results are the same.  

There's no short from the inputs to the chassis or ground, or to themselves

There's no short from the outputs to the chassis

When I measure resistance on the outputs I get a short (0 ohms) for a solid second on -V to GND but then the meter ranges.  On +V to GND the meter just ranges.

I also measured the voltage on each of the caps and they all read just a few millivolts.

[Mister X]

Quote

the meter ranges.

That's from the the meter charging the caps.

The "short" you saw when you first connected the meter was from one or more of the caps discharging through the meter.

 

And... it's normal practice to power up a device under test before attempting to measure voltage.

Otherwise you're just measuring the residual voltage in the circuit.

 

All of this brings up a question though.

Have any idea how many hours that PSU has been in service?

 

[sbelyo]

I'd say 1500 to 1800 hundred hours over a 9 year period.  I took the amp apart about 6 months ago wanting to re-case it and in the process I got hit by a truck so it took me about 6 months to recover to the point where I could work on it again.  It hasn't had power since October maybe.  Ti suggests switching to a slow blow fuse so I will try that today.

Could it be the caps are just dead from age?

[spritzer]

Yes that could very well be the case. 

[sbelyo]

My next step was to recap it.  I'll try the slow blow fuse or maybe borrow my dad's variac to power it up slowly first.  Then order some caps.

I saw some nice mundorf caps but they're snapin.  Can I just staighten them and dremel the leads to fit the through holes?

[spritzer]

Just stick with proper caps without attempting to add to the clusterfuck.  Just because it has a Mundorf sticker on doesn't mean it is any better than the Japanese stuff and probably inferior. 

[sbelyo]

good point, Nichicon is all that's available it looks like

[sbelyo]

It's running fine now.  I put a 1.6 amp slow blow fuse in it and it fired right up.

I guess it needed that extra few seconds on startup to charge the caps and the current was popping the fuses.  The amp lived it's whole life in the old case with a 1.0 amp fast blow in it.  At least I don't have to build another one

[kevin gilmore]

actually if its that old, your electrolytics are starting to die...  

[sbelyo]

Yeah, I built it way back in the day.  It's seen a ton of use.  Honestly I have no idea how many hours it's been running.  There's been at least three or four times in it's life where it's been left on for days at a time.

I will replace the electrolytics.  I'm guessing the standard grade Nichicon's are ok to use?  That's all that'll fit and meets the specs and is stocked by mouser or digikey