[dip16amp]

The power resistor provides current limiting to the OPA541 except if a short occurs between the output pins and the power resistor input pin. The top solder pads of pins 5 and 7 of the OPA541 and the power resistor solder pads look extremely close to the ground plane. Does it look like it may short to ground around those pins?

 

[Juergen]

Quote:

Originally Posted by dgardner I started with a new PSU PCB and moved all the big caps, precision resistors, rectifier diodes, and connectors from the blown board. Then I put in fresh LM338's and OPA541's and even a new REF02. It worked.

I'm pretty close to trying that. Today I ordered two 541s and a REF02. I already have two spare 338s (and 317s). Unfortunately I don't have a spare board. I'll probably change out all of 338/541/REF02. One bad part about this method is that I would be removing a functional (as far as I know) 541 and to do this I will have to clip the leads rendering it extremely if not utterly unusable. Tis a risky business we're in.

Quote:

Originally Posted by dip16amp The top solder pads of pins 5 and 7 of the OPA541 and the power resistor solder pads look extremely close to the ground plane. Does it look like it may short to ground around those pins?

As far as I can tell it's pretty clean. Currently it isn't shorted but since the 541 is blown that doesn't mean it couldn't have been.

Thanks to all for keeping the little wheels in your heads turning

 

[sft]

Try to get a new ps pcb in US.
some of the first round group-buy pcb are not OK.

Just my 2 cent opinion....

 

[Juergen]

Quote:

Originally Posted by sft Try to get a new ps pcb in US. some of the first round group-buy pcb are not OK. Just my 2 cent opinion....

I have made a few inquiries. Do you know if there is a way to tell if it is a first round board? I seem to remember that the trimmer was not on the earlier boards?

 

[dgardner]

Quote:

Originally Posted by Juergen I have made a few inquiries. Do you know if there is a way to tell if it is a first round board? I seem to remember that the trimmer was not on the earlier boards?

I have one piece of the first round boards. It was the small cap layout. One deoupling cap needs a jumper. There is no trim pot of the REF02. First round boards and second round boards are distinctly different sizes. PM me for complete historical details.

 

[dgardner]

Quote:

Originally Posted by Juergen Unfortunately I don't have a spare board.

I can supply replacement PCBs if necessary. Plenty left from the headwize group buy...

 

[Juergen]

Quote:

Originally Posted by dgardner I can supply replacement PCBs if necessary. Plenty left from the headwize group buy...

With the luck I'm having, I think I might as well start on a new board. I'll PM you with the details.

Thanks

 

[sft]

Quote:

Originally Posted by Juergen I have made a few inquiries. Do you know if there is a way to tell if it is a first round board? I seem to remember that the trimmer was not on the earlier boards?

Your board is the final correct version with big Cap layout.
I'm sure some of this round group-buy pcbs can't pass open and short test.

 

[Juergen]

Starting again...

New board, 3338s, 541s & REF02. Everything else transplanted to new board.

I have had it powered up (with no load) 3 times so far for about 10 minutes each time. Output of +/- 30V steady. Chips are cool. Looks good so far but that was the case the last two times so I'm remaining cautious.

 

[grasshpr]

You can always try using a dummy load to see how well your PSU's endurance is. Make sure you heat sink the load though...

 

[Juergen]

Quote:

Originally Posted by grasshpr You can always try using a dummy load to see how well your PSU's endurance is. Make sure you heat sink the load though...

I ran it or about 45 minutes last night powering the amp boards. The amp heatsinks got really toasty but that is normal. The PSU heatsink got warm. I found a candy/deep fry thermometer and placed it against one of the 541s and got around 100F. It sounded great! I am going out of town for a week so I will probably not try again today. I would hate for it to fail just as I was leaving town. How's that for thinking positive

 

[grasshpr]

Quote:

Originally Posted by Juergen I ran it or about 45 minutes last night powering the amp boards. The amp heatsinks got really toasty but that is normal. The PSU heatsink got warm. I found a candy/deep fry thermometer and placed it against one of the 541s and got around 100F. It sounded great! I am going out of town for a week so I will probably not try again today. I would hate for it to fail just as I was leaving town. How's that for thinking positive

At that temp, I think we could fry bacon. Next build on my list, stovetop amp

 

[steinchen]

after some months of service my Dynahi PSU died too. I switched the amp on to let it warm up and had it on just a few minutes when something inside the case exploded, creating a small cloud rising through the ventilated top panel and blowing the fuse.

First I suspected a tantalum cap had failed short, but when I opened the case I had to realize that the right OPA541 was blown, exactly like Juergen's. The opamp was first mounted on the angled bracket and then soldered down, so I can exclude poor heat dissipation to be the reason. Additionally, the failure happened a few minutes after power up, so it can't be overheating either (I'm using a 30VAC Avel-Lindberg transformer).

For some reason I don't want to solder in a $16 replacement without changing something else and see it pop like the first one.

I noticed significant hum (dependend on the volume pot setting) through my cans shortly before the PSU blew. Therefore I suspect the PSU had locked up during power up or oscillated, maybe due to excessive capacitive load.

Unless anybody can supply a better suggestion (I won't rebuild the whole PSU on another pcb) I'm going to remove the 4700uF caps from the outputs of the opamps before I replace the OPA541. I'm going to repair the PSU next weekend and will keep you informed how it turned out.

 

[Juergen]

Quote:

Originally Posted by steinchen after some months of service my Dynahi PSU died too. I switched the amp on to let it warm up and had it on just a few minutes when something inside the case exploded, creating a small cloud rising through the ventilated top panel and blowing the fuse. First I suspected a tantalum cap had failed short, but when I opened the case I had to realize that the right OPA541 was blown, exactly like Juergen's. The opamp was first mounted on the angled bracket and then soldered down, so I can exclude poor heat dissipation to be the reason. Additionally, the failure happened a few minutes after power up, so it can't be overheating either (I'm using a 30VAC Avel-Lindberg transformer). For some reason I don't want to solder in a $16 replacement without changing something else and see it pop like the first one. I noticed significant hum (dependend on the volume pot setting) through my cans shortly before the PSU blew. Therefore I suspect the PSU had locked up during power up or oscillated, maybe due to excessive capacitive load. Unless anybody can supply a better suggestion (I won't rebuild the whole PSU on another pcb) I'm going to remove the 4700uF caps from the outputs of the opamps before I replace the OPA541. I'm going to repair the PSU next weekend and will keep you informed how it turned out.

Another PSU literally up in smoke

Now you got me worried. After months of working fine I thought mine was safe (knocking on wood). I sure hope you get it working.

 

[flecom]

thats why I used a very simple single linear regulator powersupply for my dynahi... i know that the dynahi powersupply looks real impressive and is regulated to an insane degree... but sometimes the KISS (keep it simple stupid) design method is best

and mine has been on 24/7 for the last year or so