[dip16amp]

Quote:

Originally Posted by kin0kin checked, they are 0.2ohm, no voltage drop across them. My toroidal are 18V as opposed to 22V AC seen in the picture. What should I do next? is there a way to check if the LM338 and OPA541 are working properly?

That transformer seems to have too high of an output for an 18 VAC. The noload output should not be more than 22 VAC. The peak value 22*1.414=31 and with diode voltage drop, should be about 25 vdc instead of 35.8 vdc. You could measure the voltage drops across each of the rectifiers.

 

[kin0kin]

hmmm all the rectifiers measure about 17.8-18V. I've also tried loading the psu with a 12V DC fan (current rating unknown), the output measured 21V as oppose to 23V. how can I solve this? I know I can regulate the output with a LM138 on each rail (5A) and bring them down to 16V but this shouldnt be needed at the first place.

 

[kin0kin]

here's another thing. I tried changing the gain resistor of the opa541, which is suppose to set the psu's output...but it doesn't do anything....it still remains at 23Vout....

 

[dip16amp]

With power off, try checking continuity with an ohm meter from the output to the 22.6k ohm resistor, then pin 2 of the OPA541 to the 22.6k and 10k ohm resistors. Also try measuring the resistors on the board. May have to measure for a minute or two while the cap changes the readings.
Also make sure the 10k resistors are labeled 1002F and the 22.6k is 2262F.

 

[kin0kin]

the resistors are definitely right, I have removed them and measured them seperately earlier. one thing is that....am I suppose to get +/- 16V ONLY when they are powering the dynalo? the Vout I've taken are unloaded Vout from the psu alone.

I can think of two solutions if this doesn't go right:
1) bypass the 541's stage and set the 338 to 16V
2) regulate the output of the opa541.

I hope i dun need to do this though.

 

[bg4533]

Are you positive that all of the tabs are isolated from each other? The OPA541s can be connected. Everything else should be separate.

I have a Dynahi PSU powering a Dynalo, but i think my resistor values are a bit different so my readings aren't completely relevant.

With PSU on and no load:
Transformer =21.37VAC per secondary
Tab of OPA541=25.3VDC
Output voltage set to 16.3V
I can adjust over a volt in each direction (maybe more but I didn't try)

Measuring things on my PSU is difficult with my setup, but if you need more let me know.

Under load my PSU gets a bit warm. I have everything mounted to piece of angle iron and an old computer heatsink mounted to that.

Also, I can't think clearly enough to know if it matters or not, but your trim pot is backward.

 

[bg4533]

Quote:

Originally Posted by kin0kin the resistors are definitely right, I have removed them and measured them seperately earlier. one thing is that....am I suppose to get +/- 16V ONLY when they are powering the dynalo? the Vout I've taken are unloaded Vout from the psu alone. I can think of two solutions if this doesn't go right: 1) bypass the 541's stage and set the 338 to 16V 2) regulate the output of the opa541. I hope i dun need to do this though.

The PSU output variation should be minimal whether unloaded or loaded.

Don't give up yet, you should be able to get it going.

 

[kin0kin]

yes they are seperated, in fact the heatsink is not mounted now.
the opa541's tabs measure close to yours - 26V. the main problem is, adjusting the gain doesn't do anything to the output. Adjusting the pot does change the ref voltage and is suppose to change the output voltage since it is amplified by the 541s. I do believe that the Vout should be 16V regardless of the load. I'm trying to avoid coming to a conclusion where the 541s are faulty. And if that is the case, I'm just gonna remove them and let the 338s do the regulation and setting. I really dun feel like forking 30+ bucks out for the 541s.

I'm very close to powering the dynalo with 23V now....but I was told by Dan that I wouldnt wanna go beyond 16V. all the parts in the dynalo that are voltage dependent are rated >25V, they should be fine even if I feed them with 23V.....but I'm not sure if feeding 23V would do something odd to the trannies. Should I give it a try and fire it up? who knows maybe my DMM aint reading the Vout properly for some reasons. What'd be my worse case scenario if I fire the dynalo up with 23V anyway?

 

[Pars]

Quote:

Originally Posted by kin0kin yes they are seperated, in fact the heatsink is not mounted now. the opa541's tabs measure close to yours - 26V. the main problem is, adjusting the gain doesn't do anything to the output. Adjusting the pot does change the ref voltage and is suppose to change the output voltage since it is amplified by the 541s. I do believe that the Vout should be 16V regardless of the load. I'm trying to avoid coming to a conclusion where the 541s are faulty. And if that is the case, I'm just gonna remove them and let the 338s do the regulation and setting. I really dun feel like forking 30+ bucks out for the 541s.

I would try not to do this as one of the huge benefits of the Gilmore supplies are the output opamps. The entire PSU up to the 541s is there pretty much just to power them. You would be removing the last and very important stage of regulation, plus giving up the tracking.

Quote:

Originally Posted by kin0kin I'm very close to powering the dynalo with 23V now....but I was told by Dan that I wouldnt wanna go beyond 16V. all the parts in the dynalo that are voltage dependent are rated >25V, they should be fine even if I feed them with 23V.....but I'm not sure if feeding 23V would do something odd to the trannies. Should I give it a try and fire it up? who knows maybe my DMM aint reading the Vout properly for some reasons. What'd be my worse case scenario if I fire the dynalo up with 23V anyway?

I'm not sure what would happen with that high of voltage. Your DMM is certainly working to the extent that you should see movement on the Vout when adjusting the pot, even if it is off on its voltage measurements. I would have to think that your problem lies in the 541s... solder joint, bad/no connection to a pin, etc. Keep at it... maybe swap the 541s around (I know they are a pita to desolder) if you can't find anything else. I'm not sure if 548s are pin compatible or not (they probably aren't but check the datasheets), but those you can get off of ebay for relatively cheap ($25 for 5 of them or something like that).

 

[dip16amp]

The voltage across the 22.6k ohm resistor should be 11.3 volts and 5 volts across the 10k ohm resistor when the output should be 16.3 volts. If the output is 23 volts, then 7 volts will across the 10k and 16 volts will be across the 22.6k. The 7 volts across the 10k should also be on pin 2 of the OPA541. If 5 volts from the ref chip is on pin 1 of the OPA541, the difference between pin 1 and 2 should drive the output down until the voltage across the 10k drops down to 5 volts. Once both pins are at 5 volts, the output should be 16.3 volts.

 

[rellik]

i dont know if this is any help

i remember someone previously was having issues wih their dynahi psu board becuase their tantalum caps were not oriented correctly since they are polarized

im clueless otherwise, sorry

 

[kin0kin]

hey guys, thanks for all the input so far. I really wanna fire this sucker up. I'm taking a break from this problem for awhile I dun wanna snapped the board apart which I really am close to doing so

I'll do more checks on the board in awhile.

btw, the tants are oriented properly

 

[dip16amp]

If you are sure the voltages are getting to the actual pins of the OPA541, then pull the first OPA541 off. The second OPA output should then drop to zero volts as it trys to track the zero volts of the first OPA output. Hopefully, both of them should not be bad.

OPA541 pinout

2 4 6 8 10
1 3 5 7 9 11

pin vdc
1 5v
2 5v
3 -26v
4 -26v
5 16.3v
6 nc
7 16.3v
8 16.3v
9 nc
10 26v
11 26v

 

[MisterX]

Quote:

Originally Posted by rellik i dont know if this is any help i remember someone previously was having issues wih their dynahi psu board becuase their tantalum caps were not oriented correctly since they are polarized im clueless otherwise, sorry

Here is the link to that thread---->
http://www6.head-fi.org/forums/showthread.php?t=118176

But I dunno if it will help or not.