Presonus Digimax External PSU Problem

Hi,

I have used this unit for severals years, this is the older unit with external PSU.

Of time to time the +16 Volts was presenting an erratic behavior from +16Volts to 0Volts and I changed the LM317 voltage regulator and the PSU was working well for few seconds and again show the same behavior to 0volts in the +16volts.

I analyzed the schematic (btw: that is very simple network at all!) and before I figure nothing rare in others components inside of this simple PSU, I checked  the input voltage and found -50Volts and +50Volts in both LM IC 317, 337 respectively....This look like very high voltage to me because the data sheet say "Input−Output Voltage Differential" Max 40Volts.......and 50Volts minus 16 Volts (50 - 16 = 34) are 34Volts that is to near to the limit! this can be causing my -16Volts LM317 regulator go bad every time I change it?...

I want to be noted the very high temperature of this units is common in this PSU from I purchased and this the same in anothers units of the same model with external PSU; look like this PSU is in the limit, not for the unit itself but the LM IC voltage regulators are in the power and input voltage limit!! .

I am thinking to interchange the LM317 and LM337 pair for another IC regulators with more power management like the LT1085 and LT1033 in place for the +/-16Volts.

My question is: Someone have had this same problems before with this IC LM317??......Is my situation a typical behavior of this "near limit situation" for the LM IC voltage regulators?

Thanks
Opacheco

I think that the AC LINE input for the power supply should be 120 volts, not 230 volts.

The power supply for the regulators should have been designed for 24 volts input not 50 volts.
During turn ON the DC voltage is ZERO and then the capacitors charge to 16 volts, this applies 50 volts across the voltage regulators and they will FAIL.

If your AC Line is 230 volt get a step down transformer to get 115 volts.
Duke

Not sure which Digimax model you have.  I have three of the Digimax FS boxes, which use an external switching power brick.  DC in is rated for something like 12 to 24VDC, and I think also allows AC.  I haven't looked at the inside PSU schematics though.

Either way, if yours is anything like mine, 50V is waaaay too much.  I would suspect something is wrong with your external (AC-to-DC) PSU.  Try a different power brick.

Audio1Man said:

I think that the AC LINE input for the power supply should be 120 volts, not 230 volts.

The power supply for the regulators should have been designed for 24 volts input not 50 volts.
During turn ON the DC voltage is ZERO and then the capacitors charge to 16 volts, this applies 50 volts across the voltage regulators and they will FAIL.

If your AC Line is 230 volt get a step down transformer to get 115 volts.
Duke

Click to expand...

Duke,

I am using the AC 120v and I don't know why the 50V appear in this PSU???......I will check the power transformer connections for any  wire error!
Thanks
Opacheco

SirNickity said:

Not sure which Digimax model you have.  I have three of the Digimax FS boxes, which use an external switching power brick.  DC in is rated for something like 12 to 24VDC, and I think also allows AC.  I haven't looked at the inside PSU schematics though.

Either way, if yours is anything like mine, 50V is waaaay too much.  I would suspect something is wrong with your external (AC-to-DC) PSU.  Try a different power brick.

Click to expand...

Dear SirNickity

My Digimax is the older unit, sample rate are 32K, 44.1K and 48K and the PSU is ANALOG power supply instance to SWITCHING power supply. I suspect of the secondary transformer voltage or wiring......I will check it again because I can't see any trouble in the electronic (simple electronics) before the IC's LM317 and LM337 at all.

Thanks a lot
Opacheco

I had checked all wiring and the AC voltage in the secondary toroidal transformer and found everything is ok;

18.4Vac - 0Vac - 18.4Vac

But when I Connect the Board (Rectifier, Filtering and regulation LM317 and LM337) this voltage goes up to 50Volts DC only for the LM317....But the LM337 is ok with -16.3 Volts DC. I don't know why the +16 Volts DC is very high???...

I am planning to exchange these LM317 and LM337 to LT1085 and LM1033 for more Currents amperes.

Any comment?

Opacheco.

It sounds like either the +DC rail is referencing the -DC rail rather than a center tap at 0V -- 18vAC * 1.414 * 2 is about 50V -- or the rectification diodes are acting as a voltage doubler.

Do you have continuity between the CT and the reference pins of both linear regs?  Have you measured from the CT to see if you're getting 18vAC on either end of the secondary winding?

I don't think swapping the regulator IC is going to solve your problem.  It's not going to boost the voltage to 50V because it's overloaded.

SirNickity said:

It sounds like either the +DC rail is referencing the -DC rail rather than a center tap at 0V -- 18vAC * 1.414 * 2 is about 50V -- or the rectification diodes are acting as a voltage doubler......

Click to expand...

YES!!....I checked the secondary winding conector of toroidal transformer and found the CT and one Leg was incorrectly exchanged in the manufacturing ensamble !!  See the attached pic; The red wire is the CT and must be in the pin 3!!......because that the 50Volts DC in the positive input of LM317!! (see my pics)......

I tested the voltages and found +24Volsts DC in the +16Volts DC pin and this show the LM317 was burned for the bad connection!!.....The other Voltages are ok!!

I will change the LM317 and let you know!

Thanks a lot for your advises
Opacheco.

opacheco said:

YES!!....I checked the secondary winding conector of toroidal transformer and found the CT and one Leg was incorrectly exchanged in the manufacturing ensamble !!  See the attached pic; The red wire is the CT and must be in the pin 3!!......because that the 50Volts DC in the positive input of LM317!! (see my pics)......

I tested the voltages and found +24Volsts DC in the +16Volts DC pin and this show the LM317 was burned for the bad connection!!.....The other Voltages are ok!!

I will change the LM317 and let you know!

Thanks a lot for your advises
Opacheco.

Click to expand...

Look like the C1 is being charged to 50Volts DC in each cycle of the wave, this is the reason of this high or double DC voltage in the input of LM317....

Opacheco.

Glad you found the problem!    Hope that regulator IC took the brunt of it and saved everything downstream.

SirNickity said:

Glad you found the problem!    Hope that regulator IC took the brunt of it and saved everything downstream.

Click to expand...

SirNickity
Me too!!.....and I will try to install the LT1033 and LT1085 instance to LM3317 and LM317 in order to get a better performance for current supply and a better temperature performance in these parts because they run very, very hot!.....

Thanks a lot for you advice
Opacheco.