Negative voltages on Sproggy 2.8 way off, need help.

**rbarr110** · 09-06-2002, 12:09 AM

My -12V is giving me a -32V reading and my -5V is reading as -0.36V. All other voltages are ok.

Component placement all appears correct and I have double checked to make sure no traces are connected.

Anyone have any ideas?

**THEMP3KID** · 09-06-2002, 03:06 AM

Well......... the -12volt does fluctuate due to the load on the +12volt.. The min (max) input voltage of the -5volt regulator is -20volts, therefore feeding it with -32 killed it.... umm.... possibly you have the rectifying diodes for the +12 and -12volts in teh wrong place...... you may be using both secondary windings for the -12volt accidently........ well... thats all I can think of without looking at it..

**Robbedoes** · 09-06-2002, 03:11 PM

buy a MAX765 and take -12v from the 5v line, like the sproggy 2.0
works for me

**rbarr110** · 09-16-2002, 02:03 PM

I have contacted Mastero regarding my problem and he suggested that I replace the 79L05.

I wasn't able to find a 79L05 locally but another part that is a -5V negative voltage regulator 1Amp part. The 79L05 is a 100mA part. So I thought what the hell, and tried the other part. The new part got extremely hot and started smoking, so I figured I need to try and find a 79L05 voltage regulator.

So I removed the new part and decided to test the voltages to see if the voltages were any different from when the 79L05 was in place. The voltages read -32V at the -12V, and -0.35V at the -5V location.

Therefore the 79L05 was bad, and/or somewhere else something is bad and is feeding way too much voltage for my negative lines.

I am currently in the process of locating a new 79L05 locally but am gladly taking more suggestions.

Thank goodness the forum is back up.

**mp3hombre** · 09-16-2002, 09:13 PM

Could you post a picture of your power supply?

**THEMP3KID** · 09-16-2002, 09:23 PM

Originally posted by rbarr110

Therefore the 79L05 was bad, and/or somewhere else something is bad and is feeding way too much voltage for my negative lines.

I am currently in the process of locating a new 79L05 locally but am gladly taking more suggestions.

Thank goodness the forum is back up.

The part was bad because your powersupply killed it by exceeding the the maximum input voltage... replacing it will just result in the same thing.. the problem is your -12volts, get that working, then put the -5volt regulator in....

**rbarr110** · 09-16-2002, 11:20 PM

I will try to get a digital camera tommorrow so I can post a few pictures and hopefully figure out my problem.

Does anyone have guesses as to why my -12V is so freaking high (-32V)?

Could my 47uH inductors be affecting the -12V, I didn't get 5 Amp parts that other people have used but 10 Amp parts (I think all my coils are 10 Amp parts). My 47uH coils don't have the plastic shield around them but are definately 47uH.

AS far as I can tell everything is in the correct place.
Does anyone have any pictures of a working 2.8 sproggy that I can compare mine too?

Thanks