kent
Well-known member
Hi All
I have recently put together my MNATS 1176 rev A with transformers and transistors from Hairball. It looks good but I am blowing fuses and it has me stumped. Here's the symptoms:
The first time I fired it up and started calibrating everything was going fine. Set the Q bias and started setting the meter when I got interrupted and had to turn it off and finish later. The next time I tried to turn it on it popped a fuse. I tried it again a couple more times and blew those fuses as well. Went out and bought more fuses, blew a couple of those and then the next time it stayed on so I checked my voltages both off of the power supply and directly off the power transformer. Those measurements all looked fen once again. Then I blew a few more fuses. Even with disconnecting the transformer from the board and having no load at all it blew a fuse. I removed the power switch so just plugging it in would power it up wondering if the switch was bad and shorting internally . Another blown fuse. After resoldering and double checking all my connections again which appeared ok I turned it on and it stayed on. However I noticed this time when I sent a test tone to start the calibration process again the meter slowly but surely started reading lower and lower level until after an hour or so it settled at some arbitrary level. At least now it would turn on and off without blowing fuses. So I checked the power supply again and everything looked fine. I started doing the calibration and I could get no meter deflection while adjusting the Q bias. When looking at the voltage directly off the Q bias wiper with my meter it was reading a nicely varied couple of volts range. So this morning I was going to go back at it and trouble shoot some more but - it started blowing fuses again.
So after that long winded post - does anyone have ideas on where to start checking next? Is it possible that the power transformer is suspect? That seems unlikely to me. Thanks.
I have recently put together my MNATS 1176 rev A with transformers and transistors from Hairball. It looks good but I am blowing fuses and it has me stumped. Here's the symptoms:
The first time I fired it up and started calibrating everything was going fine. Set the Q bias and started setting the meter when I got interrupted and had to turn it off and finish later. The next time I tried to turn it on it popped a fuse. I tried it again a couple more times and blew those fuses as well. Went out and bought more fuses, blew a couple of those and then the next time it stayed on so I checked my voltages both off of the power supply and directly off the power transformer. Those measurements all looked fen once again. Then I blew a few more fuses. Even with disconnecting the transformer from the board and having no load at all it blew a fuse. I removed the power switch so just plugging it in would power it up wondering if the switch was bad and shorting internally . Another blown fuse. After resoldering and double checking all my connections again which appeared ok I turned it on and it stayed on. However I noticed this time when I sent a test tone to start the calibration process again the meter slowly but surely started reading lower and lower level until after an hour or so it settled at some arbitrary level. At least now it would turn on and off without blowing fuses. So I checked the power supply again and everything looked fine. I started doing the calibration and I could get no meter deflection while adjusting the Q bias. When looking at the voltage directly off the Q bias wiper with my meter it was reading a nicely varied couple of volts range. So this morning I was going to go back at it and trouble shoot some more but - it started blowing fuses again.
So after that long winded post - does anyone have ideas on where to start checking next? Is it possible that the power transformer is suspect? That seems unlikely to me. Thanks.