I recently completed my Ambika. I did not notice, but what I thought was a LM2940-8.0 was intact a LM2940-12. I was not paying attention to y voltage check and must have missed the board having +12V instead of +8VDC.
Anyway, it did not seem to bother my SMR-4 board. it seemed to play ok and this extra high voltage did not kill it.
More recently I built a Tube Ohm Ladder board for my Ambika and powered it up before noticing that the LM2940-12 was wrong. It played for a little while and then it seemed to die.
I checked for the various voltages, and thats when I noticed the LM2940-12. so I swapped it out with a LM2940-8.0.
So now the Ladder board has about 3.9V on MP1 instead of 0.38V or so. I swapped out the ICs so they are all good, but still, I only get a really faint sound. What parts should I start checking? Is it possible I blew the transistors in the filter? (based on the really high voltage at the bottom of the ladder this is my guess)
Any ideas would be welcome.
I just swapped out all the ICs because they were socketed, no differences. But I did not swap out the transistors because they are soldered in… I think I am going to have to try and swap those out.
I did a similar wrong thing on my Ambika before. I accidentally plugged a12V DC psu in It and it broke nearly all SMR-4s mounted on it. The experience of it is to replace every ICs on boards include all transistors(4x 2n3906). Because they are the most fragile parts under wrong voltages. Or you can check all data sheets for voltage limitation for all of them to rule out trouble makers. I don’t have a Tube Ohm Ladder board to figure out which part could be broken, so I couldn’t help you more. Or maybe an image of it would help.
Yes, you should. Some of my SMR-4 boards got cranky noises after that accident, then I fixed them by swapped all transistors.
Hi , there is something wrong on your Ladder board. Normally you canb’t damadge something with 12 Volt .
Take a look to the schematics. The testpoint 1 had only 2 resistors . This resistors are a voltage divider and generate the 0.357 volt. There must be the mistake .
thanks. I will check the resistors.
I had a wrong resistor in R21. I replaced it with a 220 ohm resistor and it sounds fine now.
Thank goodness, no blown transistors. Just one wrong resistor.
With the 220 Ohm R21 I got close to 0.357V at the first test point.
The board sounds great!