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TM3030 PSU trimming problem
MUFF WIGGLER Forum Index -> Oakley Sound Systems  
Author TM3030 PSU trimming problem
erroland
Hi.
I have just completed a TM3030, my first project. I'm at the trimming and tuning stage but when trying to trim the voltage to 5.333 I can't get it lower than 8.4. Does anyone have any ideas?
Cheers
Errol.

P.S. If you happen to read this Tony after receiving the board back it responded to midi straight away, not sure what the issue was there, maybe my computer, its a bit moody sometimes. The output issue was a bad connection at the audio out, so, nearly there just this trimmg issue now.
Synthbuilder
Errol,

I am hoping it is not really reading 8.4V or we have a problem. Are you sure you are measuring the right points? Try looking at the voltage between points pin1 of U13 (+5.33V) and pin 4 of U13 (ground). It's easier than using the ground pin of the midi socket.

If this can't made to get to exactly 5.33V then have a look at the voltage on the output of the LM723. This is the voltage between pins 3 and 7 of U10. What are you getting there? It should be around 15V.

Tony
erroland
Hi tony.
Yeah i checked using pin 1 and 4 of U13 and still 8.4 is the lowest it seems to go and the voltage between pins 3 and 7 of U10 is 26.4! Sounds bad.
Errol
Synthbuilder
erroland wrote:
... the voltage between pins 3 and 7 of U10 is 26.4! Sounds bad.


OK, you have a major fault with the first power supply section. ie. the bits around U10. Don't switch it on again until you have checked around U10 for shorts to the casing or misplaced wires.

Now remove U10 completely. Switch it on again and measure again the voltage across pins 3 and 7 of the now empty IC socket. What do you get?

If it's 26V again you have a short somewhere that is allowing in the raw unsmoothed DC voltage either from your power pack directly, or via some board short around U10.

If it's 0V then replace U10 with a fresh LM723.

What power pack are you using? DC or AC?

Tony
erroland
Hi Tony.
I removed U10 and measured the voltage of the empty IC socket between 3 and 7 which was 0V, so i'll replace the LM723 and hopefully things will be ok. The power pack i'm using says AC/DC and its 24v. I'll let you know how things progress.
Thanks for your time.
errol.
erroland
Hi Tony.
Update on this problem- I have just gotten around to replacing the LM723 but am still getting the same reading. I'm at a dead end again, anything else i can try or will i have to send it back to you again?
thanks.
Errol
Synthbuilder
erroland wrote:
... will i have to send it back to you again?


I'm thinking that you may have to. If you do, can you send the whole lot back and not just the board?

Tony
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