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Post by kilroyrock on Jul 18, 2016 6:00:31 GMT -6
I got this pre for 15 bucks from craigslist, knowing that there is a fuse blowing upon turning it on. I got a cache of fuses and tried it out. Lo and behold, it blows in about 3 seconds.
I opened it up, surprised to see no surfacemount parts, so it's completely workable, which looks like fun.
I'm wondering if there are places you would immediately look within the power supply that typically would overload and blow the fuse? I don't know much about power supply circuits, I figure this would be a good way to learn what can go wrong. I'll post separately from my phone where I have some pictures. Would you look at resistors? Capacitors? Diodes?
There are some spots that look questionable to me. I think a few resistors and a capacitor that looks like it could use a little better of a soldering job. I would think though that in that case that it just wouldn't even turn on? I get lights on the front for that few seconds, so it's something.
Thanks for any help! |
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Post by kilroyrock on Jul 18, 2016 6:02:46 GMT -6
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Post by svart on Jul 18, 2016 6:29:18 GMT -6
By the solder on the diodes, and the tape on the wires, it looks like someone has already tried to troubleshoot it.
Pull the secondary transformer wires from the PCB, then power it on. If the fuse still blows, then your transformer is shorted.
IF not, test the diodes, then look for any series components after the rectifier diodes and pull those and test the fuse again.
If not, measure voltages after any regulators.
try to work in sections, like measuring analog supply voltages, then measure digital supply voltages. Follow the problem.
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Post by kilroyrock on Jul 18, 2016 7:03:15 GMT -6
thanks svartWhat would a secondary transformer wire look like? Is that the power that goes to the pcb? To make sure I understand what you want me to do and why: So you want me to pull the wires from the board, turn it on and see if I still get a blown fuse. That means it's nothing to do with the board but the transformer is bad. If not, then I reattach the wires removed, and move to diodes, then regulators. Do I do this with it turned on, or will my digital multimeter be able to test the regulators? I know I can test parts, but not sure about circuits without power? |
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Post by rocinante on Jul 21, 2016 8:26:33 GMT -6
The secondaries are the wires that go to the board whilst the primaries go to your iec. The transformer is converting 110v (your mains voltage) into 15v or 12v. So the wires that look like they connect to the fuse Do NOT disconnect. The wires that connect to the circuit are the ones you want to disconnect.
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Post by kilroyrock on Jul 21, 2016 12:55:25 GMT -6
The secondaries are the wires that go to the board whilst the primaries go to your iec. The transformer is converting 110v (your mains voltage) into 15v or 12v. So the wires that look like they connect to the fuse Do NOT disconnect. The wires that connect to the circuit are the ones you want to disconnect. Thanks! should I worry about these two flailing 12v wires I just disconnected? Just keep them apart and turn it on, or should I connect them to each other, or my MM? |
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Post by rocinante on Jul 21, 2016 12:57:14 GMT -6
Keep them apart. Keep them apart. oh please keep them apart.
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Post by kilroyrock on Jul 25, 2016 6:23:42 GMT -6
So I got 20 minutes to play with the testing, and I can confirm that the transformer itself does NOT blow the fuse! So if all else fails, I have a $15 toroidal transformer for another diy kit! Now for the rest of the testing..
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