Tweet
Sounds like something that would be obvious to you guys so i figured i'd see what u think. Same as lat post, a powered monitor but this is the other one in the pair which just started doing this. I turn it on and i get a low hum that sounds like a PSU cap gone bad. But every second or so i hear a click like a relay kicking in but there is not relay. Each time it clicks the hum changes in volume. So every second it clicks and goes from the hum to a lower volume hum maybe 25% quieter then back again. If i freeze various parts it will at times change to where it clicks much faster, maybe 2-3 times a second and still changing the hum volume with each click.
-
-
What monitor is this?
"Same as lat post, a powered monitor?"
It sounds like the PSU is trying to start but then goes into protect.
Edit: this one maybe: http://music-electronics-forum.com/a...g2-scheme-.pdf -
Yeah, thats it. These things are just weird. I checked every component on the other one and somehow it started working but would eventually go back to it's issue till i froze the board/components and i found a area that seemed to affect it. I came to the conclusion it was the board not a component because it would affect it when i sprayed it in various places around the certain area. So i hit some joints while it was playing and the volume would fluctuate and stay low or high. Till i finally seemed to hit the right solder and it stayed normal after that. This one has a different issue but i'm beginning to thing it too is some sort oe board/solder issue. These things are truly crap.Originally posted by Jazz P Bass View PostComment
-
Well, i found something that isn't right but i'm not sure what could be causing it. The smaller of the 2 power supplies, the one on the bottom of the schematic above isn't working right. I tested the output and the + side is 24 VDC while the - side is 15 VDC. Problem is, i swapped the 2 caps and tested the 2k resistors and D101-104 all of which check out fine. Can something downstream from the supply cause that? If not, is it likely the transformer?Comment
-
Do you have + & - 15V from the other supply, the upper one?Originally posted by Enzo
Comment
-
Thats screwy too, 10 and 18VDC. Is there any way it could NOT be the tranny? It's hard to see much on the schematic but the PSU i was able to figure out. After that tho it's hard if not impossible to determine whats what. Coming out of the tranny i get 18VAC on one side and 16 on the other.
EDIT: Ok, i was using the wrong ground. Using the middle pin of the PT connector i get about 20 VDC and 14 VDC on the lower and top supplies respectively, but now each supply's + and - are equal. But i don't even know what they should be.....maybe they are both supposed to be 15 VDC? Thats what i'm assuming and the lower one is therefore 5 VDC over maybe. I juts wish i could read that friggin schematic !
Also, i noticed the tranny has a voltage pinout and it reads correctly, or at least close. (1 VAC higher on both sides)Last edited by daz; 05-05-2015, 04:58 PM.Comment
-
From what I can make out, the upper power supply (a Pass supply) is the + & - 15Vdc supply for the preamp opamps.
The 15 volt zeners hold the base of the transistors at 15 volts & therefore the transistors should 'pass' 15 volts.
The lower supply is the high voltage supply for the output stage.
I see 35V capacitors, so I would expect a higher voltage than 20V's.
Unless there is a connector that can be pulled from the PSU, you may have to lift the TDA2052 ic's to see if that supply comes up.Comment
-
I did not expect that you would reinstall the TDA Ic's.
I would want to know why the power rail is at 20 volts.
My thinking was to eliminate the TDA load.
If that did not bring up the voltage, keep looking.Comment
-
By the way, what is the Vac ripple on the low power rail?Comment
-
-
Volt Meter.
Set it to read Volts AC.
I have seen high enough ripple that a 30 volt supply 'looks like' 20 volts.
It means the caps are bad.Comment
-
Problem is, i've swapped out most all the eletros (all the PSU ones and any other that is suspect for it's position) in this and the other one yet. Even swapped out a few dics that on the schematic looked like they could be suspect due to thier position in the circuit. But i'll check for AC anyways.Originally posted by Jazz P Bass View PostComment
-
DAz, my rule is never look for reasons not to check something. You may have swapped out the caps, but that doesn't mean there is not some cracked trace on the circuit board that effectively leaves the cap out of the circuit, for example.Education is what you're left with after you have forgotten what you have learned.Comment
-
I know, but one of the first things i always do is check all solder joints and cables etc because those are by far the most common problems. I also hit a lot of even slightly suspect joints. Plus anything i can check w/o pulling them i do. Then once that runs out i start pulling parts in the most suspect positions, but on this thing thats tough due to the illegible schematic.Originally posted by Enzo View PostComment
Comment