Ah yes, you are likely correct.
I am using a car battery.
I tried looking over the board and jiggling components on the top side while looking at the underside to try to find other bad solder points. I wasn't able to find any.
I didn't need to install a fuse since I have one installed already per your bcae1 instructions
Removed Q332 and Q328 and the LED comes on and stays solid. I would say it looks like it is powered on but wasn't sure what other tests would be ideal at that point.
You'll have to find what's making this channel read differently from the other channels. You may have to check every resistor between the drivers and the outputs as well as look for broken connections between components if the drivers and the output read similarly between channels out of the board.
I printed out a blown up version of the circuit for me to try and follow. Is there a specific technique you would use to do this process?
I was just going to try to go component by component through the schematic and find it on the board starting from B Right channel in the 1C section of page 7.
I am not sure how to test this L854 "ferri-inductor". Looks like it's grey, black, gold, silver but when I tested it as a resistor it didn't match what those colors say. All 4 were the same though (~0.6 ohms) so I figured they are probably all fine and moved on.
I found a couple resistors that didn't match the schematic.
R154 and R153 are surface mount and show 47k in the schematic and 473 on the top but measure 158.6 and 156.9 ohms. That's a head scratcher to me. I thought about maybe taking these ones of circuit to test.
Everything else seemed to measure good until I got to the pre-driver section and I had some weird readings. Before I post about them I'm going to measure the left side of the channel's pre-driver area and compare.
I took out the isolator board and all the resistors match their numbers on them...but they don't all match the schematic. It's actually hard to read some of these numbers from this pdf I have. A clearer, higher quality one might make this a bit easier. I moved on from this and assume it's good since the resistors seem to match their marked values.
We'll see if checking the other half of the channel reveals any secrets to me.
Many more parts to measure.
I found a couple resistors that didn't match the schematic.
R154 and R153 are surface mount and show 47k in the schematic and 473 on the top but measure 158.6 and 156.9 ohms. That's a head scratcher to me. I thought about maybe taking these ones of circuit to test.
Everything else seemed to measure good until I got to the pre-driver section and I had some weird readings. Before I post about them I'm going to measure the left side of the channel's pre-driver area and compare.
I took out the isolator board and all the resistors match their numbers on them...but they don't all match the schematic. It's actually hard to read some of these numbers from this pdf I have. A clearer, higher quality one might make this a bit easier. I moved on from this and assume it's good since the resistors seem to match their marked values.
We'll see if checking the other half of the channel reveals any secrets to me.
Many more parts to measure.
The Lxxx components are inductors (a coil of wire). You're reading resistance with your meter. The markings give the inductance value. You can't measure inductance directly with a standard multimeter.
Set the gain control to the other end of its range and measure the resistors that read too low.
Set the gain control to the other end of its range and measure the resistors that read too low.
That makes sense. I had to read them with my transistor tester and it was what showed me they were ~0.6 ohms each and made me think they were ok since they all measured very close to one another. It didn't say they were inductors but I think it is supposed to be able to read them. The multimeter just registered a small number and flipped around from .1 to .2 to .3 ohms.
I never thought to try the gain control. I went back and checked them and their measurement didn't change. Could it be caused by Q332 and Q328 being out of the board still? Should I put them back in? If not, then maybe the problem is causing these readings. Anyway, my plan is still to measure the sibling area from other half of the channel to compare my results and then move on to finishing the measurements I have left to make it all the way across the schematic. I've made it about 75% across the paper but there are a lot of components left in this last bit.
These resistors in the pre-driver for all channels all measure the same. 7.5k ohms. The schematic shows 15k. The colour bands looks to me like they are brown, green, orange, gold, which seems like it should be 15k ohm (+- 5%) and that would match the schematic. R317, R321, R322, R318, R319, R323, R324 & R320. Is this as weird as it seems and for them all to be that way makes it seem like there isn't an issue. Should I desolder one of them to test it out of circuit?
I don't expect there to be a problem anywhere other than the components between the drivers and the output transistors.
You might try installing the outputs from one of the good channels into the bad channel to see if the problem remains in the bad channel.
Do the same for the driver transistors if the outputs do nothing.
You might try installing the outputs from one of the good channels into the bad channel to see if the problem remains in the bad channel.
Do the same for the driver transistors if the outputs do nothing.
I moved Q330, Q314 and Q326 over to Q332, Q316 and Q328's spots. When I touched the b+ lead to power I heard that little sizzle sound, so I stopped. Any idea what could be making that sound or what components, if any, are capable of that? I checked that all the legs of stuff under the board were shorter than all the plastic standoffs, so I don't think it's arcing to the heatsink.
I thought about taking Q330, Q314 and Q326 back out of the broken channel and putting the ones from the broken channel (Q332, Q316 and Q328) into Q330, Q314 and Q326's spot to confirm that channel works with them in there, if you think that's worth it.
What ones precisely do you mean by "driver transistors"? Sorry, I don't know for sure which those are and I don't want to guess wrong. My guess would be Q316 and Q314 and since I swapped those as well as took them out and put them in the transistor tester and they measured similarly as NPNs, I am thinking they are fine.
If resistors don't sizzle, I was thinking is that more likely to be a capacitor or one of these other Q numbered components? At this point I was just trying to decide which components to desolder and test out of circuit first.
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No, it did not blow the fuse. The crackling just kind of scares me since it doesn't do that when that messed up channel had no output transistors in it. I certainly didn't want to break any more components. The power LED was back to flashing also.
Ok. I pulled out some of the driver transistors back on the 12th. I pulled Q312 & Q310 (they say C2705 on them) and Q308 & Q306 which are 2SA1145 in the book and show A1145 on them. Are only the C2705s driver transistors or the A1134s are also?