HELP! Rescuing Dad's old PL400 S2 (pics)
- Thread starter lightfall
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in diode mode at 200ohm settings on the first GE output I get 0.544 one way and it just shows "1" the other way, which I am guessing actually means nothing on this multimeter which doesn't have a manual with it.
I did the following, and the pattern appears to hold true for this unit. I am supposing this means this output transistor is actually doing the intended one way operation. "Lets say you have found that you have a NPN transistor, and have identified the base, emitter, and collector. Set your meter for diode test, and place the positive lead on the base. Place the negative lead on the emitter. You should read a diode drop voltage of about 0.45 to 0.65V. Now place the negative lead on the collector. You again should read a diode drop of about 0.45 to 0.65V (these values are not written in stone...the 0.45 to 0.65V is the most common range however). Now place the negative lead on the base, and the positive on the emitter (called 'reverse biasing'). There should be no conduction. Now move the positive to the collector, and again, there should be no conduction. Lastly, move the negative to the emitter. Again, there should be nothing."
I did the following, and the pattern appears to hold true for this unit. I am supposing this means this output transistor is actually doing the intended one way operation. "Lets say you have found that you have a NPN transistor, and have identified the base, emitter, and collector. Set your meter for diode test, and place the positive lead on the base. Place the negative lead on the emitter. You should read a diode drop voltage of about 0.45 to 0.65V. Now place the negative lead on the collector. You again should read a diode drop of about 0.45 to 0.65V (these values are not written in stone...the 0.45 to 0.65V is the most common range however). Now place the negative lead on the base, and the positive on the emitter (called 'reverse biasing'). There should be no conduction. Now move the positive to the collector, and again, there should be no conduction. Lastly, move the negative to the emitter. Again, there should be nothing."
Ha! Sorry, I am so wrapped up in this. I am Brad. I live in Milwaukee and I don't know a soul who could have possibly helped me with this locally so I have to say I am really appreciative of you putting up with me learning this troubleshooting process. It is actually pretty darn fun, can't wait until it is up and running and I can appreciate the fruits of labor and show it off.
Yourself?
Yourself?
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Yes, I get .544, which seems to be in spec according to the transistor diode guide.
+ on base and - on emitter or collector I get .544, in reverse I get nothing with the - base and + emitter or collector shell.
I am going to repeat this process for all of the outputs tomorrow and write down any ones that don't behave in this pattern. That will identify which of these outputs is bad and then I will see if there is other troubleshooting and what/why that would be before I reinstall them or do anything else.
But man I am tired, will update tomorrow after some serious caffeine, ha. Wyoming is next on my list of backpacking trips; you folks have the tetons AND yellowstone, a treasure trove of geography!
+ on base and - on emitter or collector I get .544, in reverse I get nothing with the - base and + emitter or collector shell.
I am going to repeat this process for all of the outputs tomorrow and write down any ones that don't behave in this pattern. That will identify which of these outputs is bad and then I will see if there is other troubleshooting and what/why that would be before I reinstall them or do anything else.
But man I am tired, will update tomorrow after some serious caffeine, ha. Wyoming is next on my list of backpacking trips; you folks have the tetons AND yellowstone, a treasure trove of geography!
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I also test transistors with the diode test function. Its not absolutely fool proof but it will identify shorts and opens very quickly. Half a volt is about right. If you get one that shows 0.001 or so, its shorted. If you just get a "1", its open. Most of the time when an output device fails, it will do one of those two things. Shorts are what make fuses go, opens just produce weak or distorted sound.
I might suggest testing the drivers too, just in case. THey probably are OK but you may as well know for sure. I did pop one on my friend's 700, but that was my screwup. His were mismatched though, so something had happened in a previous life. All of his output transistors were original though, so I really can't explain it.
I might suggest testing the drivers too, just in case. THey probably are OK but you may as well know for sure. I did pop one on my friend's 700, but that was my screwup. His were mismatched though, so something had happened in a previous life. All of his output transistors were original though, so I really can't explain it.
For a moment I did not realize that the drivers, AKA the bottom row of transistors on the back, were not also just outputs. They have the smaller emitter resistors that I was testing. I will also test the driver transistors.
Now, these have a particular orientation I imagine. Is there a good way to keep track of that since they appear otherwise unmarked? I figure if I put on in backwards it would screw things up. I am also stupid because the first one I pulled I didn't mark the orientation, and if I had not taken pictures ahead of time I would not have realized the orientation after the fact!
Now, these have a particular orientation I imagine. Is there a good way to keep track of that since they appear otherwise unmarked? I figure if I put on in backwards it would screw things up. I am also stupid because the first one I pulled I didn't mark the orientation, and if I had not taken pictures ahead of time I would not have realized the orientation after the fact!
I think I found my first bad one, and a questionable driver.
In the last column the 2nd one shows 0.48, the 3rd one down shows a beep and a .003 +B -E/C and vice versa. The driver in that column shows .51 +B/-E and .46 +B/-C. Does that difference between the E and C reading mean anything? Does it matter that the second one shows .48 whereas the first one shows .54?
In the last column the 2nd one shows 0.48, the 3rd one down shows a beep and a .003 +B -E/C and vice versa. The driver in that column shows .51 +B/-E and .46 +B/-C. Does that difference between the E and C reading mean anything? Does it matter that the second one shows .48 whereas the first one shows .54?
The transistors only will fit one way. The pins are offset, so even though you can plug them in backwards, the screws won't line up and you'll know something is wrong. If you want to make sure they go back into the holes they came from, you can just number them with a Sharpie or something. Just don't use a black one so you can read the part numbers through the marker if needed.
Sounds like you've got a shorted output. Fun times. The normal thing with these is that all of the transistors on a channel need to be the same type. There is an On-Semi part that works nicely as a sub, and its not real expensive. Someone will be along shortly with the magic number I expect. If this were my amp, I think I'd be replacing all of the outputs with new, just so you have both channels matched. I did that on my friend's PL 700 and it wasn't that expensive. Your 400 would be cheaper since its got less parts to buy.
Sounds like you've got a shorted output. Fun times. The normal thing with these is that all of the transistors on a channel need to be the same type. There is an On-Semi part that works nicely as a sub, and its not real expensive. Someone will be along shortly with the magic number I expect. If this were my amp, I think I'd be replacing all of the outputs with new, just so you have both channels matched. I did that on my friend's PL 700 and it wasn't that expensive. Your 400 would be cheaper since its got less parts to buy.
OK I have the results for all 16 transistors. All results reported with positive on B and negative on E, then negative on C. I also did the reverse test but none of the transistors showed anything in reverse except for column 3 third down and column 4 third down.
1: .516/.472
2: .499/.461
3: .513/.472
4: .507/.464
5: .504/.461
6: .508/.477
7: .518/.504
8: .494/.463
9: .518/.494
10: .529/.514
11: .003 BEEP
12: .486/.455
13: .544/.544
14: .48/.48
15: .003 BEEP
16: .51/.46
1: .516/.472
2: .499/.461
3: .513/.472
4: .507/.464
5: .504/.461
6: .508/.477
7: .518/.504
8: .494/.463
9: .518/.494
10: .529/.514
11: .003 BEEP
12: .486/.455
13: .544/.544
14: .48/.48
15: .003 BEEP
16: .51/.46
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I noticed that slight offset, and numbered them with a sharpie as well and sorted them into two piles. What do you guys think of these numbers? Aside from # 11 and 15 do you think the rest are OK despite some variation in their numbers?
What does the blown outputs and the blown supply fuse tell me? What do I want to test for next and why, or do next?
What does the blown outputs and the blown supply fuse tell me? What do I want to test for next and why, or do next?
Also, I know this question is premature because my troubleshooting probably is not complete but I would like to try and order everything I need if I need it from an online business at once to save on shipping so any feedback on what I should do in that regard is welcome. I know I will need at least two outputs and the deoxit d100 spray and d5 spray to clean things (not sure what I should clean and not clean by the way). Do you think those cracked emitter resistors that tested out normal should be swapped or should I wait on those?
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I just soldered on a new power plug to the power cord on the preamp by wrapping the wires, soldering, wrapping in some electrical tape then double shrink wrapped. I hope that is a preferred method...
Now to figure out where the diode 9/10 are. Is there anything else I should be testing?
I assume parts express is where I want to buy those output transistors. When I use deoxit what is the difference in how I use the two sprays and what is the best way to to use them on this particular unit? I have used a contact cleaner to clean scratchy pots in the past but that stuff had a lubricant in it as well.
Now to figure out where the diode 9/10 are. Is there anything else I should be testing?
I assume parts express is where I want to buy those output transistors. When I use deoxit what is the difference in how I use the two sprays and what is the best way to to use them on this particular unit? I have used a contact cleaner to clean scratchy pots in the past but that stuff had a lubricant in it as well.