It used to show DC usually within a few seconds if not immediately. Last night’s test of a minute per transistor was definitely way over the usual threshold.
I already put the pcb on the heatsink but according to the schematic rail caps C47,C48, C52 and C53 all ground to audio ground. Wouldn’t that be the same as Right speaker channel’s negative terminal?
I already put the pcb on the heatsink but according to the schematic rail caps C47,C48, C52 and C53 all ground to audio ground. Wouldn’t that be the same as Right speaker channel’s negative terminal?
The right negative and left positive are the same as the secondary/audio ground.
Is it at all possible that the short could have been something physical in the area of the outputs?
Is it at all possible that the short could have been something physical in the area of the outputs?
I have looked very carefully at the output section, especially Q2-Q6 and found no physical shorts.
So I have the amp on the heatsink as well as the single output transistor on its own heatsink. I then hooked up an audio source and powered up the amp to see if that would force something to trigger the DC voltage. Let it run for a minute but probably could have let it run longer. No DC voltage appeared. Maybe tomorrow I will go looking for an incandescent light bulb. I did find some tiny mini Christmas light bulbs that are incandescent. I could connect it with alligator clips but the wattage is probably too small.
So I have the amp on the heatsink as well as the single output transistor on its own heatsink. I then hooked up an audio source and powered up the amp to see if that would force something to trigger the DC voltage. Let it run for a minute but probably could have let it run longer. No DC voltage appeared. Maybe tomorrow I will go looking for an incandescent light bulb. I did find some tiny mini Christmas light bulbs that are incandescent. I could connect it with alligator clips but the wattage is probably too small.
Try the transistor in various locations, not the same for all transistors.
What's the rating on the speaker you're using?
Did you try touching the halogen (which is incandescent) across the rail?
What's the rating on the speaker you're using?
Did you try touching the halogen (which is incandescent) across the rail?
Found a light bulb but no socket so I soldered the wires to the base . Tested it with rail voltage and it lit up pretty brightly. I then hooked it up to the right speaker terminals for 3mins and it never lit up at all. My speakers are rated at 4 ohm, 70 watts rms. 130w peak.
At this point, I think you have to try all combinations of transistors and locations.
What wattage bulb?
What wattage bulb?
The bulb is a 60w but the base is a non standard B10. Well I guess 20 more combinations to go! Any chance that purchasing an oscilloscope would make troubleshooting this easier or is this trial and error the best way?
To find the problem, there has to be a problem to try to find.
I don't think there's anything a scope could do right now if the amp produces audio when it's not producing DC.
Don't pass up a good deal on a scope, if you find one.
I don't think there's anything a scope could do right now if the amp produces audio when it's not producing DC.
Don't pass up a good deal on a scope, if you find one.
Ok got it. Also is there a reason we are testing for DC with a bulb instead of with the DMM? At first I thought the bulb was like a quick fuse that would blow when it saw DC but that didn’t happen.
If you want to stare directly at a multimeter until it produces DC, feel free. The lamp can be seen while you do other things.
A 40w lamp would have worked as enough of a limiter to insert in series with a speaker to protect it so you could listen to a bit of audio, as well. That's what I use in series with some speakers that I REALLY wouldn't want damaged when testing high power amps. That's why I recommended it. I don't know what your lamp would do, regarding protection.
A 40w lamp would have worked as enough of a limiter to insert in series with a speaker to protect it so you could listen to a bit of audio, as well. That's what I use in series with some speakers that I REALLY wouldn't want damaged when testing high power amps. That's why I recommended it. I don't know what your lamp would do, regarding protection.
Since we tested one location with all the transistors I wanted to test one transistor in all locations. All locations passed after 3mins of testing each. 2mins without any audio input and the last minute with audio. All locations showed similar results. For the first few seconds the mvdc decrease from about 0 until it settles at -3mv. Then once audio is input it starts fluctuating in no discernible pattern but always stays between 0 and -5mvdc. On to test the remaining 16 combinations.
Well, make room in your car for the level and the hard-wired transistor.
You can't use just a few mv on the output for troubleshooting when driving audio into the amp. The meter simply samples the audio when the audio signal is above or below 0v.
Have you tried again heating/cooling/pushing/pulling/flexing?
Has the amp had DC when no screws were in the board?
You can't use just a few mv on the output for troubleshooting when driving audio into the amp. The meter simply samples the audio when the audio signal is above or below 0v.
Have you tried again heating/cooling/pushing/pulling/flexing?
Has the amp had DC when no screws were in the board?
Happy New Year!!! I guess I’ll need some extra trunk space! 😆
So DC has been present both in the heatsink and outside of it. Sometimes removing a transistor solved it intermittently but it soon came back once the transistor was reinstalled. Even when it went away (i.e. when I thought the deoxit fixed it) it soon reappeared after a few days.
Ill try some some of your ideas…just not sure what I can pull and pull and flex on the board?
What about your other idea to install a resistor on each transistor’s base leg and hard wire them all up? Would that be a better test than the location/transistor combinations or the pull, push etc?
By the way I wanted to go ahead and order the TIP142T’s but they are sold out in all US stores? Where can I find them or what’s a substitute? Also do they sell them with the leads already angled at 90 degrees?
So DC has been present both in the heatsink and outside of it. Sometimes removing a transistor solved it intermittently but it soon came back once the transistor was reinstalled. Even when it went away (i.e. when I thought the deoxit fixed it) it soon reappeared after a few days.
Ill try some some of your ideas…just not sure what I can pull and pull and flex on the board?
What about your other idea to install a resistor on each transistor’s base leg and hard wire them all up? Would that be a better test than the location/transistor combinations or the pull, push etc?
By the way I wanted to go ahead and order the TIP142T’s but they are sold out in all US stores? Where can I find them or what’s a substitute? Also do they sell them with the leads already angled at 90 degrees?
Use common sense (don't use a sledge hammer or prybar etc... and you can manipulate anything on the board.
The resistors won't do any good unless the amp malfunctions. It would be an attempt to try to find a location or part that was causing the problem.
Octopart shows a couple of stocking distributors.
You bend the leads yourself.
The resistors won't do any good unless the amp malfunctions. It would be an attempt to try to find a location or part that was causing the problem.
Octopart shows a couple of stocking distributors.
You bend the leads yourself.
Today I tried stress testing it. Heat, cold, shaking, banging heatsink, dropping amp onto table from an inch high, pushed firmly on many components (switches, caps, pots, inductors, driver board, etc.) and turned pots and switches all while powered and nothing. I also let it run for 2 hours. Again nothing. Next up is either audio testing it with speakers or continuing with the location/transistor test. Found some 25w incandescent bulbs. Would those protect my speakers?
25w 120v? Yes but again, you have to use common sense. When the amp stops producing audio because it has rail voltage on the output, you need to shut down the amp. Don't leave it on for hours because you have the lamp in series.
If all else fails, reinstall the outputs in their normal locations and run short wires from any terminals that are broken and reassemble the amp to test as it was to see if the problem returns.
If all else fails, reinstall the outputs in their normal locations and run short wires from any terminals that are broken and reassemble the amp to test as it was to see if the problem returns.
Yes 25w 120v but probably wont need it. Found some cheap $10 car speakers. Will use those and report back.
Used the lightbulb in series and performed a quick 5 second audio test on both channels and they both worked! The right channel is still operating on only 1 transistor. Do you think a good follow up test is to install one transistor at a time using external wires and heatsinks and see what happens?