First thank you to this wonderful forum filled with such great posts and people. I'm new here and loving it! I decided to pull an old soundstream rubicon 404 out of 25 years of storage and see if it works so I could install it in my car. I read many articles, including babin perry's website on amp repair and I am so hooked on the topic. I didn't want to go through the trouble of installing the amp in the car first, so decided to bench-test it with a Dell 500W 18A ATX PC power supply. I combined all the 12v rails and the ground rails and used those to feed 12V and Ground to the amp. I also used one 12V power supply wire for the remote and grounded the PC power supply "power on" green lead. To my excitement, the amp turned on. I then wanted to see if it produced the sweet sound I remembered from long ago so I hooked up a set of MB Quart Comp 6.5" mids/tweets to channels 1-2. Played them at a low then medium volume and they sounded just amazing. They had the fullness and depth I remembered and have been lacking in my car audio since. My audio source was my cell phone with a 3.5" audio jack to RCA adapter. I did have to adjust the amp's input level volts but in barely moving the trimpot I encountered some very loud crackling which was so loud I thought I was going to blow the speaker. I therefore decided to make these level adjustments with the amp off and finally had to leave them at 0.3V.
I then repeated the steps but moved my speakers to channels 3-4. Here I did notice that one channel played lower and that one of the two input level volt trimpots didn't feel smooth like the other. I then proceeded to test a sub on these same channels 3-4 bridged and the 6.5's in channels 1-2 and it worked fine. Played it at medium volume so as not to push the amp too hard. The next day I tried the same last setup and for some reason the sub was barely noticeable but the cones was vibrating slightly. Channels 1-2 were fine. I then tried retesting the 6.5" on channels 3-4 and they worked as before.
So I decided to open the amp up and look for anything odd and since the trimpots were acting strange wanted to take a closer look. Upon inspection, I noticed that the left input level trimpot for channel 3-4 was actually not turning. The plastic piece that is attached to the metal shaft is cracked. See attached picture. so the plastic turns but the shaft doesn't. Also I wanted to measure the resistance of each of the trimpots but they are very hard to reach in such tight spaces, especially the center pin. They appear to be from pictures online to be model CA9 by ACP in Spain. Any tips on how to reach the pins to read the resistance. See attached picture. Could this LEFT trimpot be seized and that is why the plastic broke when it was turned? What does everyone recommend for fixing the shaft and the plastic? Should I apply some lubricant on this trimpot and the others as well? If so, would Deoxit F5 do the trick since the CA9 specs say it's a carbon trimpot?
Lastly, during my inspection, I did notice some white marks or stains around the leads for the crossover switch for channels 3-4. See attached picture. Are these anything to be concerned about?
Thank you all for reading my long post. Any and all help is truly appreciated. Also, what are everyone's thoughts on how I'm powering my amp with the ATX power supply? Is this an acceptable power supply for temporary testing? I don't plan on using it long-term this way. Once I can confirm it all works I will then install it in my car.
I then repeated the steps but moved my speakers to channels 3-4. Here I did notice that one channel played lower and that one of the two input level volt trimpots didn't feel smooth like the other. I then proceeded to test a sub on these same channels 3-4 bridged and the 6.5's in channels 1-2 and it worked fine. Played it at medium volume so as not to push the amp too hard. The next day I tried the same last setup and for some reason the sub was barely noticeable but the cones was vibrating slightly. Channels 1-2 were fine. I then tried retesting the 6.5" on channels 3-4 and they worked as before.
So I decided to open the amp up and look for anything odd and since the trimpots were acting strange wanted to take a closer look. Upon inspection, I noticed that the left input level trimpot for channel 3-4 was actually not turning. The plastic piece that is attached to the metal shaft is cracked. See attached picture. so the plastic turns but the shaft doesn't. Also I wanted to measure the resistance of each of the trimpots but they are very hard to reach in such tight spaces, especially the center pin. They appear to be from pictures online to be model CA9 by ACP in Spain. Any tips on how to reach the pins to read the resistance. See attached picture. Could this LEFT trimpot be seized and that is why the plastic broke when it was turned? What does everyone recommend for fixing the shaft and the plastic? Should I apply some lubricant on this trimpot and the others as well? If so, would Deoxit F5 do the trick since the CA9 specs say it's a carbon trimpot?
Lastly, during my inspection, I did notice some white marks or stains around the leads for the crossover switch for channels 3-4. See attached picture. Are these anything to be concerned about?
Thank you all for reading my long post. Any and all help is truly appreciated. Also, what are everyone's thoughts on how I'm powering my amp with the ATX power supply? Is this an acceptable power supply for temporary testing? I don't plan on using it long-term this way. Once I can confirm it all works I will then install it in my car.
The questions being buried in larger paragraphs means I will miss some.
I've never used F5. Only D5. F5 may be OK if it will flow down into the pot. As far as I know it contains more lubricant so it doesn't cause faders to freeze.
The ATX supply is generally OK.
Use an allen wrench to reach all pots in the stack. The shafts are sometimes available on ebay. Someone here may have some.
You will have to align all pots in the stack before using the amp. If misaligned, it can sometimes cause an amp to oscillate which can damage speakers or possibly the amp.
I've never used F5. Only D5. F5 may be OK if it will flow down into the pot. As far as I know it contains more lubricant so it doesn't cause faders to freeze.
The ATX supply is generally OK.
Use an allen wrench to reach all pots in the stack. The shafts are sometimes available on ebay. Someone here may have some.
You will have to align all pots in the stack before using the amp. If misaligned, it can sometimes cause an amp to oscillate which can damage speakers or possibly the amp.
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Wow what an honor to have you respond Perry. Thank you for your amazing amp repair tutorial. I've read it over and over. I'm seriously considering purchasing the full package just because I love to learn about how things work. The pictures were just attached. Sorry about that.
The allen wrench idea will definitely work. I'll give it a shot tonight. I haven't purchased the F5 yet, but got the idea from reading this. Would either F5 or D5 cause any issues if it leaks onto the board or other components? How do you recommend I apply it to such small components?
As for the shaft I can't find an exact match on ebay. According to the datasheet none of the shafts match the one Soundstream used. As you can see the soundstream shaft's plastic part is all the same diameter top to bottom. The ones I find on ebay and in the datasheet have a larger diameter at the bottom which I doubt will fit the hole in the metal case of the amp.
Lastly, the reason I wanted to test the trimpots resistance was to make sure they are working. I don't think they have any misalignment because I was very careful pushing/pulling out the shaft. Any hints on how to test the resistance with such little room to reach the trimpots' legs with a multimeter? Are there any points or traces on the board that I can use?
The allen wrench idea will definitely work. I'll give it a shot tonight. I haven't purchased the F5 yet, but got the idea from reading this. Would either F5 or D5 cause any issues if it leaks onto the board or other components? How do you recommend I apply it to such small components?
As for the shaft I can't find an exact match on ebay. According to the datasheet none of the shafts match the one Soundstream used. As you can see the soundstream shaft's plastic part is all the same diameter top to bottom. The ones I find on ebay and in the datasheet have a larger diameter at the bottom which I doubt will fit the hole in the metal case of the amp.
Lastly, the reason I wanted to test the trimpots resistance was to make sure they are working. I don't think they have any misalignment because I was very careful pushing/pulling out the shaft. Any hints on how to test the resistance with such little room to reach the trimpots' legs with a multimeter? Are there any points or traces on the board that I can use?
Why do you want to test their resistance?
The only way to do it reliably would be to remove them from the circuit (not recommended) because the circuit will skew readings.
You may want to have all shafts in place but after they're set, they serve no purpose. For adjustments, you can use an allen wrench.
Apply a drop of the D5 (or whatever you use) to the top of the pot where the plastic meets the metal and gently work the body of the pot back and forth. You can also apply a drop into the hole where the adjuster passes through the body of the pot if you need to get more into the pot. The contact cleaner should flow down into the pot. Then (with the amp off), work the pot through its entire range 30, 40, 50 times.
D5 won't cause any problems on the board but you shouldn't apply more than needed.
The only way to do it reliably would be to remove them from the circuit (not recommended) because the circuit will skew readings.
You may want to have all shafts in place but after they're set, they serve no purpose. For adjustments, you can use an allen wrench.
Apply a drop of the D5 (or whatever you use) to the top of the pot where the plastic meets the metal and gently work the body of the pot back and forth. You can also apply a drop into the hole where the adjuster passes through the body of the pot if you need to get more into the pot. The contact cleaner should flow down into the pot. Then (with the amp off), work the pot through its entire range 30, 40, 50 times.
D5 won't cause any problems on the board but you shouldn't apply more than needed.
Thank you for your help Perry. I wanted to check the resistance because of the issues I found with channels 3 and 4. First issue was when I tested them in stereo with the 6.5's and one speaker sounded noticeably louder than the other even though they were set to the same maximum input level. Second issue was when I tested these same channels in bridged mode and the sub volume mysteriously changed overnight from working fine at medium volume to making no sound and barely vibrating the sub's cone. (Important to note that I didn't touch anything in the setup overnight. I shut it down, left it on the bench and turned it on the next day to find it was no longer working normal). These issues may be attributed to something other than the trimpots but since I had the amp open thought it was a good idea to check their resistance. If I have to remove the trimpots to do this, then I rather wait and see if the lubrication and the allen wrench solves the problem. Is the spray bottle D5 the one you recommend? This one
Thank you Perry. Will give your recommendations a try and report back. Also will investigate the marks around S102 a little further and/or try to take a better picture. I don't want to stress the amp because of the ATX supply while testing. Any way to know if I'm pushing it too hard? I checked the AC voltage while driving the speakers on the 12v screw (I believe this is the B+ terminal in your tutorial) and the ground screw. It read a constant 12v. Should I add a 10amp fuse between the ATX power and the amp like you mention in your tutorial?
The 10/15 amp fuse is to help protect the amp's components when testing, especially when the amp is out of the heatsink. It won't do any harm to have it inline and may be a good idea if you're poking around in the amp while it's powered up.
The ATX supply is OK. It won't do any harm. Depending on its ratings, it may shut down if you drive the amp too hard but it won't hurt the amp.
Can you rub the white marks off of the board with your finger or a cotton swab?
The ATX supply is OK. It won't do any harm. Depending on its ratings, it may shut down if you drive the amp too hard but it won't hurt the amp.
Can you rub the white marks off of the board with your finger or a cotton swab?
Thank you Perry. Now not only do they start and end at the same point but the shaft marker goes through the complete range of 0.3v to 5v. Should I D5 all the pots since I have it open or is it better to leave them alone if they are working?
Also regarding the white stains. Not sure what it is but it’s not a paste unless it’s dried or caked on because it would only come off by scraping it with my nail. I attached another photo.
I will bench test it tomorrow once I get some 10/15 fuses and see how the switches are doing but after noticing that the pots on the left channel of 3-4 were misaligned I am now thinking that may have been the problem.
Also regarding the white stains. Not sure what it is but it’s not a paste unless it’s dried or caked on because it would only come off by scraping it with my nail. I attached another photo.
I will bench test it tomorrow once I get some 10/15 fuses and see how the switches are doing but after noticing that the pots on the left channel of 3-4 were misaligned I am now thinking that may have been the problem.
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I wouldn't apply anything if there is no problem.
For the white substance, I wouldn't be concerned about it. Heatsink compound can harden but I've never seen the compound in SS amps harden.
If there are no problems and you don't need to move the switches, you may want to leave them as is. Replacements can be difficult to find. You can generally clean them but it's risky because you typically have to disassemble them and clean them mechanically.
With 10/15 amp fuses, you will only be able to test at low power. The low value fuses are typically for use when testing when the amp is out of the sink or when doing something risky.
For the white substance, I wouldn't be concerned about it. Heatsink compound can harden but I've never seen the compound in SS amps harden.
If there are no problems and you don't need to move the switches, you may want to leave them as is. Replacements can be difficult to find. You can generally clean them but it's risky because you typically have to disassemble them and clean them mechanically.
With 10/15 amp fuses, you will only be able to test at low power. The low value fuses are typically for use when testing when the amp is out of the sink or when doing something risky.
Ok Ill try to not mess with the switches too much. How about if I want to test the amp a little harder once I see that the channels and pots are working fine. I was reading to use a DC regulated power supply but they seem to be very expensive in the 50-100A range. Another option I read could work and maybe be more affordable is a used car battery and a float or tickle charger to recharge it between tests.
Cyano adhesives don't stick to plastic very well. Good if it holds but be careful when turning it.
I don't know if it will work on this plastic but a chemical welding adhesive that melts the plastic like Weld-on 16 may have worked. Weld-on 4 may also have worked but evaporates so quickly that it can be difficult to work with.
I don't know if it will work on this plastic but a chemical welding adhesive that melts the plastic like Weld-on 16 may have worked. Weld-on 4 may also have worked but evaporates so quickly that it can be difficult to work with.