I certainly will. I'm getting a couple of 2068; one for each amp.
In the future, I'll be working on a Hifonics Generation X Thor amp. I had Steve estimate it and he quoted me way too much to fix. I'll be posting about that one probably next week. Its a fantastic dinosaur!
Thanks again my friend, for sticking with me and pulling us both out of this. You are a mentor and asset to the community; for which I hope it is enticing for you as it is for everyonne.
In the future, I'll be working on a Hifonics Generation X Thor amp. I had Steve estimate it and he quoted me way too much to fix. I'll be posting about that one probably next week. Its a fantastic dinosaur!
Thanks again my friend, for sticking with me and pulling us both out of this. You are a mentor and asset to the community; for which I hope it is enticing for you as it is for everyonne.
Update on the PC275. I got the dual opAmp (2068D) from Mouser today and carefully installed. Unfortunately the right channel still experiences the whisting with no RCAs and speakers connected via the miniAmp, and buzzing with speakers and signal playing. I'm in the process of tracing things with the scope this time; as I have not done that yet before. Remember this amp was able to pick up FM radio broadcast over the right channel via the miniAmp.
Just like before, if I touch the 2068D opAmp with the mini connected to the right channel, I get obnoxious buzz like I'm playing Operation.
So far, I've determined that the opAmps all seem fine, plus the LP/HP crossover does not change the noise output at the speaker terminals. Likewise with any of the other controls. I'm poking my way through the amp and will let you know if I find anything from what I've already learned.
What exactly does the SG3525 and 4N25 do?
Just like before, if I touch the 2068D opAmp with the mini connected to the right channel, I get obnoxious buzz like I'm playing Operation.
So far, I've determined that the opAmps all seem fine, plus the LP/HP crossover does not change the noise output at the speaker terminals. Likewise with any of the other controls. I'm poking my way through the amp and will let you know if I find anything from what I've already learned.
What exactly does the SG3525 and 4N25 do?
The 3525 drives the power supply FETs.
The 4N25 is for muting and LED drive if I'm not mistaken.
Compare the following image to the 275. Are there any components near the 2068 missing in your amp?
http://www.bcae1.com/temp/IMG_7863.JPG
The 4N25 is for muting and LED drive if I'm not mistaken.
Compare the following image to the 275. Are there any components near the 2068 missing in your amp?
http://www.bcae1.com/temp/IMG_7863.JPG
Looked for a few minutes, and actually; yes Mine is missing 2 ceramic capacitors near Q47 - Next to C84 I have a blank spot at C83. Your image is showing 2 capacitors there at C84 and C83.
Likewise on the other side of the amp; Near Q6 I am missing one cap. C1 is populated and C2 is missing. Your image shows two caps at C1 and C2.
The caps on my PCB are 56 picofarads. What are yours?
Also I see yours has mostly black electrolitic caps where mine are blue.
Board revision B-2075-0002
Likewise on the other side of the amp; Near Q6 I am missing one cap. C1 is populated and C2 is missing. Your image shows two caps at C1 and C2.
The caps on my PCB are 56 picofarads. What are yours?
Also I see yours has mostly black electrolitic caps where mine are blue.
Board revision B-2075-0002
The ceramic caps that you have installed are the same. The missing ones are 33pf. Many times, small capacitors like these are used to limit the frequency response of an amp and prevent the types of problems you're experiencing. I don't know if they will solve your problem but I'd try installing them.
This is also rev2 18 - 2075 - 0002.
This is also rev2 18 - 2075 - 0002.
While jamming to Ozzy Ozborne through the miniAmp connected to right speaker terminal output (FM Radio in Atlanta - Not even kidding!), I noticed something peculiar about C62; a 33pF Cap next to pins 5-6-7 of 2068D. This cap is actually making the noise when touched, and not the 2067D.
I went one step further with C62, and with a very small insulated screw driver seperately touched the base of C62 where its soldered into the PCB. From there if I touch the screw driver with my finger; the miniAmp goes crazy, but only when I'm touching the base of C62 just next to the 2068D pin 5. The base of C62 near 2068D pin 7 does not make any noise when touched.
Bad cap at C62? Whats under the PCB connected to this cap, if anything.
I went one step further with C62, and with a very small insulated screw driver seperately touched the base of C62 where its soldered into the PCB. From there if I touch the screw driver with my finger; the miniAmp goes crazy, but only when I'm touching the base of C62 just next to the 2068D pin 5. The base of C62 near 2068D pin 7 does not make any noise when touched.
Bad cap at C62? Whats under the PCB connected to this cap, if anything.
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I resoldered it and no difference. Legs look -ok-; a little cracked at the base but a lot of the small ones are. I notice C62 has the slightest little buldge on it but it may be manufacturing defect.
Only a metal object where I can touch and conduct whatever from my finger. Seems if I do the same with the screw driver at C83 (the missing 33pf cap) I also get the noise.
Looks like I'm going to buy a pack of 33pf caps. I think RS still sells them.
I'm gonna clip C62 off the board and see if anythings difference.
EDIT: Wow - Lots more FM radio and general noise with C62 cap removed.
Only a metal object where I can touch and conduct whatever from my finger. Seems if I do the same with the screw driver at C83 (the missing 33pf cap) I also get the noise.
Looks like I'm going to buy a pack of 33pf caps. I think RS still sells them.
I'm gonna clip C62 off the board and see if anythings difference.
EDIT: Wow - Lots more FM radio and general noise with C62 cap removed.
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I measured the resistance on the gain and qBass pots. They are supposed to be 10k each, but the qBass control is only measuring 7k from edge pin to edge pin on half of it, and 9.2k on the other half. I think it might be bad, and I'm probably going to take it off the board.
I dont mean to jack around too much, but I will never be needing qBass control with this amp as it will be running door speakers in high-pass mode. Is there some way with common resistors I can lock this part to 'off'? I was thinking of soldering 2 pins together, and using a pair of 10k resistors.
Center of this picture are 6 pins. I was thinking of shorting middle pins to the top which already reads 1ohm, and then placing a pair of 10k resistors from the middle to the bottoms.
Currently, middle to top sets read 1ohm, and middle to bottom sets is odd/not right. 7k on left, and 9.2k on the right. Again, this is reading the qBass control pot.
I dont mean to jack around too much, but I will never be needing qBass control with this amp as it will be running door speakers in high-pass mode. Is there some way with common resistors I can lock this part to 'off'? I was thinking of soldering 2 pins together, and using a pair of 10k resistors.
Center of this picture are 6 pins. I was thinking of shorting middle pins to the top which already reads 1ohm, and then placing a pair of 10k resistors from the middle to the bottoms.
Currently, middle to top sets read 1ohm, and middle to bottom sets is odd/not right. 7k on left, and 9.2k on the right. Again, this is reading the qBass control pot.
Just getting back to this this evening. I actually did go ahead and remove the qBass pot. I have a pretty nice soldering iron which heats and sucks at the same time. It got the pot out in about 2 minutes. It works well with ICs too. I'll likely put the pot back in a little later.
So the problem isnt with the pot as onthe bench it measures correctly. I did power the amp on without it installed and the noise still happens.
I'm still trying to trace through to the problem however.
So the problem isnt with the pot as onthe bench it measures correctly. I did power the amp on without it installed and the noise still happens.
I'm still trying to trace through to the problem however.
I thought this was one of the plastic body pots. It's virtually impossible to remove many of the plastic body pots (the ones that sit flat on the board) without damaging them. The damage isn't always immediately apparent. They generally become intermittent and they're not repairable. Did you install the 33pf caps?
Yes I put the 33pF caps in but they didnt fix it.
Guess what?? Happy day indeed! After testing a bit more, I found that although touching the board made the noises, I didnt realize that audibly the output was actually clean; until I pushed tones through the speakers from my generator. The solution is not 100% perfect electrically thinking; but....
The PC275 amp is FIXED! No-longer does the qBass pot live inside; and theres nothing in its place on the PCB - just empty holes. She's clear as day with that sucker removed on the bench and now back in my car. I was actually able to activly play a tone and listen to the amp's right channel go from clean - to dirty - to clean; just by gently placing the qBass pot back in it's spot. I've even gone so far as to re-install the amp in my car. Right channel is clean, Left channel is clean. All without the qBass pot installed, and nothing in its place.
Go figure! I'm happy as a clam!
Ive still got parts on order for it though. I had to beef up an order minimum at Goldmine-elec to get some opAmps, so I bought a bunch of transistors to replace in the PC275. I actually dont think I'm going to open it again so now I have a bunch of spare parts for the hobby.
Perry, Thank you for your help with everything. I'll post again when I finally replace the PC2150's bad opamp with the results.
For now, keeping fingers crossed that a missing qBass pot doesnt effect longevity.
Guess what?? Happy day indeed! After testing a bit more, I found that although touching the board made the noises, I didnt realize that audibly the output was actually clean; until I pushed tones through the speakers from my generator. The solution is not 100% perfect electrically thinking; but....
The PC275 amp is FIXED! No-longer does the qBass pot live inside; and theres nothing in its place on the PCB - just empty holes. She's clear as day with that sucker removed on the bench and now back in my car. I was actually able to activly play a tone and listen to the amp's right channel go from clean - to dirty - to clean; just by gently placing the qBass pot back in it's spot. I've even gone so far as to re-install the amp in my car. Right channel is clean, Left channel is clean. All without the qBass pot installed, and nothing in its place.
Go figure! I'm happy as a clam!
Ive still got parts on order for it though. I had to beef up an order minimum at Goldmine-elec to get some opAmps, so I bought a bunch of transistors to replace in the PC275. I actually dont think I'm going to open it again so now I have a bunch of spare parts for the hobby.
Perry, Thank you for your help with everything. I'll post again when I finally replace the PC2150's bad opamp with the results.
For now, keeping fingers crossed that a missing qBass pot doesnt effect longevity.
I do feel bad that its not properly fixed, but then again it sounds great. I drove around for a bit and dont hear any foulness out of anything. Its one chapter closed thats for sure.
I did trace things until my eyes started going googly. When I get them, I might try replacing the 14 pin opAmps because two of the input pins on one of them were quite noisy. The opAmp near the ceramic pF caps is the one I'm talking about.
The main point from the qBass control which had most of the noise runs up to C64 cap, and then jumps over to resistor, then it branches out in numerous directions. I kind of gave up on finding the ghost for now.
I did trace things until my eyes started going googly. When I get them, I might try replacing the 14 pin opAmps because two of the input pins on one of them were quite noisy. The opAmp near the ceramic pF caps is the one I'm talking about.
The main point from the qBass control which had most of the noise runs up to C64 cap, and then jumps over to resistor, then it branches out in numerous directions. I kind of gave up on finding the ghost for now.
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PC2150 is officially FIXED!
parts list:
1x LM8837N
4x TIP35C
4x TIP36C
32x 0.68ohm 3w Emmitter resistors.
Really when it came down to it I only needed to replace the ONE LN837N OpAmp; however due to this being my first experience I had popped one of the original TIP35C output transistors and decided to replace all emiters AND output transistors for new, and possibly better parts (OnSemi brand)
Amp sounds great! Lower gains than before in the car
Thanks perry!
parts list:
1x LM8837N
4x TIP35C
4x TIP36C
32x 0.68ohm 3w Emmitter resistors.
Really when it came down to it I only needed to replace the ONE LN837N OpAmp; however due to this being my first experience I had popped one of the original TIP35C output transistors and decided to replace all emiters AND output transistors for new, and possibly better parts (OnSemi brand)
Amp sounds great! Lower gains than before in the car
Thanks perry!
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