The woofer plays the clipping effect no matter which channel it is hooked up to; left, right, or bridged across left-to-right each of the three configurations make the clipping effect. The same goes with my bench-test speakers. The same clipping sound comes out of both descrete channels.
The only slight variance on this is with the MiniAmp. If the only thing connected to either speaker terminal output is only the miniAmp then sound does NOT clip thoguht the miniAmp. This is a however, because as soon as I put a test speaker in paralell with the miniAmp and on either speaker output both the miniAmp and the test speaker clips. This means the amp sounds clean (w/ the miniamp) until it is driven with even the lightest of speaker loads.
The only slight variance on this is with the MiniAmp. If the only thing connected to either speaker terminal output is only the miniAmp then sound does NOT clip thoguht the miniAmp. This is a however, because as soon as I put a test speaker in paralell with the miniAmp and on either speaker output both the miniAmp and the test speaker clips. This means the amp sounds clean (w/ the miniamp) until it is driven with even the lightest of speaker loads.
Measure the DC voltage on the center legs of the output transistors with and without a speaker. Is there a significant difference in voltage?
Will do.
Side note: I'm looking at possibly getting a oscilliscope for my new hobby 🙂 Not looking to spend very much, so I found an electronic's recycler who has doens of working and not scopes. I asked for a list of some in the $100 range that are working and here is what I got in reply.
Tektronix 485
Kikusui COS2020
Kenwood CS-4125
Are any of these worth having?
Another option was wait for a DSO Nano or DSO Nano v2
Side note: I'm looking at possibly getting a oscilliscope for my new hobby 🙂 Not looking to spend very much, so I found an electronic's recycler who has doens of working and not scopes. I asked for a list of some in the $100 range that are working and here is what I got in reply.
Tektronix 485
Kikusui COS2020
Kenwood CS-4125
Are any of these worth having?
Another option was wait for a DSO Nano or DSO Nano v2
A working 485 for $100 is scary (something has to be3 wrong with it). This is the one I'd pick but it's an old scope and may need new capacitors. I use a 465B and about once a year I have to replace a cap in it but there's no scope I'd rather use.
I know nothing about the others but the kenwood may be the best choice simply because it seems to be the newest.
I'd avoid the DSO. A 'good' DSO is worth having but they're at least $500. In my opinion, for repair work, an analog scope with a CRT display is best. If the scope has DSO capabilities (like the old Tek 2230 and 2232), that's a bonus.
I know nothing about the others but the kenwood may be the best choice simply because it seems to be the newest.
I'd avoid the DSO. A 'good' DSO is worth having but they're at least $500. In my opinion, for repair work, an analog scope with a CRT display is best. If the scope has DSO capabilities (like the old Tek 2230 and 2232), that's a bonus.
On the PC2150 that clips,
I tested the DC output at the power transistors. 11.98v and it doesnt change when the test speaker is connected.
If I apply a low volume 200hz sin wave I get less than .1 volts drop at the power transistors.
Noted on the 485. I'm gonna call the guy back and see why its so inexpensive.
I tested the DC output at the power transistors. 11.98v and it doesnt change when the test speaker is connected.
If I apply a low volume 200hz sin wave I get less than .1 volts drop at the power transistors.
Noted on the 485. I'm gonna call the guy back and see why its so inexpensive.
I called the guy on the Tektronix 485. He said it works OK for being 25-30 years old but his company has not serviced it. He services and sells OScopes by the pallet load it seems and says this unit is below his grade for restoration. I guess that means its visually not sellable for more. He said its tested and works OK. Theck out this listing I found of his on Craigslist. I called and he has LOTs more than just the 34 Tektronix units to my surprise, and the one he said he would sell me was not on his list of 34 junkers.
I told him I dont have a working o-scope to fix a broken one and he laughed.
TEKTRONIX O-SCOPES
I told him I dont have a working o-scope to fix a broken one and he laughed.
TEKTRONIX O-SCOPES
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I still think the kenwood is probably the best choice for you. Ask him to show you that it works and can display a locked waveform on the screen. There should be a calibration test point on the front of the scope to use as a test signal.
Arg sorry I didnt understand you wanted the output transistors (TIP35C) tested. Without test speakers or RCAs connected, I measure 39.8vDC. With just the speakers connected I measure 39.7vDC. Adding in the RCAs with a low volume sin wave of 200hz via RCAs the speaker clips and voltage drops to 39.2vDC. So, about a .75v difference from first to last reading.
He actually wants $140 for the Kenwood and $100 for the Tektronix. I'll check them all out next week cause hes closed now.
He actually wants $140 for the Kenwood and $100 for the Tektronix. I'll check them all out next week cause hes closed now.
Let's put this on hold until you can see if you can get a scope. It would take a lot of guesswork out of the troubleshooting.
Good news! I was able to pick up a Ramsey model **-601 Oscilloscope plus a Topward Function generator from an early retired Electrical Engineer's Tag Sale. The scope I guess is a dual trace, and he gave me a brand new probe plus two that also came with the unit. I'm in the process of learning how to use it, but sofar I am able to get the Function generator working with the RS Mini-Amp and also get some basic frequency's to display on the scope. I also picked up about 2 handfulls of various resistors, several 4 and 8 pin OpAmps, Special hook style clip leads, and a few caps. All for $100 - I think I scored alright!
I'll leave the PC275 alone, but would either of these 8 pin opAmps be suitable for replacement in the PC275's 2068D? Both have the same pin-out layout descriptions as the 2068D. Both are General purpose so my intuition says NO. Looking at the Datasheets show they are very different.
Radio Shack - 1458 Dual Op-Amp
Radio Shack - TL082 Dual Op-Amp
I've put my PC2150 back on the workbench, and clamped down some resistors. Time for me to start testing away!
I'll leave the PC275 alone, but would either of these 8 pin opAmps be suitable for replacement in the PC275's 2068D? Both have the same pin-out layout descriptions as the 2068D. Both are General purpose so my intuition says NO. Looking at the Datasheets show they are very different.
Radio Shack - 1458 Dual Op-Amp
Radio Shack - TL082 Dual Op-Amp
I've put my PC2150 back on the workbench, and clamped down some resistors. Time for me to start testing away!
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On the PC2150 I found a very dirty power supply circuit with my OScope in comparison to the PC275. Connecting the Scope probe shield to battery negative, I probed the center terminal of ALL the power transistors from both amps. While the PC275 shows a nice and clean square wave on the Scope, the PC2150 shows something much more abnormal from any of the ten power transistors.
PC275 - Probing center of Q1
PC2150 - Probing center of Q11
Later on today on the PC2150 I was going to try possibly removing one and then the other bridged/jump connections (J6 or J7) to isolate left and right side power transistors from the circuit and run more tests.
Check out this video for a demonstration of what I did and the OScope's output.
http://s886.photobucket.com/albums/ac65/unclemeat2010/PPC%20PC275/?action=view¤t=VID_20101024_132207.mp4
PC275 - Probing center of Q1
PC2150 - Probing center of Q11
Later on today on the PC2150 I was going to try possibly removing one and then the other bridged/jump connections (J6 or J7) to isolate left and right side power transistors from the circuit and run more tests.
Check out this video for a demonstration of what I did and the OScope's output.
http://s886.photobucket.com/albums/ac65/unclemeat2010/PPC%20PC275/?action=view¤t=VID_20101024_132207.mp4
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Both of those power supply waveforms are normal. The second one is common in amplifiers with regulated power supplies when conditions allow the regulator to reduce the pulse width.
Post photos of the waveforms of the speaker output on the amp (with and without a load).
I'd suggest using the correct op-amp. The ones you have 'may' work but if they don't or there is another strange problem after replacing it, it could cause more confusion.
Post photos of the waveforms of the speaker output on the amp (with and without a load).
I'd suggest using the correct op-amp. The ones you have 'may' work but if they don't or there is another strange problem after replacing it, it could cause more confusion.
PC2150:
The bottom line is reference, from the generator. I set it to make a .5v 100hz frequency and I've attached this signal to Channel A of the scope (Bottom line).
The top line is amplifier output attached to Channel B of the scope, which measures 1.25v on the DVM. I've done my best to match wavelengths on the OScope CRT by adjusting the input voltage of ChanB so that its easy to compare input vs output.
The two signals are matching - Input versus amplifier output. Left and right channels are showing up with the same results.
I see no difference wheather the speaker is connected or not in the top line, therefore I've only posted the one picture.
From the picture it would appear I need my ears examined but I swear I can hear something that I shouldnt. What do you think?
The bottom line is reference, from the generator. I set it to make a .5v 100hz frequency and I've attached this signal to Channel A of the scope (Bottom line).
The top line is amplifier output attached to Channel B of the scope, which measures 1.25v on the DVM. I've done my best to match wavelengths on the OScope CRT by adjusting the input voltage of ChanB so that its easy to compare input vs output.
The two signals are matching - Input versus amplifier output. Left and right channels are showing up with the same results.
I see no difference wheather the speaker is connected or not in the top line, therefore I've only posted the one picture.
From the picture it would appear I need my ears examined but I swear I can hear something that I shouldnt. What do you think?
I ran the above test again, only with lowering the input voltage from the generator to .1v. The PC2150 measured out terminal voltage to .25v.
Again the sin waves do not change when speaker is connected or not...
This time I do notice somehting odd about the top (Amp output) line. I get traces of static in the output of the amplifier. This is the same for both left and right channels.
It would appear this amplifier is outputing a signal variance and the scope only picks it up at very low volume (voltage). My ear can hear it all the time.
Take a look at this 30 second video as my flash cannot get a good snapshot of this noise:
PPC PC275 :: VID_20101024_194814.mp4 video by unclemeat2010 - Photobucket
Again the sin waves do not change when speaker is connected or not...
This time I do notice somehting odd about the top (Amp output) line. I get traces of static in the output of the amplifier. This is the same for both left and right channels.
It would appear this amplifier is outputing a signal variance and the scope only picks it up at very low volume (voltage). My ear can hear it all the time.
Take a look at this 30 second video as my flash cannot get a good snapshot of this noise:
PPC PC275 :: VID_20101024_194814.mp4 video by unclemeat2010 - Photobucket
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Connect the probe ground to the non-bridging terminal for the channel being tested. Disconnect the main scope ground from the battery. Does the noise on the output change?
If you connect the ground for the signal generator to the battery ground, does that make a difference?
What if you use the signal generator you were previously using?
If you connect the ground for the signal generator to the battery ground, does that make a difference?
What if you use the signal generator you were previously using?
I've been running the one scope channel discretely on Channel + and -. I made sure the non-point side what comes off the side of the probe has been attached the Channel unbridged output (Shield?), and the probe center attached to the other terminal.
Connecting ground from generator to battery does change the signal slightly but no audible affect.
The old generator was coming from my laptop. It scopes noisier than anything in any way so I'm setting it aside. Taking a break, will work with it a bit more tomorrow.
Some of these amps have the noise on the output and it causes no audible problems. On this one, the noise in intermittent and that's why it's audible. It appears that the supply may be switching off the power supply pulses. When you get back to it, set it up so that it produces the noise and probe the center legs of the power supply FETs. Set the scope to 2ms and 10v/div. Does the display show a continuous wide band (~2.5 divisions in amplitude) across the display or is the band broken up.
Tested that out.
2mS and 10v/div shows about a 1" thick line on the CRT. I presume this is what you are expecting: Continuous Wide Band . Raising the volume (Amplitude) on the generator changes this line slightly but not enough for the camera.
Setting the sweep to 2uS and 10v/div shows a previous image. Raising the generator output changes this as well, but it never changes to a square wave.
2mS and 10v/div shows about a 1" thick line on the CRT. I presume this is what you are expecting: Continuous Wide Band . Raising the volume (Amplitude) on the generator changes this line slightly but not enough for the camera.
Setting the sweep to 2uS and 10v/div shows a previous image. Raising the generator output changes this as well, but it never changes to a square wave.
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