I have two of these in for repair from a friend.
First amp powers and will play but at very high unloaded drive signal when the amp indicates about 3/4 amplification the upper waveform on the outputs squares out. Briefly the amp will draw excessive amperage out of my small PS set limit (5A) and the amp will reset. During this problem, some of the small LEDs on the ZED logo will flicker off.
IRS20957 driving IRFP4227
Type 3 amp
How can I check the output circuits in this, or should I look for a replacement 20957?
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Second amp had an open 1-ohm resistor very near the IRS20957, and also two small caps - one shorted down to 25 ohms. I replaced the caps and installed a new 1-ohm resistor. Most other components in this area seem OK from what I can measure on the PCB. Ohming out the 20957 devices between both amps made me think this 20957 is OK, but maybe not. Amp powers on with 4.5vDC on speaker terminals, and the ZED logo is only 15% lit up once the amp fully boots (But it DOES flash fully during soft start) - I think its indicating some kind of problem but have no idea what the ZED logo LEDs are trying to say. On this amp I'm thinking the 20957 is not operating correctly.
First amp powers and will play but at very high unloaded drive signal when the amp indicates about 3/4 amplification the upper waveform on the outputs squares out. Briefly the amp will draw excessive amperage out of my small PS set limit (5A) and the amp will reset. During this problem, some of the small LEDs on the ZED logo will flicker off.
IRS20957 driving IRFP4227
Type 3 amp
How can I check the output circuits in this, or should I look for a replacement 20957?
-------------------------------
Second amp had an open 1-ohm resistor very near the IRS20957, and also two small caps - one shorted down to 25 ohms. I replaced the caps and installed a new 1-ohm resistor. Most other components in this area seem OK from what I can measure on the PCB. Ohming out the 20957 devices between both amps made me think this 20957 is OK, but maybe not. Amp powers on with 4.5vDC on speaker terminals, and the ZED logo is only 15% lit up once the amp fully boots (But it DOES flash fully during soft start) - I think its indicating some kind of problem but have no idea what the ZED logo LEDs are trying to say. On this amp I'm thinking the 20957 is not operating correctly.
I didn’t think so but I can try to raise the limit on it more tomorrow. The amp was only pulling 2A until the upper half squared-out and only then did it drag to the set limit of the small ps. No current limiter inline.
I increased the max PS output to 10A and also replaced the IRS20957 and no difference. The upper waveform unloaded hits massive clipping at about 2/3 signal input and the amp briefly draws out to 10A and then resets.
I'll try.
In the meantime, these two amps have what look to be several dozen post-assembly modifications. On amp1, there is no REG4, whereas amp2 has a REG4. 7815. I did not remove amp 2 from the sync, but amp1 has a PF2203-20K, 35w resistor under the board sandwiched in between rails. This resistor was getting extremely HOT (by design). I actually removed it and to be honest the amplifier is starting to actually work a little better on output clarity. I am now able to bring the amp up most of the way to clipping unloaded without having it freak out as badly.
Do you know if these amps have some sort of variable rail voltage? Wonder if the positive rail is having trouble keeping up with the input signal.
I think I'll fully sync and test under higher load to see what is what... The boards are black, and also covered with some kind of marine coating making it very challenging.
In the meantime, these two amps have what look to be several dozen post-assembly modifications. On amp1, there is no REG4, whereas amp2 has a REG4. 7815. I did not remove amp 2 from the sync, but amp1 has a PF2203-20K, 35w resistor under the board sandwiched in between rails. This resistor was getting extremely HOT (by design). I actually removed it and to be honest the amplifier is starting to actually work a little better on output clarity. I am now able to bring the amp up most of the way to clipping unloaded without having it freak out as badly.
Do you know if these amps have some sort of variable rail voltage? Wonder if the positive rail is having trouble keeping up with the input signal.
I think I'll fully sync and test under higher load to see what is what... The boards are black, and also covered with some kind of marine coating making it very challenging.
From the owner's manual:
All amplifiers feature a two stage power supply for increased efficiency
All amplifiers feature a two stage power supply for increased efficiency
I believe the 2k 35W resistor is in circuit to pull the rail voltage down from full when the amplifier comes down. I can observe +-55 ~ +-81vDC rail.
OK so somehow amp2 started not putting out 4.5vDC on speaker terminals.
Now both amps are doing exactly the same problem as previously described with amp1. Unloaded at 3/4 input the upper waveform notches out. WHen providing clean audio, the amplifiers appeared to be stable out to clipping however....
Under 2-ohm load is a different story. At about 10% input 8A draw both amps get nutty output under audio and generated signals. Here is an output image on a 1k sign wave at 1vDiv-10x on the probe. It’s rapidly cycling output on / off under load hence the single probe is showing a flat line through the sign wave.
OK so somehow amp2 started not putting out 4.5vDC on speaker terminals.
Now both amps are doing exactly the same problem as previously described with amp1. Unloaded at 3/4 input the upper waveform notches out. WHen providing clean audio, the amplifiers appeared to be stable out to clipping however....
Under 2-ohm load is a different story. At about 10% input 8A draw both amps get nutty output under audio and generated signals. Here is an output image on a 1k sign wave at 1vDiv-10x on the probe. It’s rapidly cycling output on / off under load hence the single probe is showing a flat line through the sign wave.
Attachments
Output fets are being driven by push-pull drivers. Each of the 4 fets have 2 drivers. Do any of these readings look funky? Referencing amp general ground.
IRS20957
1; 10.4
2; 10.4
3; 2.4
4; -1.2
5; -nc-
6; -41.2
7; -43.6
8; -55.6
9; -55.6
10; -50.0
11; -43.6
12; -nc-
13; -1.2
14; 5.2
15; 10.8
16; 3.2
IRS20957
1; 10.4
2; 10.4
3; 2.4
4; -1.2
5; -nc-
6; -41.2
7; -43.6
8; -55.6
9; -55.6
10; -50.0
11; -43.6
12; -nc-
13; -1.2
14; 5.2
15; 10.8
16; 3.2
FETs in or out?
It appears that there is an offset between the primary and secondary grounds. Connect a load across the speaker terminals and use pin 4 for the reference.
Repost new voltages.
Post a photo of the components in the audio drive section.
It appears that there is an offset between the primary and secondary grounds. Connect a load across the speaker terminals and use pin 4 for the reference.
Repost new voltages.
Post a photo of the components in the audio drive section.
Fets are in and entire amp is synced. 4-ohm load connected. No input signal.
Negative speaker terminal is connected directly to amp ground.
20957
1; 10.3
2; 10.3
3; 2.08
4; -reference-
5; -nc-
6; -43.5
7; -43.4
8; -55.1
9; -55.1
10; -49.5
11; -43.3
12; -nc-
13; 0.065
14; 5.08
15; 10.49
16; 2.90
Negative speaker terminal is connected directly to amp ground.
20957
1; 10.3
2; 10.3
3; 2.08
4; -reference-
5; -nc-
6; -43.5
7; -43.4
8; -55.1
9; -55.1
10; -49.5
11; -43.3
12; -nc-
13; 0.065
14; 5.08
15; 10.49
16; 2.90
I believe so for many amps but Im not so sure about these amps. These amps could both have identical problems. BOTH measure the exact same voltages on 20957. The amp without REG4 is also lighting up LED303 about half the time I power it up. When LED303 is lit that amp will not pass audio.
I don't have any known good voltages on these but the internal voltage reference on pin 6 is supposed to be 5.1v above the negative rail (pin 9).
You may also have an open resistor between pin 7 and pin 9.
Did you try replacing the IC?
You may also have an open resistor between pin 7 and pin 9.
Did you try replacing the IC?
In one of the amps, yes I did change that IC. That did not change the issues. Pin 2: CSD is at 10.3v. When the amp shuts down, this pin goes to 6v.
What about the NJM360? This comparator has only 2 inputs with 2 outputs. I'm not following exactly why both outputs would be high.
NJM360
1; -nc-
2; -0.013
3; -0.019
4; -5.12
5; 0 -reference-
6; 2.291
7; 2.190
8; 5.07
NJM360
1; -nc-
2; -0.013
3; -0.019
4; -5.12
5; 0 -reference-
6; 2.291
7; 2.190
8; 5.07
When the LM361 (common differential comparator) had 2 high outputs, it was defective.
In the amp that you replaced the IC in, is pin 6 more than about 5v above the negative rail (pin 9)?
Are you using pin 4 for the reference when you measured the voltage on pin 2?
In the amp that you replaced the IC in, is pin 6 more than about 5v above the negative rail (pin 9)?
Are you using pin 4 for the reference when you measured the voltage on pin 2?
I’ll check lm360 more thoroughly on both amps, but if the outputs are both high is that a problem?
Yes pin 6 is about 12v more still with the replaced irs.
I measured several directions between pin 7 & 9 and they’re connected through resistors which are measuring ok. Pin 7 is also connected to several output buffers.
Yes I’ve been referencing pin 4 for readings since suggested.
Yes pin 6 is about 12v more still with the replaced irs.
I measured several directions between pin 7 & 9 and they’re connected through resistors which are measuring ok. Pin 7 is also connected to several output buffers.
Yes I’ve been referencing pin 4 for readings since suggested.