Alpine MRP-M650 Strange Behavior, Help needed!

[Perry Babin]

I'm assuming that the op-amp cancelling the inverting signal was with the amp operating normally.

Do you get a large spike on the output of the op-amp when the output distorts.

Does it produce the same distortion with no load?

Is the 12v for the driver ICs constant (no dip when the output distorts)?

 

[AlbertLeRoux]

I'm assuming that the op-amp cancelling the inverting signal was with the amp operating normally.

Yes

Do you get a large spike on the output of the op-amp when the output distorts.

Yes, the output basically saturates for the duration that the output signal goes inverted.

Does it produce the same distortion with no load?

Yes

Is the 12v for the driver ICs constant (no dip when the output distorts)?

Yes, if we are talking about the IR2010S p3 (VCC) relative to p15 (VSS).

It seems like there is offset that the op-amp runs out of the ability to control with feedback?

 

[Perry Babin]

The 12v supply goes to pins 2 and 3(+).

If something strange is happening to the high-side B+, it could be due to the top end losing oscillation during the notching or the capacitor for the high-side could be defective but that's not likely to affect two different ICs.

 

[AlbertLeRoux]

The 12v supply goes to pins 2 and 3(+).

This is stable at close to 12V.

If something strange is happening to the high-side B+, it could be due to the top end losing oscillation during the notching or the capacitor for the high-side could be defective but that's not likely to affect two different ICs.

I am afraid I am not following. What can I check to see if this is the case?

Is there a way that I can somehow check if I am losing oscillation? like look at the gate of the output MOSFETs while driving the signal and just seeing if it goes missing?

I noticed that there are two pots for the 2136s any chance that could have any impact?

Thanks for all the help Perry!

 

[Perry Babin]

I 'think' the pots are for DC offset.

Try paralleling a 10uF capacitor across the high-side filter cap to see if it makes a difference.

Did you find and determine if the over-current was causing the problem?

 

[AlbertLeRoux]

So add a 10uF in parallel with the filter capacitor for the high side MOSFET? As in E411 in the M1005 schematic?

I am going back to your manual to learn what I can about IR2010S driver.

It does not look to me like it is the over-current protection. Here is how I looked at it the over current drives the same section used for muting, which prevents +5V going to the emitters of Q303 and Q304. During startup, I can see that there is initially -4.88V at the emitter resistors and then it switches to +4.98 after a few seconds. That is when I would expect rail to rail oscillations to start, but it does not (until a high drive is applied).

 

[Perry Babin]

If you haven't read it, read the page that's just before the type 1 page in the directory.

The diagram says it's a .33uf so you may be able to use something smaller than 10uf. .33 is smaller than I can remember seeing for a high-side supply. C319/320.

 

[AlbertLeRoux]

The page on the latching comparator tool? I will have to build this and test the over current circuit with this!

Thanks again Perry!

 

[Perry Babin]

You may be the first person who has read deeply enough to even find that. It's not needed often but can be useful.

 

[AlbertLeRoux]

I am just grateful that you have documented this type of information for us. There is so much experience in the guide and I am sure I am not the only one that appreciates that!

I have ordered the Service Manual for the amp from PacParts and will continue trouble shooting, once I have that in hand.

The IR2010S seems similar in function as the IR(S)21844S so I am also brushing up on the trouble shooting sections for amps based on the 21844.

Thanks again for all the help!