Feedback when testing Orion 2500D Amp (high pitched sound)

Hey all, so I just picked up an Orion 2500D, looks like it’s never been opened up, powered right up (spark when connecting +12v, assuming caps?) all seems to be working great except I’m getting a high pitched whine regardless of any settings, gain, filters, etc. Same pitch, was louder when first powered on but slowly lowered in volume to a point then stayed, did jump up a lil but while testing amp knobs/switches with music (I did put down some E6000 on components that didn’t have anything against vibrations (attached pic is beforehand) I read these are prone to that type of damage and I can see why after checking inside, I also went thru and cleaned knobs/switches, etc and got a few bugs out lol) I guess the amp sat for a year or 2 before I bought it? Everything works as it should, very happy with it, but that whine is annoying, what should I check to start with the troubleshooting process? This is going to be my main amp, it’s replacing an Alpine MRX-M110 and I plan on keeping it til death (Finally switching over to Orion after running Alpine for last 20 years, always had the itch and now it the time lol) maybe I’m spoiled with how clean Alpine is but I need to figure this out, I’m willing and ready to replace components that are not up to par/could be better/are known to suck/etc so any and all help greatly appreciated. I’m new to amp repair but dig it hardcore, I have a few degrees in PC Hardware and Networking, and am good with my hands, so def ready to dig in before I install it in my car. Thanks all, also anyone have a service manual for this? Trying to learn as much as I can, BCAE site is amazing btw 🖖🏼 Thanks and take care!

P.S. jic, I’m looking to buy end caps and remote knob for this model 😅


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So after my first power cycle (shutdown and restart)I thought it went away but it came back, it’s not as pronounced as it first was but it is still there, cycled a few more times and it always starts as soon as the amp clicks (forgot what that process is when amp clicks at boot up, Class D switching starting up?) but ya, def need to tackle this, as I said earlier not opposed to replacing anything that even remotely needs it, I have a solder station, various fluxes and eutectic solders, small heat gun (not SMD rework type) DMM, cheap o $50 handheld oscilloscope, and a 12.75v 90amp server power supply I converted for home use. I’m in the process of ordering/waiting for delivery of more tools like an ECR? tester, SMD heat station, adjustable Low amperage DC power supply, etc. any other suggestions on what tools I will want for amp repair would be appreciated, I have a few I need to repair and plan on continuing to learn it all 🖖🏼 Thx!
I only tested a subwoofer, all filters full on and full off with various combinations of both, and it was that pitch but I did not notice it oscillating like that, maybe it was so slow and that’s what I perceived as it getting louder/softer but it was VERY slow, so slow it was not noticeable as a wave. I will try to record and post the sound in just a lil bit. For the most part it was constant, with slight reduction in intensity after amp was on for a lil bit, that’s how I perceived it anyway. Brb in just a few with a recording, ty Perry!
I am currently waiting on a proper 20mhz 2ch Oscilloscope, the one I have now didn’t even come with a proper probe and is only a single channel. It should be here next week, shipping to my area has been nuts lately :/ also I tried updating my Sig to list my equipment but could not find a “signature” section for the life of me, I did put a list up in “about me” but it’s not the same quick ref as a sig :/ as soon as I get my proper Oscope I’ll revisit this, really want to figure out what that dang noise is and how to fix it, etc. love learning the troubleshooting procedure, ty Perry :)
When you get the 2 channel scope, do yourself a favor and learn to use it in differential mode.

A differential input uses two inputs to produce a single waveform. The simplest way to get a differential input is to use a differential probe. A differential probe has two signal leads and a mixer amplifier built into it. It feeds the scope a normal signal (a composite of the two signals input into the differential probe). The problem with differential probes is that they're expensive.

The alternative is to use two scope probes and and both inputs of your oscilloscope. This is how you have to set up your scope:

Two probes
Both scope inputs used
Input set to add
Both channels set to DC coupling
Both channels set to 'cal'.
Both vertical amps set to the same voltage
Ch2 input set to invert
Bandwidth limited (works best for most measurements in car amps)
Trace aligned to the reference line on the scope's display
Ground leads for both probes connected together (not always necessary)

After setting up the scope, you need to confirm that it's working as it should. With the vertical amp set to 5v/div, touching the probe that's connected to Ch1 to the positive terminal of your 12v power supply should make the trace deflect about 2.5 divisions up from the reference (like it always does, seen below). Doing the same with the probe connected to Ch2 should make the trace deflect down about 2.5 divisions. Touching both probes to the positive terminal of the 12v power supply should cause no deflection. If it does, something isn't right.

I know that this may not be as simple as the isolated scope but if you take the time to learn it one time (even if it takes an hour or more of your time)N, you have that knowledge and this tool to use for the rest of the time you need to use a scope. Using the analog scope will give you much larger and cleaner waveforms.
Ty for your input Perry, I’m going to look up some differential probes now, and I’ve screenshotted/marked down your instructions, this info is golden and I want to learn it, even if I don’t understand some of it yet 😅 really appreciate you taking the time, I know it mustn’t be easy teaching someone something like this over the internet lol. Soon as my Os ops gets in I’ll def brb.

Gzinc, thx for input bro, as far as the output on my amp it uses 5x irf9640 & 3x fb31n20d per bank, 2 banks per side for a total of 4. I’m assuming they are high and low side of output section? They all tested “good” from my diode setting check with DMM and amp does also work, I haven’t checked anything other then that cuz it does technically work. Are bad output fets that don’t kick on protect known to have this effect on monoblock class d amps? Might just dig a lil deeper, although I’m hoping once my proper Oscope gets in I can figure it out that way.
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