How to bypass or adjust or modify an over current protection circuit on JVC 7042s receiver?

Hello, let me start with I picked up this nice condition JVC receiver because it hosts a 130w per channel amplifier. However when I start turn the volume up and I get to an almost perfect level of "loud" but not "distorting" (it's not even nearing distortion, so I can tell there is still lots of room for more volume...) but when I pump it up a bit more the over current protection kicks in. (I have about 14 other receivers here all around 100w to 110w and they all drive these same speakers much louder with more punch).
I can tell whoever set this protection circuit up must have leaned towards safety over performance, because the heatsinks are not even hot.

I opened it up and I thought I saw "temperature sensors" thermistor's near the amp chips, with the "left channel" one being bent very close to the amp IC (I bent it back like the others) and I assumed ok now I'll get more volume. But I got the same cut out at around the exact same volume. So I installed a large PC fan on the heatsink to keep it cool... and it cut off at the same volume (I might add this is not digital/display volume on the unit - but the same audible volume).

So there is something causing the cut off to cut out long before it's technical abilities are overloaded/tapped.
I'd like to figure out where the over-current protection circuit might be, and possibly remove it and or change it's value so it does not cut out so soon before the peak performance of this unit has had a chance.

I might add some key points:
The speakers I am using are in A+B combination (4 speakers) / the unit states in the manual use only 8 or 16ohm speakers at each terminal, however both pairs of my speakers being used are 4ohms. Technically speaking I get away with using these same speakers on other receivers fine (making sure to always use a good fan to keep the heatsink cool) and there is no issue driving them hard for extended periods. I have one Sony 110w which only has Speaker A terminals and it's got a hard switch to select 4ohm or 8ohm, so I set it to 4ohm and installed the 2x 4ohm speakers totalling 2ohms and ran it for 10mins, the heatsink got so hot I panicked and installed a permanent fan. Now it runs fine 2ohm speakers testing for a solid hour at loud volume, no issues (and stays just warm now).
So out of all these other receivers I've run these same speakers off - this is the only unit having "issues" and I think it's simply because they set the cut off limit too low.

I've included some images, in the one image I have two arrows, the Red Arrow points to a trimmer that is on only found on the L / R channels amp boards. Judging from the type of wires running to these pcb's I'm assuming these pot/trimmers are a "line input levels" (for gain up or down). However I'm not sure how these circuits were designed, and more importantly what an over-current circuit looks like (and or where they would locate it) so these might also be the "cut off voltage trimmers?" I dunno hence why I am posting here.

I've also included a potential "sectioned out pcb" that looks like it might be regulating the voltage... so perhaps this is the over current circuit?

But lastly, I also marked a "yellow arrow" to what I originally thought was temperature sensors doing the cut off....(it looks an awful like a Thermistor to me) AND the PCB label for this part is literally "TH731" further indicating it's "THermal" sensor, so perhaps I can just swap these out with another value? Or put a resistor in their place? But what value... hmmm.

Any help would be greatly appreciated!


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The part your yellow arrow points to is a thermistor and it is part of the bias current temperature compensation. The preset is for setting bias current. Do not alter the presets unless you know what you are doing.

Over current sensing is totally conventional and is done by monitoring volt drop across the output transistor emitter resistors. Thermistor and over current circuit highlighted.

It sounds like you are pushing this quite hard, maybe you are expecting to much :)

Screenshot 2024-04-02 194510.png
(I did update my original post as I noted when I looked at these Thermistor the PCB labels them as TH### indicating Thermistor.)

Anyways, in that all my other 100w receivers can push these speakers louder I was expecting this 130w one to drive them better since it's 130w per chan.
And yes I love to pound music... I normally run a much higher end 180w Pioneer receiver as an amp with an op-amp as a preamp (as it has pre-in and out on the back of the receiver, so I can bypass any audio processing done by the receiver delivering a cleaner sound).
But this setup I am working with now is meant as a second room, that I wanted to get sounding close to my larger amp setup... and the 100w's def are not capable of driving 4 speakers to their potential as the 180w does. So I wanted to get something mid range ~130w.

BTW. Thanks for the quick response.
I have a lot of audio stuff here 8 pairs of high end speakers, and 14 receiver's.... and I repair a lot of electronics including speakers TV's receivers etc.

(Sadly for as many devices as I've successfully repaired I still lack the proper "key" that unlocks the 5 years of electronics classes I took, In fact I'm looking for a place to post a sort of "Q&A" to help me finally connect the dots in my mind. I have attempted to post a few places and all I get is "read a book" or "go to school"... or post removed "off topic" etc and so I am not sure where I can post this sort of "theoretical" questioning to ask people (who might think are unrelated questions), but have to do with the way I understand things in general).
Mooly: You might be interested in this :)

Read post #1 and post #2. There are test files in post #2. It would give you a good idea how much 'power' you really are looking at for the levels you want.

There is a large difference between "hearing the tones" and "feeling them"... it's a total other experience. Music so loud the mind cannot think of "other things" it must process the music only. I find if I listen at low volumes like most people do, I become unfocused on the music so easy and I start thinking about things I need to do or what I might post later etc. But when I pound the music it pulls my consciousness down to focus on this event only. And I can really "trip out" I get rushes and sometimes even pour tears out my eye's from the sheer joy this level of music brings. (And before you say "you'll damage your ears") it's not like that, I have a way of adjusting the shrill mid & treble out with the DAC's built in EQ, so that it almost sounds muffled at low volume. And now when I crank it there is no "it's too loud or too shrill" everything becomes balanced and equal and more than anything the music sounds "smoother" than any other setup I've ever heard.

I am extremely picky when it comes to audio and what sounds good. I went to pick up a pair of Paradigm Monitor 9's at this guy's house near me who has a massive McIntosh amp he had recently purchased, which he was driving these off. They sounded HORRIBLE! And he was saying "See these sound good right!?" as he turned it up more.... to me it sounded like a "cheap TV quality sound" amplified 100x's (seriously). Despite this I bought them off him anyways, set them up and I was a bit discouraged (since I normally use the larger boxes Monitor 9se MKIII's) until I sat down to adjust the EQ... then after a few tracks listening and tweaking - there it was like magic smooth and distortion free. I felt like calling the guy over to hear how to properly setup high end audio. But everyone has an opinion... and sadly, no one ever listens to mine.
I might add I also do not use tone generators etc to check my audio... I put music on and I listen... and if I hear any instrument that has a "tone" to it that is not natural I trim that tone on the EQ down until it sounds "real". I do this with each frequency until I take out all the "added tones" that the receiver, amp and or speakers introduce.

In fact recently I picked up a bunch of IEM's because I was getting so upset with the professional reviews using the strangest words to describe the sound of each IEM... I said these guy's have no clue and I purchased a bunch and well FLAT with no EQ they had massive sound differences. But I sat down and played them and adjusted the EQ for each one. In the end all of them are nearly identical sounding now (well ironically accept a pair of JVC's which no matter how low I dropped the Mid's and Treble it would not stop being too shrill to handle)
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Have you seen a hearing specialist, maybe you are deaf. Many deaf people don't know they are deaf. It could be that your speakers are stuffed and the voice coils prevent the cone from moving and now you have to push so much power just to get them moving.
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You can be glad you are not my neighbour, you would not have a window left in your house.
Actually I spent a lot of time testing my setup as to what the neighbours can hear. At night late when there is no cars and no birds etc I would play music at the levels I like. Then I'd go outside and see how far down the street can I hear it? And at what strength. I did this and found it reached the end of the street... I went back and I insulated my music rooms windows, and then I could only hear the music 3 houses over and at that it was hard to tell where the music was coming from. So I went back inside and I added a nice thick 3/4 inch MDF plywood board over the insulated window... when back outside and I could barely hear it from my neighbours yard (it was certainly not going to bother anyone at this level).
Have you seen a hearing specialist, maybe you are deaf. Many deaf people don't know they are deaf. It could be that your speakers are stuffed and the voice coils prevent the cone from moving and now you have to push so much power just to get them moving. Maybe you where one of those obnoxious children that got a tin drum for his birthday and just like to annoy everyone else.
I don't need to seek a specialist for testing my hearing, as I actually can hear tones others cannot when I've downloaded some hearing tone/tests. In fact some of them I listen to go to such a high tone that the compression algorithm cuts it off when I view it in an audio editor. But I was able to hear the entire tone all the way up until it reached a tone that would not make sense to even use in music. Like a old TV's high pitch.... you don't get hearing damage when the audio is clean and clear of distortion, you get hearing damage when it's distorting.

Really, everyone has an opinion yet never does anyone come to hear the way I run my music "loud" which is not like the traditional "loud".... I picked up a pair of speakers off this guy who was running them off a Yamaha receiver and he was like "See these are great!" and I thought to myself "how can you even hear the music behind all that distortion?" I never offer to adjust peoples stuff - because they will assume I'm an idiot and might blow their stuff up. Meantime, I dare anyone who thinks my "loud" is too much to actually hear it in person. (not that you could living afar)....
Oh well this is just another typical forum, you post for help and suggestions on "DIY" and all they do is drop a "don't DIY" or "it's possible but not worth it, so don't do it" then... oh then all the negative commenters come rolling in, just to run me down or mock me for no logical reason other than they enjoy it.

Great welcome.... this is site is looking like all the rest "come here to share build ideas" but instead people just hoard them.
It's so typical of online forums where people "know how" but never actually discuss "how to's" or sit down with you to say "hey I like your idea can I offer some help with the design?", but I guess that's because everyone hoards it for "profit"...

How is anyone going to learn if the teachers teach it wrong, and when you ask "what does it mean" they are like what do you mean? It means exactly E=R/I! But that's NOT what I mean... and when I ask in a way I need to hear it said to learn, all they do is argue "watch a video" "read some books" etc... but the problem with these all is the same - they never use these "arbitrary values" to actually affecting something real. So in my mind these "arbitray values" have no value and there for I do not store/memorize and it's lost. Sad because I spent 5 years taking electronics classes... and I still can't grasp the "concept" because it's never applied to "cause & effect".....they assume all you need to do is memorize the math and you'll know it (conceptually). No I need to know it (conceptually) before I can apply the math to a concept. I can't apply math to "no concept" and expect to understand a "concept"....

So ok, let's get on with the running me down further, until I am modded or banned, for whatever silly reason they see fitting.
Running you down was not my intention, writing a prose and then expecting a member, who by the way is not a teacher to respond to is silly. Remember none of us is sitting in front of your equipment and nobody experiences sound in the same way. What I can tell you as a fact that I did in my teens and twenties did what you are doing now, and I regretted it since my hearing got so F ed up from loud disco music that I have today at the age of 70 diverted completely to headphone and nearfield listening to be able to enjoy music. My advice is, shrink your listening space, move closer to your speakers, then turn the volume up so you will also eliminate the off wall bounce that is time delayed and smears the sound. Keeping in mind that doubling the distance from your speaker attenuates the spl at your listening position by 20 log (distance) If you want to blow off your ears, it is easy get a Crown (they sound good) and a very efficient speaker say around 90dB/Wm and you can produce loud sound in an amphitheatre. Your distance from your speaker is crucial for bot loudness and distortion, I can with decent headphones achieve 104 dB and it still sounds great and let me assure you that you are not crying the water is forced from your tear ducts. Nearfield listening, say a meter (mx 3 meter) away does not impede upon spaceial quality or width or depth or layering because ratios remain the same. My current desktop system is original Rogers LS3/5a and 1969 JLH
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It sounds like you are pushing this quite hard, maybe you are expecting to much :)
Well I've had some more time to figure out what is going on here. And it seems that all my other receivers and amps really move the woofers, so you "feel the music" but in this case of this receiver it's like it goes up in volume and up and up but the woofers barely move it's just sort of generating the tones that emulate a big sound but without actually moving air/woofers. So it's very lacking in punch/kick/power tho it is very clean sounding. Also, the heatsink with the fan on it, is as cool to the touch as the room is... so it's not a temp thing triggering it, it's got to be the voltage that it was set to....

And I think that is the source of the problem, they wanted to cheap out on manufacturing costs by using less metal in the heatsinks, so they had to set the trip limit lower since the heatsink was not thermally deisnged to disapate more heat than at that tested voltage level "as is". I mean it literally sounds like it can still go up in volume since it's not hitting that "it's begining to distort point".... and again all my other receivers and amps all go much louder and drive the woofers where this one is just starting to push them in and out when it cuts.
You ARE damaging your hearing...damaged hearing is a permanent affliction that cannot be fixed...I've said my piece, my conscience is clear. You've been warned by someone who knows.

You know I went on a long drive with a friend last year, I brought some tunes and I sat down and adjusted his bass/treble/faders etc on his deck. I began to pound out some tunes... he was "having fun" but then after almost the whole CD had played he was like "Dude do you have to listen to it this loud? Like my ears are hurting I'm afraid you are damaging my ears!" and I looked at him and I laughed I said "dude if there is no distortion then we are good." and he said BULL let me take out my Db reader (the one he uses at his work/factory to test Db's in areas that CAN cause hearing damage) to make sure his employees are not suffering hearing loss. And he took it out and we tested it and it said the levels were more than safe... so he said "no way!" and he shoved it right next to the speaker and it was still within a safe range. He was so sure I was damaging my ears too, yet the Db meter said otherwise... I tell you there is a differnce between it sounds smooth loud and clear and it's loud and irratating and or distorting.

Last year I had one one pair of earbuds... and I would crank up some tunes and think these are kinda quiet and yet when I'd take them off my ears were ringing... I said well these suck and I picked up a bunch of higher quality IEM's and they are much louder but they don't make my ears ring after... that is because they are not distorting. When there is synchronicity in harmony - your ear hairs flow with it, but when there is distortion they get all tangled up and damaged because they are tossed all around in unnatural ways.... "go with the flow" - again I've tested my hearing and I can tell when something is hurting my ears. I went to a rock concert 10 years ago it was distorting so bad I could not handle it I had to stuff tissue in my ears, (which took a lot of the distortion away) but everyone else left there hald deaf for the night all talking overly loud when we exited.
I have just gone back to the first post in this thread.
A pair of 4 ohm speakers have been connected to an amplifier that is clearly meant to have 8 ohm or 16 ohm speakers connected to it.
It would normally get hot and fail however the amplifier in question has overload protection and is shutting down as it should.
A pair of 8 or 16 ohm speakers need to be obtained if the amplifier is going to work correctly.
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As you know, that unit is only rated for 8 ohm speakers so expecting it to run a 4 ohm load at high volume is unrealisitc, regardless of how other brands or units may handle the same load.
And if you really want to find out what it can, or cannot do, you need to be able to reliably measure the output power.
For that you need a signal generator, a scope and a 2 channel 8 ohm resistive audio load.
Given the unit is about 20 years old it's also possible it's simply not performing to spec.
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