its in a samick smp-4000 ..its driving me nuts .. 3 resistors lifted and q117 still affects drivers bases when i freeze it .. cant get it bias .. positive to negative swings with heat and cold ... am missing something obvious here .i am going to pull r159 to see what happens ..if that dont work ic101 is going . ... its very odd as good channel only works with bad channel removed although bias is still ok on that channel ... https://elektrotanya.com/samick_smp-.../download.html
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Re: can anyone explain how this protect circuit operates ?
Does Q117 actually have anything to do with bias? Or is it just for driving the protection LED?"Tantalum for the brave, Solid Aluminium for the wise, Wet Electrolytic for the adventurous"
-David VanHorn -
Re: can anyone explain how this protect circuit operates ?
Well... from what I can make out from it:
The output from the protection IC, IC101 provides feedback to Q120 via R108(?), and by extension, Q101/Q102. That seems logical enough. Normally that IC101 (TA7317P) is designed to switch a speaker output relay, but they seem to be using it to switch off Q120 and thus cut power to Q101/Q102 in the event of a fault instead. So it would seem that this would effectively disconnect the audio input signal to the amplifier, and that's about it.
That output from IC101 also drives Q117 through the voltage divider of R159 and R160, lighting the protection LED (LED 2) if there is a fault.
I'm thinking that C123 is probably used to prevent LED 2 from flickering, and Q118 simply used to provide a faster way to discharge C123, but keeping the discharge current low enough that in an actual fault condition, LED 2 will still be able to light. Seems a bit overcomplicated but that's all I can think of as to its purpose.
The next stage of that circuit with C124, Q119, I think may only come into play at switch on\off, as it has a larger capacitor, and probably again, to prevent some spurious LED 2 output at power up or power down.
I really see no way that Q117 could affect the actual amplifier stage, unless you're accidentally freezing\heating IC101 and\or one of its support components."Tantalum for the brave, Solid Aluminium for the wise, Wet Electrolytic for the adventurous"
-David VanHornComment
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Re: can anyone explain how this protect circuit operates ?
at present i have r142 and r155 lifted and cooling and heating isnt changing voltages at the drivers bases like it was before .so at least its now stable but no bias drive .. i went over all resistors in circuit and transistors and nothing jumped out as yet .Comment
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Re: can anyone explain how this protect circuit operates ?
case closed for now .. found broken trace by q107 collector .previous work is shoddy .. bias will turn up now . still work to do yet but it looks like its going to work ..Comment
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Hi friends of electronics
What you see in the video and pictures attached is the circuit for charging the batteries of a DC motor.
The problem is that this circuit cannot charge the batteries (3 1800mAH NiMH batteries) any more. When the circuit was OK, its green LEDs lit up one at a time to show that the batteries have charged more. But now that the circuit is flawed, LEDs light up as you see in the video and at the same time successive beeps are heard.
Please help me fix this circuit.
(the datasheet of the IC: https://pdf.datasheet.live/28... -
Hello,
I know some might say... just buy another one. Sell it as parts..!
So had this AMP for quite some time. Recently I saw light smoke coming out of the AMP. Had my fire extinguisher close by. Just kidding. Turned immediately all devices off from mains.
Let things cool a bit, and opened up the amp device. I clearly saw on the main board which hosts the 5X amp (5.1), 3 10 ohms 1W resistors had their leads looking black, while the rest of the remaining 2 x 10 ohms were brownish as being installed from factory.
Spent some time downloading the Service...06-11-2024, 08:38 AM -
Hello friends,
Looking for some guidance here. The RAM voltage circuit on this motherboard keeps burning out PU301 which is a RT8231AGQW. Copy of the board with the burnt chip attached with some voltage measurements and copy of the schematics also included.
I think I've checked almost every component in the circuit, but when I change the RT8231, the laptop starts I have 1.2V on the inductor for about 10 seconds and then the RT8231 goes south and no more voltage on the inductor. All other voltages on the laptop are good, this is the only one conking out for a reason I... -
Hello.
I have seen a short circuit tester made with 3 * 9V batteries, a voltage limiter component and a resistor connected to the probes of a multimeter.
The theory is that the meter becomes sensitive enough to read very low resistances and the lowest resistance to ground on a circuit is likely to be a short circuit in that area.
Link
The Amazing $1 Short Finder Upgraded! Convert ... - YouTube
https://www.youtube.com/watch?v=0eixDdCpiO4
My multimeter isn't normally sensitive to very small resistance, but when I put a 1 mega ohm resistor... -
Hello. MSI B250 Gaming M3 board, short-circuit on the power supply. Found a problematic mosfet VQ1
(N-PK616BA_PDFN8-HF) soldered it out - short circuit is gone. I replaced VQ1 + VQ5 (N-PK632BA_PDFN8-HF). VQ1 was replaced with PK618. After starting attempt VQ1 is lit again. What can be the problem? In the driver?
Schematic and Boardview here
...04-04-2025, 03:57 PM
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