| mike49504 |
| im working on this amp and the inputs do not work and only 1 rca output works just wondering what i might check or could it be the preamp drivers |
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| sdoom |
Hi
sometimes the RCA jack itself is not ok, best thing is to check the power supply voltages across the op-amps (usually +15 and -15V). Usually pre-amp section faults are easy to find if you feed a small sine signal to the RCA inputs and trace the signal with a scope. |
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| mike49504 |
| just wondering if anyone knows if the i think lm361n ic chip controls the outputs theres another ic chip right next to it but cant tell the numbers because someone sratched them off dont know if the factory does that so u gotta send it back for repair |
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| Perry Babin |
I can't believe they didn't deface that IC.
That IC accepts the triangle and audio waveforms and generates the PWM output. If you have audio (it could be shifted or straight DC if the feedback circuit is working properly) on one input and the triangle waveform on the other input and DC offset on the output, it's likely that the IC is defective. Generally, when they fail, both outputs of the IC swing the same direction (both go high or both go low). That's not possible if the IC is in proper working order.
If it's like some of the other amps that use that IC, there are unused pins. The unused pins have solder pads that lift easily when heated. To prevent damage to the board/pads, use chip-quik solder (desoldering system). It's relatively expensive but you don't need much. chip-quik will send you a sample for free. Digi-key sells it when the sample runs out.
http://www.chipquik.com/ |
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| mike49504 |
| thanks perry i will check that ic out the lm361n do you know if thats the only chip that controls the outputs or does that other ic control them also if so do u know the number of that chip because the defaced it so i have no clue what part number it is |
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| Perry Babin |
For amps that use those ICs, the IC next to the blue crystal generates the carrier wave (square wave ~80kHz).
There is an op-amp that takes the square wave and converts it to a triangle wave (op-amp used as an integrator).
There is another op-amp that compares the output to the preamp signal and corrrects for errors (simple servo/feedback circuit).
These op-amps may be on the same IC or on different ICs. It varies by amp.
The triangle waveform and the audio drive waveform (out of the op-amp being used for error correction/feedback) are driven into the lm361 (could also be an NE529). The 361 drives the outputs through a driver stage.
If you post the voltages on all of the pins of the lm361, it will help in troubleshooting. |
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| mike49504 |
| well kinda hard now to i was testing the voltage on the pins of the lm361 and i touched one of the pins with my meter probe and well the power supply decided to take a **** on me it poped a trace from the remote wire to the diode took out the diode and i fixed the trace and the diode but now the amp is in protection |
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| Perry Babin |
How did you blow a diode in the remote turn-on circuit (this may help in troubleshooting)? That's nowhere near the 361 in most amps. Were you probing the 361 when it the damage occured?
Whenever testing an amp, you should always use an inline current limiter (resistor or headlamp if your supply doesn't have current limiting) or a fuse rated no higher than 10 amps. These won't always provide complete protection but they will save many components from damage when something goes wrong.
Since I don't have any notes on a 1500, you may need to post some photos (better than those on ampguts).
justonemoreamp may have a schematic to help you troubleshoot the protection circuit if it was damaged. |
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| mike49504 |
| just wondering how i might get the amp back out of protection mode?? |
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| Perry Babin |
| I asked questions that may have helped diagnose the problem. They were not there because I like to type. :) |
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| mike49504 |
| sorry perry it was a long day ok for starters i had a friend helping me out on that amp and writing down the voltage on thoose pins of the lm361 well i finally got it out of him he said with the neg lead of the meter he had it on the ground terminal of the amp and he touched the diode with the pos lead with the amp powerd on thats when it took out the diode so i was like whatever but the amp itself whent into protection before that he said he put on lead on the emitter of a transistor in the power supply and the other on a collector of the same transistor and heard they relay click inside the amp and right then it went into protection mode so now not sure where i go from there i was working on the colossus amp at the time thats why i had him help me well guess i shouldnt have now i have more problems wrong with the amp |
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| Perry Babin |
Since I have no experience with the amp, no schematic and no photos, I can't help much.
If he burned a trace, he likely shorted two pins together. You need to check the components in the area where he was probing the circuit. check the transistors for opens and shorts.
You need to determine if the supply is operating. If you have rail ±rail on the source of the outputs, the supply is operating.
If the power supply is in operation, the amp may be OK other than the protection circuit. |
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| mike49504 |
| perry to me you are a god i wanna thank u very much for telling me what to check i replaced 2 transistors in the protection circuit and amp is not in protection anymore now i gotta figure out the rca inputs im gonna check the lm361 like u said to see if its bad the is a transistor in the output side right next to the lm361 the number on it is 431a when i check it in circuit from collecter to emmiter it says its shorted when outta circut reads good and when its outta circuit i touch my meter leads on the board where it goes and from emmiter to collecter it says its shorted wondering if this is normal or if it will read like that if that lm361 is bad? |
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| Perry Babin |
There has been a problem on some amps of similar design where some surface mount tantalum caps short. Check all black 2 terminal SMD devices in the area. They will have board designations Cxxx. If you find any shorted, lift them and check them off of the board. They may also leak (electrically) instead of being shorted to zero ohms so sometimes they are difficult to find.
The tantalums can be somewhat sensitive to high temps so turn your iron down a bit (if it's temp controlled) if you have to remove them. It's better to replace them if you remove them but some people reuse them with no problems.
Do the transistors have any other markings like DF or 3B? |
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| mike49504 |
| all the numbers on the transistor is kia 431a 409 |
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| Eva |
| That's actually a TL431 IC, a shunt voltage regulator similar to an "active" zener. |
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| mike49504 |
| the kia 431a is a transistor 3 pins just woindering if the lm361n cross's to anything or do i have to order that exact part number?? |
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| Perry Babin |
The 431 could well be a shunt reg. That design uses a regulator set ~12 volts off of the rails for the drivers. Most use zener regs but this one could be different.
Before I found any information on the IC (all were defaced), I used input, output, power and ground connections to determine that an NE529 was a good sub. I've used several in kicker amps. Of course, it's always best to use the exact replacement. |
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| mike49504 |
| i replaced the lm361n and the amp does the same thing no output theres another ic chip next to the lm361n but its defaced all i know is it has 8 pins per side wondering if someone could tell me what part number that may be or what else to check to see what the problem may be |
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| Perry Babin |
Pin 4 of the 361 should have a triangle waveform of ~4v p-p and ~82kHz.
Do you have that? |
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| mike49504 |
| hi sorry i dont have a scope yet really wishi did im thinking the other ic has failed due to resistors heating up in the output side of the amp right next to the coils i dont know if the tl494cn ic has anything to do with the output since the amp comes on and stays on so im thiking the other ic has failed its an 8 pin ic next to the lm361n because when u hook up speakers to the amp i can hear a engine noise type thing on the outputs when tested on the bench which i think im hearing the op amp or preamp drivers working and i looked at the traces on the board where the come off that ic with no number on it and the resistors are inline with that ic |
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| Perry Babin |
Did you ever get around to measuring the DC voltage on all of the pins of the 361?
Black lead on the ground terminal of the 361. Follow the trace away from the IC to find a point where you can easily touch your probe (where there is less of a chance of shorting to adjacent components).
Post a list instead a long line of text. Look up the datasheet if you don't know the pin layout (don't guess).
Pin 1:
Pin 2:
Pin 3:
Pin 4:
Pin 5:
Pin 6:
Pin 7:
Pin .....
It's time to buy a scope. Email me links to any that you're thinking about buying and I'll try to point you in the right direction. |
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| mike49504 |
lm361n
PIN1= 12.1
PIN2= 0
PIN3= .20
PIN4= .20
PIN5= .06
PIN6= 12.82
PIN7= 0
PIN8= 2.70
PIN9= .53
PIN10= 2.27
PIN11= .46
PIN12= 0
PIN13= 2.75
PIN14= 2.76 |
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| Perry Babin |
Those voltages are close to what I'd expect to see (except for the missing negative signs for several pins).
When you drive a signal into the amp, is there any output?
Does the relay engage after the delay?
If you measure the DC voltage on the speaker terminals (one lead on a positive terminal, one lead on a negative terminal), how much DC is there? |
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| mike49504 |
| the relay does kick on after the delay dc voltage on speker outputs is none and and when u drive a signal into it theres no output what so ever |
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| Perry Babin |
| Without a scope, it's difficult to know what signals are present/absent and where the signals stop. |
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| Perry Babin |
| Is there a master/slave switch on that amp? |
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| mike49504 |
| yeah theres a master slave switch on the amp but in either posistion still same thing no output |
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| mike49504 |
| hi just wondering if someone might be able to tell me where the op amps are located on this amp they are tl072cp but theres about 10 of them on the board theres 2 cards that stand up in the amp 1 for sub 1 and another for sub 2 theres 2 tlo72's on each board and on the main board theres like 7 or 8 of them wondering which ones i should replace to see if thats the problem with the amp since i have a alot of thoose tlo72's just laying around |
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| Perry Babin |
You can buy/make a cheap low level (preamp) signal tracer by buying a Radio Shack Mini-Amp (277-1008) and the cables to fit the input.
You can generally check op-amps with a voltmeter. If the voltage on the inputs (inverting and non-inverting inputs, not power supply inputs) match (for each op-amp in the physical package) AND the op-amp has the proper supply voltage, the op-amp is usually OK. If the voltage on the op-amp's inputs don't match and the op-amp is being used only for local signals (virtually all preamp use) and is not part of a larger servo loop, the op-amp is typically defective (or there's a broken connection in the local feedback loop). There's no reason to start changing op-amps for no reason. If you learn how to check them now, you'll save yourself a lot of time in the future. |
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| mike49504 |
| i replaced 1 opamp that was no good and traced the problem down to the ic chipset it has 8 pins wondering if anyone knows what part number that is or a good replacment part all i need is that ic and amp should be good to go |
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