Let us use a bit of logic to resolve this... I have an Axiom but it would be a lot of screws to take out to get to the part... so let us think about this. The resistor value starts with a "1" and we know it is 5% tolerance (gold). we know the resistor burnt up with likely 5 volts on it... Value could be 1000 ohms, however the voltages present (12 volts max) would NOT have burned up a resistor of 1000 ohms. The USB area is mostly 5 volts and across 100 ohms is only a quarter watt... not enough to really burn up a resistor... First thing is to MEASURE that the resistor s open... in spite of being burned, it MAY still be OK... these resistors now usually either open or remain close to their value. The resistor ALSO may be a fusible resistor intended to act as a fuse... Is the resistor open or not? is it near a resistance with a "1" as the first digit? If it is not open I suspect it is not all of the problem. In that case, look for a burned circuit trace on the board. If it is open, then MEASURE the voltage across the resistor with the power applied. If you find 5 volts, then it MIGHT be a 10 ohm used to limit the USB current to 500ma. Get back to me with your findings... I have unraveled many of these things...
Testimonial: "Hi Fredy2, thanks for your assistance in helping me isolate the problem! Cheers, Rock "
Here's more detail. M-audio Axiom 61 gen 1. Need schematic for power/ I/O pcb. R1 is burnt so, a.) I don't know the value and, b.) I don't know what caused it. The previous owner said the USB was flakey but the Midi was OK. I suppose he was using a AC/DC adapter so I found a 12VDC @ 300ma adapter and plugged it in and it turned on but I smelled something burning. At this point the unit seemed to work OK and I tested the controls and display, seemed OK but I did not have the Midi connected to anything.
Upon inspecting the PCB, the USB connector solder joints were fractured so I re-flowed them. One pad lifted (from the back, pin 1, ground?) so I bridged that with a tiny piece of wire. This seems unrelated to the R1 burning but is in the same area so it's suspicious.
When I plugged it back in, no display and the R1 still overheating. Burnt R1 measured 2.4 ohms after the first time I powered it up, and now measures 5 ohms. There is about 3 volts across the resistor. The resistor appears to be ¼ watt or less so no wonder it’s burning up. Oh, and the resistor color and was RED when I removed it and looked at the back of it. I am not very good at this without a schematic so it it comes down to it, I’ll probably just draw one up. I’ve got an email out to Maudio but I’m not hopeful they will be of any help.
Thanks in advance.
The M-Audio Axiom reequires a 12 VDC CENTER POSITIVE 1000 ma adapter. Check your polarity!!!!!!! MANY of the adapters are negative on the center but the MAudio requires positive as per the markings. I have an aXIOM 61 AND two M88 M-Audio keyboard controllers. Let me know if your adapter might have been backwards as it would certainly cause the problem. I am still lookng for a schematic. I SUSPECT that M-Audio has a polarity protection diode that would short the supply to ground... if so, the resistor is probably involved with the power input... also the LOW number "R1" would indicate that it is near the input. If AC was applied to this the input bypass electrolytic is likely shorted and MAYBE the input regulator, probably a 7805 may be blown... Keep me posted...
The TO220 is probably a 7805 regulator. See if there is a diode in the area where the power comes in. That is the problem of those "universal" adapters... the ones for small currents tend to swing way above the design voltage, even with a load. While I would probably not use one that went that high, that is not likely to be the problem at hand. We need to go into trouble shooting mode. This means to apply a current limited source of power and trace the input. I suspect you would find the 12 volt source goes through that burning resistor to the TO220 regulator chip... see if it has nomenclature like VR1 which would flag it as a regulator for sure. I might expect they would have a 1N400x diode to prevent reverse voltage to ground. Take a 100 ohm power resistor in series with the supply and apply that to the input and using the meter see where it is shorted. The TO220 PROBABLY has the part number on it... some lately are SO dim you need a bright light to read that they aare even there.
Glad to hear that it is working... Use of the poly cap in that function is NOT recommended as they have more inductance that does not provide as good performance as a high frequency bypass. On the resistance values, 2.4 is a standard and 2.0 and 2.7 are standard values. 2.4 is less common than the other two but should not be critical anyway. The resistor is probably intended as a prefilter with that electrolytic and the ceramic cap. I suspect it also is to act a fuse... there are fusible resistors, however when they go the open completely so this one is not a fusible... often they use FRx as the nomenclature for those anyway. Since this took a hit and the ceramic fried, keep in the back of your mind that the electrolytic may go and even the regulator chip may have degraded a bit... if it happens you will know right where to go.
In the end, this Axiom 61 really had several problems. 1.) When I first got it, I noticed something loose inside, it was a copper penny. What havoc might this have caused? 2.) There was evidence of a "Coke Spill", I've seen this before. Completely disassembled the key contact board and cleaned up all the mess. Luckily, no Coke got between the rubber contacts and the pcb, just a lot of goo on the keys, boards etc. 3.)The USB connector had fractured/sold solder joints and one lifted pcb pad to be repaired. "Falkey USB" was the only problem reported by the seller. 4.) R1 burning up which sent me on a search for a schematic which brought me here. Was this unit worth the 25 bucks I paid for it? Time will tell.
Twenty five would be a fair price given the problem... The first thing on a liquid spill is to remoove the power as the electrolysis quickly eats through circuit traces. Always use DE IONIZED water to clean soft drink spills. The circuit boards are cleaned with de-ionized water after they are soldered during manufacturing. There are some components that are not sealded and those cannot tolerate water. For sliding faders use CRC226 available at Home Depot in the electrical dept. NEVER use Deoxit or Blue Shower in pots... it destroys the lube. My Axiom I got for about 25% of the street price from Musicians Friend as a condition 5 "Parts Only" unit. One fader was smashed... $1.50 replacement and a cable had been knocked off... wasn't very challenging at all... I am currenlty working on two Behringer 205D personal monitors. One has a fried 4580 op amp that is surface mounted and that may be the only trouble. I do have a pair of those "Smart Tweezers" for testing components... they are very expensive but they do work reasonably well.
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I had the same problem with my Axiom 61. I didn't find any information on the internet about resistor R1. Studying the circuit I discovered that it is only a protection resistor between the output of the 5v supply and the rest of the motherboard circuit. In my case what caused the burnt was the C3 capacitor (470uF 16v) was in dead circuit, grounding the source output and stopping the energy supply for the rest of the board. I changed the capacitor and put a low value resistor (6.8R 1/4w) and the controller returned to work perfectly.
(I don't know what the original value of the R1 resistor was, this resistor I used was what I had available at home. I don't know what the effects of this replacement were for the controller to work. I'm just sharing what worked for me.)
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Thanks for keeping up with me. I checked the manual and it says 12V DC, 250mA-300mA, Center positive. I'm using a unit labeled 300mA but I'm skeptical because the output measures 17-18 VDC even when loaded with a 470 ohm resistor and filtered with a 3300 uF cap. (also confirmed this on the scope for ripple) hmmm, a little high me thinks. But I don't think that's the problem because I get similar internal voltage readings using only a 9V DC adapter??? so it seems the Regulator ( the device is unmarked in the unit but is a TO-220 package) apparently is doing it's job but I'll look for a 12 volt unit that actually gets closer to the 12 volts specified. Yes, there is a polarity diode in the ckt.
OK, so I guess the only way to solve this is/was to roll up our sleeves and dig in and trace to see what goes where. After a little hunting around and flipping the board back and forth... cut to the chase...I unsoldered two caps (one by accident) C3, my target the 470 16v and C2 the happy accident a .1 ceramic. A year ago, I picked up a Cap meter from Part Express and this is the first time it has identified a bad cap (I other wise might not have identified) the .1uF SLOWLY increased in value as I kept it connected to the meter. This indicated the cap was/is leakey. Bingo. I put new caps in both locations and PROBLEM SOLVED. So you were very close at one point you suggested a lytic although this one is downstream of the regulator and it was not the lytic but the .1 ceramic disc parallel with it. BTW, I replaced the ceramic with a 100V poly S/B fine AND I decided the resistor value originally was 2.4 ohms since that is what I originally read and it seems fine. Still, sure would be nice to have the comics: ) (ya know, skizzies)
Cheers,
Rock
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