Otari MX5050 8 track repro popping/crackling

  • Thread starter Thread starter 999imw
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999imw said:
I demaged yesterday.... unless the demag device didn't work properly. It seems kind of old but I could hear it humming. Would magnetization cause this sort of problem? I thought that mainly affected the high frequencies....
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Honestly don't know, I'm inexperienced compared to many of the guys in here.
 
We just scoped the machine. We did a sweep with a tone genrerator from 40hz to 2khz and the the frequency of the popping seemed to follow the frequency of the tone. It's the same on all channels and its only while playing back or monitoring repro during recording. You can't hear it while monitoring the input. Could it be a problem with a head? It sounds the same while listening back off the record head though.... not sure what my next step should be.
 
not the heads. Your problem is in the repro circuit. It can be a physical unstable connection, like a connector or solder in the PCB. anything in the circuit path. Does it happen in all channels ? or only on certain ones ? if in all, it is something that is common to all channels, like the power supply for example, did you probe VCC with the scope to check if the noise is present on the power supply lines ? you need to follow the audio path with the scope and find out where the noise starts to appear. However i would check the power supply first, to see if the noise is there.
 
We took the machine apart trying to find one common section of the circuit that all channels had to pass through. We found the wires that lead straight from the heads to each individual channel card and all the connections look clean. The unit is in pristine condition. If i's the power supply, wouldn't I hear this while monitoring the input as well?
 
try putting the machine on PLAY and monitor the input. The noise may happen only when there is more load on the power supply, like when the motors are running for example. See if the noise is in there. Is the noise present in all 8 channels or only in some ? you may think that the unit is in pristine condition, but cracked solder joints are almost impossible to see by the naked eye. It can also be an IC or capacitors, which you can't see if they have issues with the naked eye either. It is important to know if the noise is in all channels or not, check that, and the power supply, it is a simple check. Put the scope in AC mode, probably in the 100mV vertical scale and watch for the noise as well. If you answer these two questions it will be easier to continue debugging knowing this information.
 
There is no popping while monitoring input with the machine playing. It's only on playback or while monitoring repro during recording. It's as if its on the tape... I guess it could be a capacitor or IC but the sound is coming from all 8 channels so it would have to be the exact same problem in each track..... Still need to test the power supply. I'll do this next time friend brings his scope over. I guess we decided that if it was a power supply issue the noise would be present while monitoring input also.
 
999imw said:
I demaged yesterday.... unless the demag device didn't work properly. It seems kind of old but I could hear it humming. Would magnetization cause this sort of problem? I thought that mainly affected the high frequencies....
Click to expand...

I would visit this again, I have had static noise on tape caused by a lack of de-maging. Have you done this before and know how to do it? Did you do all the guides and rollers as well?

I found this so have a read. It points out the de-mag dangers.

Alan.
 
999imw said:
There is no popping while monitoring input with the machine playing. It's only on playback or while monitoring repro during recording. It's as if its on the tape... I guess it could be a capacitor or IC but the sound is coming from all 8 channels so it would have to be the exact same problem in each track..... Still need to test the power supply. I'll do this next time friend brings his scope over. I guess we decided that if it was a power supply issue the noise would be present while monitoring input also.
Click to expand...

if it is present on all channels. it has to be related to a common component. The power supply may have a different load when in input mode or play mode. Do the following tests to check if the noise is present on the following scenarios:

1. Put it in input mode, but with the reels moving - either play if you can or FF/REW. Check if the noise is present
2. Keep it in play mode but with no tape, move the lifters to avoid a stop. THe reels will spin fast. Is the noise present ?

When you measure the power supply with the scope, you want probe it from one of the opamps in the repro circuit. THe noise may be present only in certain areas of the power distribution (for example not present in the power supply PCB, but present in the repro PCB)
 
witzendoz said:
I would visit this again, I have had static noise on tape caused by a lack of de-maging. Have you done this before and know how to do it? Did you do all the guides and rollers as well?

I found this so have a read. It points out the de-mag dangers.

Alan.
Click to expand...

This was the first time I've ever demaged a tape machine but I followed instructions I found online. I went over all the metal parts in the tape path. The demag wand I'm using is a Realistic model 231X . It looks to be pretty old.... Is there a way I can test this to make sure it's functioning properly? After reading that article I'm wondering if it's powerful enough....
 
if the parts are magnetized, you will get dull frequency response mostly. Random noises like crackling are not because of magnetization.
 
Yeah I think we've safely ruled out the heads. Demagging is probably a waste of time.

You're listening from the XLR out from each channel correct? Not the headphone jack? If so, then it is either the power supply at fault, or some sort of circuit that each channel goes through before its respective XLR. I think power supply is the most likely candidate. There are some substantial caps in there that could probably use replacing, whether they are failed or not it's a good idea, since they will dry out and fail sooner or later.
 
I hear it coming off both, the xlr outputs and the headphone jack....
 
is there a link somewhere to look at these schematics ?

also, did you used de-oxit on all potentiometers to clean them up ?
 
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