flyingace
Active member
@sweetbeats,
My multimeter is Craftsman Model #82139
My multimeter is Craftsman Model #82139
flyingace
Active member
Thanks for the video, I did those measurements. 1-3 ohms on all the ones you spec'd. Did the plug to each, 0 continuity. Did the plugged in measurements and they came out roughly what you said, 36V blue, 51V red, 11V orange, 40V yellow.
sweetbeats
Reel deep thoughts...
That all sounds good. It’s not the transformer. So there is a problem with either rectification, filtration or regulation, or some combination thereof, on one or more of your regulated DC power rails, and aside from just starting to shotgun parts you really need to put a scope on it and actually see what’s going on starting at the output of the bridge rectifier…and I’d focus on the +15V rail for starters.
flyingace
Active member
It will be a few weeks before I can get up to my tech (2 hours away) and it might be a little while before he can look at it.
I spoke with another tech that specializes in mixers/sound systems up in branson, mo area. He is also the closest Roland warranty repair person and worked on one of my synths. He suggested two things: 1. test the VAC with the red to the pin and black to ground instead of the common pin. 2. set the range on my multimeter to a 2 decimal setting. There I got 0VAC from +15 and +18. All other voltages spec out to your list, so he suggested that if the unit wasn't blowing the fuse when powered on, that I should give it a try under load to the console. The M-520 works, all audio fine, no noise, super low noise floor as before.
Now the question will be will it blow the fuses again, was a spike while turning it on? Was running and turning the unit on via my furman power condition creating a spike and should I be powering the power supply on/off using the front panel switch from now on, after turning the power conditioner on? Should I just leave it on as @RFR mentioned? I know that analog studio in Nashville, Welcome to 1979, said he never turns his MCI console off, thinks it's better for the circuitry. I have plenty of air flow where my power supply is mounted.
I'll report back if it blows those fuses again and next chance I get I'll have my tech use his scope to check it out thoroughly!
I spoke with another tech that specializes in mixers/sound systems up in branson, mo area. He is also the closest Roland warranty repair person and worked on one of my synths. He suggested two things: 1. test the VAC with the red to the pin and black to ground instead of the common pin. 2. set the range on my multimeter to a 2 decimal setting. There I got 0VAC from +15 and +18. All other voltages spec out to your list, so he suggested that if the unit wasn't blowing the fuse when powered on, that I should give it a try under load to the console. The M-520 works, all audio fine, no noise, super low noise floor as before.
Now the question will be will it blow the fuses again, was a spike while turning it on? Was running and turning the unit on via my furman power condition creating a spike and should I be powering the power supply on/off using the front panel switch from now on, after turning the power conditioner on? Should I just leave it on as @RFR mentioned? I know that analog studio in Nashville, Welcome to 1979, said he never turns his MCI console off, thinks it's better for the circuitry. I have plenty of air flow where my power supply is mounted.
I'll report back if it blows those fuses again and next chance I get I'll have my tech use his scope to check it out thoroughly!
sweetbeats
Reel deep thoughts...
Great! Glad it’s working!
Switching power on at your power distribution unit is no different than switching it on at your power supply. You can’t create a surge by turning something on. I don’t think that has anything to do with whatever caused the fuses to blow.
Regarding bullet point #1: what did your tech mean by “black to ground”? The COM probe to the chassis? If that’s what they meant I don’t agree with that unless you know the 0V or “ground” reference for the power supply output you’re measuring is bonded to the chassis. It should be, but it’s not always. Sometimes the “float”, and you have to reference the 0V conductor for the power supply which is, in the case of the +/-15V supply of the PS-520 on pins 8 & 9. They ideal way external power supplies like the PS-520 should be wired, as far as the grounding goes: three-prong power cable comes into PSU chassis…ground conductor is positively bonded to PSU chassis as close to where the cable enters the chassis as possible. All 0V references for each regulated unipolar or bipolar DC power supply should stay separate and not bond to the PSU chassis (yet), but propagate separately to the console chassis through the umbilical. Then, all 0V references should positively bond to a common point of the console chassis as close as possible to where the umbilical enters the chassis. Then, assuming all metal members of the console chassis or positively bonded together (this goes for the PSU chassis as well), signal and power grounds as well as shields also bond to the chassis in the most reasonable direct way as possible with only one path each…everything is tied together using the chassis…then the console chassis and PSU chassis should be positively bonded together via the (ideally) braided shield of the power supply umbilical. Again, this is ideal state. The M-520 deviates from this substantially. And now you make me want to look at really old pictures of work I did to correct all this on my prototype console, which was a prototype for the M-50/M-500 consoles…and I currently use a modified PS-520 to power it. And had to correct stuff in it. Teac is not alone in these discrepancies. But it becomes a problem when a device is inconsistent with itself as far as the ground scheme. Then we really get into trouble either with noise interference or worse yet safety. Both were the case with my Soundtracs MX console…a grounding abomination. The M-520 isn’t bad, just not ideal. And, IIRC, there is some inconsistency with how and where the different regulated SC rails’ 0V references bond to the chassis, either the console or PSU, and how the two bind together. So the most accurate and reliable way to measure the output of a power supply is to measure use the supply’s 0V reference. Unless you verify the 0V reference is correctly bonded to the chassis.
Switching power on at your power distribution unit is no different than switching it on at your power supply. You can’t create a surge by turning something on. I don’t think that has anything to do with whatever caused the fuses to blow.
Regarding bullet point #1: what did your tech mean by “black to ground”? The COM probe to the chassis? If that’s what they meant I don’t agree with that unless you know the 0V or “ground” reference for the power supply output you’re measuring is bonded to the chassis. It should be, but it’s not always. Sometimes the “float”, and you have to reference the 0V conductor for the power supply which is, in the case of the +/-15V supply of the PS-520 on pins 8 & 9. They ideal way external power supplies like the PS-520 should be wired, as far as the grounding goes: three-prong power cable comes into PSU chassis…ground conductor is positively bonded to PSU chassis as close to where the cable enters the chassis as possible. All 0V references for each regulated unipolar or bipolar DC power supply should stay separate and not bond to the PSU chassis (yet), but propagate separately to the console chassis through the umbilical. Then, all 0V references should positively bond to a common point of the console chassis as close as possible to where the umbilical enters the chassis. Then, assuming all metal members of the console chassis or positively bonded together (this goes for the PSU chassis as well), signal and power grounds as well as shields also bond to the chassis in the most reasonable direct way as possible with only one path each…everything is tied together using the chassis…then the console chassis and PSU chassis should be positively bonded together via the (ideally) braided shield of the power supply umbilical. Again, this is ideal state. The M-520 deviates from this substantially. And now you make me want to look at really old pictures of work I did to correct all this on my prototype console, which was a prototype for the M-50/M-500 consoles…and I currently use a modified PS-520 to power it. And had to correct stuff in it. Teac is not alone in these discrepancies. But it becomes a problem when a device is inconsistent with itself as far as the ground scheme. Then we really get into trouble either with noise interference or worse yet safety. Both were the case with my Soundtracs MX console…a grounding abomination. The M-520 isn’t bad, just not ideal. And, IIRC, there is some inconsistency with how and where the different regulated SC rails’ 0V references bond to the chassis, either the console or PSU, and how the two bind together. So the most accurate and reliable way to measure the output of a power supply is to measure use the supply’s 0V reference. Unless you verify the 0V reference is correctly bonded to the chassis.
flyingace
Active member
I trust you and your immense knowledge of all things Tascam for sure! I have been extremely lucky with my M-520 and PS-520 as well as my MS-16. The previous owner took good care of them. He is 91 this year and I have not spoken to him in 2 years to know more about what maintenance was done over the years. From what I understood, it was lightly used from ‘86 - ‘89, put in storage until 2001, serviced (which he said needed practically nothing but cleaning), then in storage until 2021 when I bought it. Other than some scratchy trim pots, I’ve not had to do much else except reconnect the headphone jack and (thanks to you) fix the master VUs (turns out it was operator error when fixing the jack, a tiny plug got unplugged on the master/buss panels).
I appreciate you very much, thank you, thank you, thank you! I’ll keep you posted as I use it and if it happens again, I’ll do the safe thing and get it fully checked out.
P.S. I’m buying a scope and learning to use it, thanks to my tech friend, who is going to train me.
I appreciate you very much, thank you, thank you, thank you! I’ll keep you posted as I use it and if it happens again, I’ll do the safe thing and get it fully checked out.
P.S. I’m buying a scope and learning to use it, thanks to my tech friend, who is going to train me.
flyingace
Active member
So far so good, no issues as of yet (hope I don’t jinx it!). I used the console from Wednesday to last night, multiple channels, multiple busses, Aux effects, etc. All seems well. I hope it stays that way for a while before needing any major repairs. Thanks again for all your help @sweetbeats, I feel like I know my console even better now and a little less mystified for the future.
sweetbeats
Reel deep thoughts...
Your audio power rails were down. They are back up, and so I would expect all audio systems to be functioning. I’m glad it’s working. Something happened and the fuses did their job. 
flyingace
Active member
Yes, they did their job!! Honestly, I had no idea how much weight the power supply pulls, not just electricity but channeling it into so many different voltages and the protections… Super happy that I own this mixer, it sounds amazing and I was really sad thinking I’d have to move on from it. Not to sound too pedantic about it, but with vintage gear, and some components “unobtanium” these days, let alone, finding anyone near me that could work on it… makes me worry about it’s demise one day.
sweetbeats
Reel deep thoughts...
I don’t think there’s anything unobtanium in an M-500 series console as far as electronic components. And because the service manual with schematics and parts lists is readily available and everything is through-hole construction, and the power supply is a relatively straight-forward multirail linear supply, it’s far less difficult to keep going than a lot of other gear, particularly anything current that is “budget” and surface-mount tech. The M-500 series was “budget” but 1980s budget vs contemporary budget is a whole different grade of product IMO. The M-500 wasn’t built to be disposable. There are plenty of more robust and reliable designed and products, but it’s as reliable as you’d need for 1980s vintage. I wouldn’t get worried about its demise. It’ll need recapping. It’ll need other work eventually. But it’s not a bad console to own if you want something that’s likely to keep working for a long time yet, and likely be fixable when the time comes it needs some work.
R
RFR
Well-known member
True.
I think the only thing difficult to get is some of the connectors.
I think compared to some of the later Mackie mixers the 520 is a breeze to work on.
I think the only thing difficult to get is some of the connectors.
I think compared to some of the later Mackie mixers the 520 is a breeze to work on.
sweetbeats
Reel deep thoughts...
You mean, like, the power supply cable connectors? All the rest of the connectors internally are mini Molex type and readily available…standard pitch…and the power supply connectors parts are all still in good stock at Mouser. I honestly don’t think there’s anything component-wise you can’t find right now except for a lot of the pots. But that’s pretty normal…the pots in most cases have lots of life left and I think where people think the pot is worn, because of skritchies, that’s often a coupling cap issue. You can measure for DC volts between ground and the input of a pot and the DC should be 0…if there’s DC volts that will cause crackles and skritchies. The DC volts come from the offset of the opamp upstream from the pot and the coupling caps are supposed to block it, but as they age and fall out of spec they don’t do it as well.