HI Thanks! At the end of the day, the main fix was replacing old electrolytics - everything else I did wasn't effective. The question is: which electrolytics? Best I can say not having a schematic is that if you look at the board and the screwdriver at 21:54 you can see 2 electrolytics (one is gold - C12 and C11) immediately to the left of the screwdriver shaft. I *think* those have something to do with modifying/creating/stabilizing the reference voltage provided by the Maxim chip. But if I was starting from scratch I would replace all the electrolytics first and ignore everything else.

+Professional Repairs That's very interesting. What I imagine they might use a shift register for is to take progressive samples of the incoming voltage error. Maybe they look for a long term accumulation of error before they switch taps on the transformer. This could act as a delay mechanism in the feedback loop to prevent hunting, which was exactly the problem I was trying to solve. So it could be that my eventual solution both helped the precision of the error signals, but also, seeing as how I also had to replace some old electrolytics, that one of them was in the circuit providing a clock to the shift register, or maybe even just smoothing the error signal... very interesting.

I am having the same problem, which electrolytic you had to replace?

Well, the buzzing could be any number of things, including just that it became loose somehow and you have to tighten the bolt holding it to the chassis. Big power transformers hum, and not much to be done about that. When they start buzzing it's frequently because the hum vibration has caused a wire to become loose somewhere in the windings and now instead of just humming the wire is vibrating and hitting its neighbors and it makes a tapping sound which becomes a buzz at 60hz (in US) 50hz (UK). OR, it could be that there's literally something else loose inside the chassis, and the humming transformer is vibrating that thing, and you can just tighten it down. So, it's probably worth it to open it up and see what's what. If its the transformer itself - needs to be replaced. If its something else loose, might be a simple fix. Sorry for the long answer but there's really no way to know until you check.

You can actually get the schematic for that model now. But still, no clue how the microcontroller is programmed.

@@musicmakelightning Don't recall the E-Prom ever being a problem. And if you come across a AR-1215 that does, I'm afraid it's ready for the scrap yard. I would imagine this E-Prom programed is impossible to source. The bean counters would of surplussed that part out when the buy out happened and this model discontinued.

@@musicmakelightning This regulator was marketed to people that played guitar and bass through tube amplifiers in clubs when voltage could be unstable. Worked well for that application.

@@allenscott8225 Mine generally worked OK after this fix, but some years later exhibited the same "hunting" issue. I retired it for a new model. Yeah, maybe I just gave up. I still have it in the garage. I figured I'd use it for parts at some point.

@@musicmakelightning In all honesty if your a keyboard player primarily working from home with a steady voltage source you really don't need it. Fluctuating voltage for a guitar player using a tube amp at a show is every bit as bad as micro-phonic pre amp tubes. It will effect your amp tone to a point that it's noticeable. The big deal with these was you could use them in a recording environment without introducing any noise on too your recording. At the time there was nothing else like it on the market. It's typically a band aid for a bigger problem with power, if your in someone else's house you can't force them to fix it. These have been discontinued for a long time now. A big part of that has to do with huge technology changes in power supply technology. And auto sensing power supply's in many cases. I believe tube amps used in backline can still benefit from steady voltage.

HI Andras. I wish I could help, but unfortunately I don't really know anything about the PS-PRO models. I do have a couple M-8x AR models, and they have a function which doesn't power the outputs until after a stabilization delay of about 30 seconds. I could imagine that the delay is activated through some relays, and if your PS-PRO has the same sort of function, it could be possible that there's a capacitor somewhere that is discharging and briefly activating the output. But really, I have never used a PS-PRO and I don't have a schematic for it or I'd have a better idea. Thanks for asking, though. I appreciate your comment and hope you can get that fixed .

@@musicmakelightning No problem, thanks so much for getting back :) tried to contact furman support but no response yet

HI there. Well, buzzing on audio power supplies can be any number of things, but the obvious is the main power transformer. Power transformer buzzing in non-toroidal transformers can be caused by the core laminations coming unglued. But in the Furman there's a big toroid. I have never personally taken one of these apart so I don't know if the core contains a bunch of C shaped laminations or if it's solid ferrite of some kind. If it's ferrite, it's unlikely to be the issue as the ferrite is probably one single doughnut of solid material. There is really no cure that I know of for a transformer that has loose laminations in the core. They have to be replaced. But again, it's not entirely likely that's the case. The other, more simple possibility is that there is something loose inside that's buzzing. Could be a loose screw or even a wire that's leaning against something that's vibrating. That would be a simple matter of tightening everything down. The other thing to keep in mind is that the buzzing in power transformers increases with load. So if you have a whole lot of things drawing current, you're going to get a lot more vibration. Anyway, my bet would be that something is loose. If it turned out the transformer was hosed, well, I don't think there's a possibility to replace that. Hopefully that was useful info. Cheers.

@@musicmakelightning Thank you SO much for the thoughtful, detailed reply. I'll unscrew and take a look inside. I have a studio full of other Furman's large and small and they don't make a peep, and this buzz isn't overly offensive....if it was powering say, servers etc, but for music - not so much. It's just been such a workhorse for me, I hate to punt on it.

@@silversulu I feel the same way. I've had mine for nearly 20 years and it still works great.

I got mine from Mouser.

I really can't say from a distance like this. There are no schematics for this thing available. That was my problem. I think the easiest thing to do is to replace all the electrolytics if the unit is old. In my case, that's what it was. A bad cap. But really, there are so many sensitive parts, it's hard to suggest even where else to start. Sorry I can't be more help.

First thing to do is replace all the electrolytics. Those things are pretty old and the caps have got to be dried out by now. That's the main issue with them, far as I can see...

I just checked on mine - and R15 is a 10k resistor. However, if that guy is blown, it suggests something more sinister is going on. I would suspect one of the ICs or discrete transistors has gone on you. The good news is that those parts are generic (not like the PLA in there which needs programming) The unit I fixed in this video actually started "hunting" again after these years. I suspect it's C19 - which in my unit is a reasonably high precision (5%) capacitor which must be used in the generation of a "comparison" voltage it uses with the voltage reference. I replaced C19 and it stopped hunting for the moment). Where did you find the schematic for the AR1215j? My unit is indeed a 1215J so I would really appreciate a pointer to the schematic.

@@musicmakelightning vdocuments.mx/furman-ar1215-power-conditioning-120vac.html was where I located the schematic. R51, not R15 was the resistor blown. Does the rest of the information still appl

Ok I just found the schematic! I'm now 1000x more knowledgable than when I did that video. If your R15 blew - then you have an overcurrent situation, and I would suspect that you'll find that either U12, or U11 - or both, are toast - or c4 has failed in a short circuit. As I remember there were tantalum caps in there originally (i removed them in mine is they were there) and that could cause that issue.. Those resistors generally don't just detonate without something else going south. Of course anything is possible, but a burned R15 suggests an overcurrent (it's only a 1/4W resistor - so 5ma is going to be its max) and the only way for that to happen is for the TLO74 to be supplying too much current or the cap is shorted . So make sure you look at those when you replace R15. Also - the precision cap I'm talking about is C9 (not C19) as I mentioned before.

@@MrYoopercharged R51 is a 56 ohm 1/2 watt resistor that is on the input of Triac Q13. If that guy is blown, the Triac isn't going to work at all - and that Triac supplies the main power to the big toroid that drives the whole output. Again , that resistor isn't going to smoke unless there's an overcurrent - and in this case it only has to be sqrt(0.5/56) Amps. U15 could also be bad. That's an optoisolator, though, which is controlled by the circuitry detecting hi/lo voltage input. It could have gone to a dead short on the output...worth checking. The Q13 circuit is acting as a solid-state-relay. Normally, it will pass the input AC voltage. It gets triggered if there's an over or under voltage - and then it cuts off. The effect you are seeing - that you have absolutely no output and some/one LED lit could definitely be caused by that Triac going bad. Check Q13, U15, C29, C28 for faults when you replace R15. Oh - and C9 - what I think is bad on mine, is in a zero crossing detection circuit which is used to make sure the voltage output is only switched during periods of minimum current supply to the load. Otherwise, if its switches at peak AC current, things will generally not be happy.

@@musicmakelightning It works great now. I replaced all the components in question. C28 and C29 tested bad. I replaced everything except those two and it wouldn't function. Safety caps. I ordered the wrong ones initially and had to wait a bit. Thanks much for your help.

Hi there. Thanks for the question but actually I have never fixed that condition. I'm presuming you have what you know to be a good power source and for some reason you're getting this error with the Furman. My problem is I don't know the functioning of the microcontroller inside the Furman, and your problem could either be with that controller or with the outlying circuitry, and there's really no way to find out without getting details from the manufacturer, which are unavailable to all of us. I wish this unit were more user servicable. Maybe the newer ones are.

Sorry. Don't have it. I just found the AR1215 on line the other day. Wish I had it when I made this video.

I didn't go back to look at it again once it was working :) But I do believe those caps were bad. The unit was pretty old - and as I remember and I didn't have any sort of schematic you could kind of figure out the circuit just by looking at where things were placed. Generally - swapping the electrolytics with new ones couldn't hurt. Wish I had more evidence.

@@musicmakelightning would you be willing to look at a schematic for ours and make some educated guesses? I also have an AR-Pro doing the same thing, and absolutely do Not trust my local power with nice equipment unregulated.

@@babapambazuka2845 Hi there. Thanks for the note. I am not sure I can be of any help. There is a microprocessor in the overall mix that is programmed in some un-specified way which does play a big part. I literally just started replacing parts until it started working (thank heavens it wasn't the uP or I would have never found it). The somewhat obvious thing to do, if your unit is old, is to replace all the electrolytics, but that may not be it, either. Without some kind of service manual, it's all guesswork.