I have an old Yamaha electronic organ and it just broke. On switchone it’s okay for only about 1 second during which I can press a key and get a tone. But then a loud ‘white sound’ thing starts and continues…
I found that the main amplifier fuse 3 was burned out and it burns out again if I replace it.
So there’s too much current going though there but I can’t figure out why.
Is there anyone can help? I’ve put the circuit up on imgur:
This looks like it could be tricky. My guess would be that there is a short circuit somewhere in there. Though finding it may be difficult. I would recommend a good clean (dust can be conductive) There is also a possibility that some of the Caps have degraded and are no longer functioning properly. You may need to simulate that circuit in Something LikeLT SPICE and see if you can find it by comparing real to simulated values.
Thanks for that, Clinton. Sorry it has taken me so long to get back. I didn’t have notifications set and I got busy trying to fix the thing.
Slow laborious process because I’m not an electrician and the thing’s dangerous - live mains wiring.
anyway I fixed it but the fix didn’t last. It is broke again. I am going to start another thread about putting a new amp in there.
But this will bump this thread and, of course, I’m still interested if anyone’s got valuable info …
sorry i missed the the link to the circuit and the other pics …
if you have the know how ,replace all the small light blue electrolytic cap`s on the amp board they look somewhat tired …
there around the vertical trim pots…take note of the values that are on them…
there is a lot missing to the complete circuit…
how ever… that is the first thing i would do…
i will try find the complete circuit if i can…
EDIT: 1:
further thoughts as the complete circuit is not there i would still check the rectifier diodes D1 pair and D2 pair …since there is only one fuse on the center tap of the trans former makes it hard which side of the output circuit may be at fault if at all…given i don’t know what or if any thing else is powered by the 32 volt rails…
if you could put a cro on it that would be very handy but since you may not have one or even now how to operate one …this put`s it down to comparing voltage readings from one side to the other…with a DMM…
since you don’t have any reference check points …you may need to find a service manual for that…
i would go over the resistors checking them in circuit …with the DMM…pls note dont have the power on to do this…
i would check the low resistance resistors in the circuit first …you may find one gone very high…
EDIT:2: the 10 ohm resistor in series with the 100n cap this is the output filtering bleed off part of the circuit that connects to the zero volt rail …or the C.T rail if you will,
i bet it`s this resistor your fixing…change out the 100n for a green cap or mkt type cap…if i am correct…if your constantly replacing the 10 ohm resistor…which has no resistor number on the circuit…then try my idea below…
its more likely that the trim-pots for the bias adjustment may have become "dry" sort of like a cold solder joint for ..E.G.......these need some thin type of oil on the carbon tracks of them...and therefore after applying some oil you win need to rotate the pots around a few times… it should clear the connection to the Wiper" and carbon track of the trim pots.giving it a good connection…
…next you need to reset the bias …it is the idle voltage for the amp…
you will most likely have to have the full service manual it will most likely tell you how to set the bias correctly…
if this does not solve the problem…most likely you most likely have a bad one of the little transistors in the vas section of the amp…
EDIT :3: ok i found the manual…looked over it…seems there is no real service advice when it comes to setting the bias voltage
my advice measure the voltage across VR2…this is the bias adjustment…i am not shore what to do at present…i`ll get back to you…
Thanks for your interest and help. It’s much appreciated.
I did quite a lot of work on it - I mentioned I’d fixed it once but it came unfixed? And I was doing that with help from a forum but I can’t remember where it was or find it. I’m looking.
If I can find it again I’ll give you the link and you’ll know how much has already been done.
I had to make up a series resistance, a lamp in series in the power cord, so’s I could work on it live with some safety. But I did that and got some measurments. All this was six months ago at least, maybe a year.
And I had it out and unsoldered the power transistors and did other things.
Last thing was a suggestion I get an ESR and test some caps and I got a cheap ESR from ebay but never got to use it - had big changes at home and everything came to a stop, just looking at getting back to it now.
There’s not enough of the circuit there? The whole manual is on my site at abrogard dot com if that helps at all.
You know I’m thinking it might be safest, easiest, best to just put a new amp in there if I can find out what kind of amp I need. Could you figure that out? I’d just have to take the connecting plug off the old amp and wire in the new amp (according to instructions from such as yourself) and then plug in. Voila !
pls disregard edit 2 where the yellow marking is all that …dont touch/move VR-2…pls.
pls measure the resistance across it no power applied …
and if you can also measure it`s voltage with the power on…if at all pls…
take notes of these measurements and post them…pls
Across VR2? which way ‘across’ ? It has three legs of course…
And I can measure while it is on the board?
I don’t have time right now. I haven’t forgot. I’ll get onto it just as soon as I can… I’ll get back to you… thanks for your interest…
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