I was refereed to this form from the Polk audio forum. I was having problems with my 585, noise, bias at 60mv, and running real hot at idle. I did notice the 220 caps were leaking, and nothing looked like it was on the board, so i replaced all of the lytic caps. When I powered up the amp there were a couple small explosions followed by smoke! I thought caps only blew up with an over voltage situation? voltage measured at the power suply caps is a solid 81.7. Any help would be gratefully appreciated.
Thanks Ben
Thanks Ben
O boy you mean the are sensative to polarity? Like LEDs. The long leg would be + or -
Thanks much Ben
Thanks much Ben
Yup.
The cases are usually very well marked with a stripe or similar indicating the negative pin, just hope that your PCBs are as well so you know the correct orientation.
The cases are usually very well marked with a stripe or similar indicating the negative pin, just hope that your PCBs are as well so you know the correct orientation.
OK they are polarized! The negative is the marked leg, and on the pcb there is a dot which would also signify the negative also?
Thanks much Guys, I was ready to send my amp out to a shop, and I really don't have the money to do that.
Thanks again Ben
Thanks much Guys, I was ready to send my amp out to a shop, and I really don't have the money to do that.
Thanks again Ben
Hi Ben,
Those boards need to be washed thoroughly. See other Adcom threads for details on this.
You might be further ahead to save up and send the amp into a really good shop . One that is known to be good and probably does not repair TV's and VCR's.
Once done properly, you will have a long lasting, very good amplifier.
-Chris
Those boards need to be washed thoroughly. See other Adcom threads for details on this.
You might be further ahead to save up and send the amp into a really good shop . One that is known to be good and probably does not repair TV's and VCR's.
Once done properly, you will have a long lasting, very good amplifier.
-Chris
Thanks Anatech I had recieved lots of advice about installing new caps to recitfy the original problem I had with my amp.
heres a copy of my original post at polk audio
"I have an Adcom GFA-585, and when the unit is on all by itself with no cables connected it runs pretty hot. You don't want to leave your hand on it. If you plug in the patch cables to a source it has a hum to it. I have tried multiple sources, and patch cables. Even if you don't have the preamp on, and it is still connected it still has the hum. If you play something through it the music still plays but it doesn't sound good. The bias voltage is up around 60mv. I am scared to turn it up because I don't want to blow any of my wonderful polks. "
The power suply is putting out a constant 81.7 volts.
Thanks again Ben
heres a copy of my original post at polk audio
"I have an Adcom GFA-585, and when the unit is on all by itself with no cables connected it runs pretty hot. You don't want to leave your hand on it. If you plug in the patch cables to a source it has a hum to it. I have tried multiple sources, and patch cables. Even if you don't have the preamp on, and it is still connected it still has the hum. If you play something through it the music still plays but it doesn't sound good. The bias voltage is up around 60mv. I am scared to turn it up because I don't want to blow any of my wonderful polks. "
The power suply is putting out a constant 81.7 volts.
Thanks again Ben
Hi Ben,
You need a good digital multimeter to set the bias currents. There is a procedure for this that involves dummy loads and an audio oscillator + time.
If the original caps leaked, or your new ones, the wash procedure can not be omitted. The shop must know this. An older Adcom warranty shop would be a good bet (I hope). Also, if a couple outputs blow, you need to replace the entire channel with matched sets. I don't wish to see that happen to you. Please take the safe road.
-Chris
You need a good digital multimeter to set the bias currents. There is a procedure for this that involves dummy loads and an audio oscillator + time.
If the original caps leaked, or your new ones, the wash procedure can not be omitted. The shop must know this. An older Adcom warranty shop would be a good bet (I hope). Also, if a couple outputs blow, you need to replace the entire channel with matched sets. I don't wish to see that happen to you. Please take the safe road.
-Chris
Yes I have read lots about washing the board. I do a lot of PC work, and I am good at soldering. I have 5 multi meters, and the Adcom service manual. So I don't see setting the bias as being a big deal. I really can't afford a shop to do it now, and I live in South Florida. It seems like a stupidity contest down here, and most people are tied for first place. It would cost about $100 round trip to send it somewhere I trust plus parts and labor. I can see, and appreciate your concern especially after I did something as dumb as installing some of the caps back wards. I am still kicking my self for that one.
Thanks much, I will reply with a progress report.
Ben
Thanks much, I will reply with a progress report.
Ben
Hi Ben,
That's cool. I had no idea how you were equipted and whether you had the manual or not. So you are certainly set to handle this problem.
Yeah, I have some cousins down there. I hear ya!
Just remember the board can look clean and still have residue on it. Been there, done that.
-Chris
That's cool. I had no idea how you were equipted and whether you had the manual or not. So you are certainly set to handle this problem.
LOL!
Yeah, I have some cousins down there. I hear ya!
That can, and will happen to just about everyone at some time. I've done that more than once.
Just remember the board can look clean and still have residue on it. Been there, done that.
-Chris
There are lots of Canadians down here. I am in Ft Lauderdale right next to Little Quebec (aka Hollywood). One of my best friends is from Sherbroke, and he visits a lot. Thanks again for the post.
Ben
Ben
Yes the dot should be negative.
However since most of the caps will be earthed at the negative end , you can check to see if the 'dot' end and circuit ground read near zero ohms. You can confirm the ground end from your circuit diagram.
Can you put up the circuit diagram ?
Cheers,
Ashok.
Maybe cleaning with Isopropyl alcohol after using water will help to dry up the board very fast. Should be clean Isopropyly alcohol , oterwise it will leave a residue . You can test that by applying some Iso on to a clear sheet of glass. Any residue will show up when it dries.
However since most of the caps will be earthed at the negative end , you can check to see if the 'dot' end and circuit ground read near zero ohms. You can confirm the ground end from your circuit diagram.
Can you put up the circuit diagram ?
Cheers,
Ashok.
Maybe cleaning with Isopropyl alcohol after using water will help to dry up the board very fast. Should be clean Isopropyly alcohol , oterwise it will leave a residue . You can test that by applying some Iso on to a clear sheet of glass. Any residue will show up when it dries.
Little humor at home forum
http://www.polkaudio.com/forums/showthread.php?t=46864
No smoke, playing music, still static at idle with preamp hooked up
http://www.polkaudio.com/forums/showthread.php?t=46864
No smoke, playing music, still static at idle with preamp hooked up
Yes the dot is indeed the negative side of the cap. I have it all assembled, and running, but not well. at idle with no input the cones on the speakers are extended out, and I am getting 3.6 volts on the speakers terminals on the amp.
Thanks for the post
Ben
Thanks for the post
Ben
Hi Ben,
Those guys don't know anything about amps do they? 😉
Sounds like your input grounding resistors are open. How do people do that anyway??
Measure between the RCA grounds for left and right and let me know what you get.
-Chris
Those guys don't know anything about amps do they? 😉
Sounds like your input grounding resistors are open. How do people do that anyway??
Measure between the RCA grounds for left and right and let me know what you get.
-Chris
Wide open no continuity, or Resistance at all. Measured from the outside jacket from the RCA inputs to ground.
Hi Ben,
Told ya. 😀 There are a pair of 10 ohm resistors on the input PCB's that are open.
When your preamp was connected, you got your ground through the preamp and AC ground back to the amp. That's why it was noisy and also why you had a DC offset with no inputs connected.
-Chris
Told ya. 😀 There are a pair of 10 ohm resistors on the input PCB's that are open.
When your preamp was connected, you got your ground through the preamp and AC ground back to the amp. That's why it was noisy and also why you had a DC offset with no inputs connected.
-Chris
Hi Ben,
I can't read the component designations (or the values) very well. They can be traced easily with an ohmmeter. They are in the same area as the input circuit.
Look for brown-black-black colour bands. They are probably metal film and may have more bands (aside from the tolerance band). One side will have continuity to the RCA ground. THe other will have continuity to the circuit ground (bar across the capacitors). Right now they will measure open. There are probably no burn marks, but there may be if you are lucky.
-Chris
I can't read the component designations (or the values) very well. They can be traced easily with an ohmmeter. They are in the same area as the input circuit.
Look for brown-black-black colour bands. They are probably metal film and may have more bands (aside from the tolerance band). One side will have continuity to the RCA ground. THe other will have continuity to the circuit ground (bar across the capacitors). Right now they will measure open. There are probably no burn marks, but there may be if you are lucky.
-Chris
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