I have a pair of GFA-565 Monobloc amps, I bought them off ebay and received them today.
The working GFA-565 had two INAPPROPRIATE 10A fuses {unknown manufacturer} for the DC rails (correct fuses should be BUSSMAN ABC-12A/250V, SOC CES6-12A/125V, or LITTELFUSE 3AG314012/250V fuses) and one INAPPROPRIATE Bussman AGC15 fuse (correct fuse should be Bussman ABC-15/250V, LITTELFUSE 3AG314015/250V, or SOC CES6-15A/125V).
NOTE: I did not know that the working unit had inappropriate fuses until after this whole experience.
I powered up and was using the working unit (with INAPPROPRIATE fuses) for an hour, experiencing the power of the massive amplifier, and it sounded great.
Then I decided to troubleshoot the other GFA-565 unit that is broken.
I took the top cover off, disconnected the fan, plugged it in, and switched it on: nothing.
After a while, I decided to take the fuses from the working unit (INAPPROPRIATE fuses) and put them into the broken unit, to see if it would work {remember at this point I did not realize that these fuses were inappropriate}).
I installed the INAPPROPRIATE fuses from the working unit into the broken one (with the power cable unplugged of course) and plugged it in.
Next I switched on the power and the power LED lights up!
BUT immediately afterwards one of the massive 100V 35,000uF ADCOM capacitors shoots off a sharp stream of smoke and the horrible smell fills the air. The instant I saw this I immediately switched off the unit and unplugged it (under 2 seconds from being switched on). Now I see the smoke and smell the crap in the air: oh no.
I took my multimeter and (making sure I probed the terminals correctly {positive to positive, etc.} I checked the status of each capacitor. One capacitor had a charge of about 67V and the other had no charge....hmmm interesting. Here is another interesting thing, the capacitors are parallel to each other. The one to the rear of the unit has the positive on the right side, and the negative lead on the left...while the capacitor to the front of the unit is rotated so that the positive lead is on the left side and the negative on the right side. The wiring is complicated so I am not sure whether that is just the way they are positioned inside the chassis or whether some unqualified technician has accidentally reversed the polarity on these caps. I do know that some work has been done on both of these amps. The previous owner (a complete idiot to be using INAPPROPRIATE fuses) had input level controls "professionally installed." God only knows what that means...and apparently, in the service manual, it says that the 25V, 220uF electrolytic capacitors on the input PCB assembly (the one everyone has problems with) have been replaced.
After about 5 minutes, the capacitor was drained and the other one was still at zero.
I removed the fuses and saw that that two rail fuses were not blown but the AC fuse was blown.
What happened here. These INAPPROPRIATE fuses worked fine on the flawless unit but when I connected them to the malfunctioning unit, it had such a violent reaction with the capacitor smoking, making hissing noises, and probably getting ready to blow up in my face.
Once again, I DID NOT CHECK THE FUSES THAT I TOOK FROM THE WORKING UNIT AND ONLY NOW DO I KNOW THAT THE PREVIOUS IDIOT OWNER HAD WRONG FUSES. But interestingly, I think that the problem was not caused by the fuses. One capacitor had charge and the other did not charge at all.
Tomorrow I want to go to Home Depot and get the appropriate fuses and then try again. But I suspect that the exact same thing will happen.
Thoughts, comments, and HELP will be much appreciated. I will attach pictures tomorrow.
The working GFA-565 had two INAPPROPRIATE 10A fuses {unknown manufacturer} for the DC rails (correct fuses should be BUSSMAN ABC-12A/250V, SOC CES6-12A/125V, or LITTELFUSE 3AG314012/250V fuses) and one INAPPROPRIATE Bussman AGC15 fuse (correct fuse should be Bussman ABC-15/250V, LITTELFUSE 3AG314015/250V, or SOC CES6-15A/125V).
NOTE: I did not know that the working unit had inappropriate fuses until after this whole experience.
I powered up and was using the working unit (with INAPPROPRIATE fuses) for an hour, experiencing the power of the massive amplifier, and it sounded great.
Then I decided to troubleshoot the other GFA-565 unit that is broken.
I took the top cover off, disconnected the fan, plugged it in, and switched it on: nothing.
After a while, I decided to take the fuses from the working unit (INAPPROPRIATE fuses) and put them into the broken unit, to see if it would work {remember at this point I did not realize that these fuses were inappropriate}).
I installed the INAPPROPRIATE fuses from the working unit into the broken one (with the power cable unplugged of course) and plugged it in.
Next I switched on the power and the power LED lights up!
BUT immediately afterwards one of the massive 100V 35,000uF ADCOM capacitors shoots off a sharp stream of smoke and the horrible smell fills the air. The instant I saw this I immediately switched off the unit and unplugged it (under 2 seconds from being switched on). Now I see the smoke and smell the crap in the air: oh no.
I took my multimeter and (making sure I probed the terminals correctly {positive to positive, etc.} I checked the status of each capacitor. One capacitor had a charge of about 67V and the other had no charge....hmmm interesting. Here is another interesting thing, the capacitors are parallel to each other. The one to the rear of the unit has the positive on the right side, and the negative lead on the left...while the capacitor to the front of the unit is rotated so that the positive lead is on the left side and the negative on the right side. The wiring is complicated so I am not sure whether that is just the way they are positioned inside the chassis or whether some unqualified technician has accidentally reversed the polarity on these caps. I do know that some work has been done on both of these amps. The previous owner (a complete idiot to be using INAPPROPRIATE fuses) had input level controls "professionally installed." God only knows what that means...and apparently, in the service manual, it says that the 25V, 220uF electrolytic capacitors on the input PCB assembly (the one everyone has problems with) have been replaced.
After about 5 minutes, the capacitor was drained and the other one was still at zero.
I removed the fuses and saw that that two rail fuses were not blown but the AC fuse was blown.
What happened here. These INAPPROPRIATE fuses worked fine on the flawless unit but when I connected them to the malfunctioning unit, it had such a violent reaction with the capacitor smoking, making hissing noises, and probably getting ready to blow up in my face.
Once again, I DID NOT CHECK THE FUSES THAT I TOOK FROM THE WORKING UNIT AND ONLY NOW DO I KNOW THAT THE PREVIOUS IDIOT OWNER HAD WRONG FUSES. But interestingly, I think that the problem was not caused by the fuses. One capacitor had charge and the other did not charge at all.
Tomorrow I want to go to Home Depot and get the appropriate fuses and then try again. But I suspect that the exact same thing will happen.
Thoughts, comments, and HELP will be much appreciated. I will attach pictures tomorrow.
The previous owner said that a repair shop told him that one of the giant capacitors and the rectifier diode in the power supply needed to be replaced. That information might help.
Here are pictures.
http://www.flickr.com/photos/49493821@N00/375230429/
http://www.flickr.com/photos/49493821@N00/375230430/
http://www.flickr.com/photos/49493821@N00/375230445/
http://www.flickr.com/photos/49493821@N00/375230449/
http://www.flickr.com/photos/49493821@N00/375230450/
Here are pictures.
http://www.flickr.com/photos/49493821@N00/375230429/
http://www.flickr.com/photos/49493821@N00/375230430/
http://www.flickr.com/photos/49493821@N00/375230445/
http://www.flickr.com/photos/49493821@N00/375230449/
http://www.flickr.com/photos/49493821@N00/375230450/
Hi again!
I do believe that the bridge rectifier (part # KBPC3504P) and that damaged capacitor both need to be replaced.
I found the exact part of the bridge rectifier and I can order it and install it.
But I have a question about replacing the capacitors. They are no longer made so I will have to use different parts.
Continuing this discussion here: http://www.diyaudio.com/forums/showthread.php?threadid=63032
Can I safely replace both of the ADCOM 100V / 35,000uF capacitors with 100V / 39,000uF capacitors???
Could a malfunctioning/broken bridge rectifier be causing AC volts to go to those caps instead of DC? Perhaps that could be causing the violent reactions. And this diagnosis would agree with the repair shop's diagnosis.
Thanks in advance...
I do believe that the bridge rectifier (part # KBPC3504P) and that damaged capacitor both need to be replaced.
I found the exact part of the bridge rectifier and I can order it and install it.
But I have a question about replacing the capacitors. They are no longer made so I will have to use different parts.
Continuing this discussion here: http://www.diyaudio.com/forums/showthread.php?threadid=63032
Can I safely replace both of the ADCOM 100V / 35,000uF capacitors with 100V / 39,000uF capacitors???
Could a malfunctioning/broken bridge rectifier be causing AC volts to go to those caps instead of DC? Perhaps that could be causing the violent reactions. And this diagnosis would agree with the repair shop's diagnosis.
Thanks in advance...
You can replace the capacitors with the 39.000µF/100V ones. Respect the polarity.
Change the bridge as well. Also here, make sure to connect it correctly. + to +, - to -, ~ to ~
The strip between both caps (Negative from first cap to positive from second cap is normal. Don't change that.
Make sure to test with a suitable fuse, preferably one with a 1/4 lower rating then what finally should be used.
Best is using a variac in combination with a 60 to 100W light bulb in series with one of the mains wires.
In any case, take care and check everything twice before applying power.
/Hugo
Change the bridge as well. Also here, make sure to connect it correctly. + to +, - to -, ~ to ~
The strip between both caps (Negative from first cap to positive from second cap is normal. Don't change that.
Make sure to test with a suitable fuse, preferably one with a 1/4 lower rating then what finally should be used.
Best is using a variac in combination with a 60 to 100W light bulb in series with one of the mains wires.
In any case, take care and check everything twice before applying power.
/Hugo
Don't use a variac or bulb without reading the service manual!!!
Can't use a variac or light bulb in series on the main with this amp unless you bypass the soft start circuit!!!!!
If you don't, you'll smoke the large ceramic wirewound that is on the soft start board.
This is noted in the service manual.
And no, the wrong fuses didn't cause the problem. Most likely, the amp had a bad cap which caused the bridge to go. Now, due to using the large fuses, you may be replacing many more parts...
I'm a bit puzzled why you powered it up when the seller told you that it needed the cap and bridge replaced.
Can't use a variac or light bulb in series on the main with this amp unless you bypass the soft start circuit!!!!!
If you don't, you'll smoke the large ceramic wirewound that is on the soft start board.
This is noted in the service manual.
And no, the wrong fuses didn't cause the problem. Most likely, the amp had a bad cap which caused the bridge to go. Now, due to using the large fuses, you may be replacing many more parts...
I'm a bit puzzled why you powered it up when the seller told you that it needed the cap and bridge replaced.
Re: Don't use a variac or bulb without reading the service manual!!!
Correct, the service manual did state that....The seller said he wasn't sure about what components were broken, just what the repair shop told him... I also did not know which capacitor was broken. I am trying to acquire either an original 100V/35,000uF Adcom capacitor (used) and a bridge rectifier and change those parts. Could anything else have been damaged in my little experiment earlier?
Also, if one capacitor is obviously broken, could the other one be damaged or does it either work or not work...? What I'm getting at is...if I find an exact replacement for the broken capacitor (from someone with another GFA-565)..is it smart to just replace the broken cap? Or should I start by replacing both caps? I am on a budget.
Also, what do you think the issue is here? Broken rectifier that damaged the capacitor? Or did the capacitor go first? What is the source of this problem.
Thanks in advance...
Apogee said:Can't use a variac or light bulb in series on the main with this amp unless you bypass the soft start circuit!!!!!
If you don't, you'll smoke the large ceramic wirewound that is on the soft start board.
This is noted in the service manual.
And no, the wrong fuses didn't cause the problem. Most likely, the amp had a bad cap which caused the bridge to go. Now, due to using the large fuses, you may be replacing many more parts...
I'm a bit puzzled why you powered it up when the seller told you that it needed the cap and bridge replaced.
Correct, the service manual did state that....The seller said he wasn't sure about what components were broken, just what the repair shop told him... I also did not know which capacitor was broken. I am trying to acquire either an original 100V/35,000uF Adcom capacitor (used) and a bridge rectifier and change those parts. Could anything else have been damaged in my little experiment earlier?
Also, if one capacitor is obviously broken, could the other one be damaged or does it either work or not work...? What I'm getting at is...if I find an exact replacement for the broken capacitor (from someone with another GFA-565)..is it smart to just replace the broken cap? Or should I start by replacing both caps? I am on a budget.
Also, what do you think the issue is here? Broken rectifier that damaged the capacitor? Or did the capacitor go first? What is the source of this problem.
Thanks in advance...
I have been disassembling the amp further...I took out the capacitors and am looking to replace both of them in addition to the bridge rectifier. Right now I pulled out the AC INPUT/BIAS TIME-DELAY PCB and am looking at it to see if there is any visible damage and there doesn't appear to be any damage at all to this component. It looks and smells fine.
How can I test this part by itself to see if it works without damaging it?
Pic is here: http://www.flickr.com/photos/49493821@N00/375850028/
ALSO: On the bottom of the amp, I found this resistor or diode sitting openly! What on earth is it doing there? I suspect that the previous owner sent the unit to a real idiot who did a bad job.
Is it a resistor? Pic is here: http://www.flickr.com/photos/49493821@N00/375850023/in/photostream/
How can I test this part by itself to see if it works without damaging it?
Pic is here: http://www.flickr.com/photos/49493821@N00/375850028/
ALSO: On the bottom of the amp, I found this resistor or diode sitting openly! What on earth is it doing there? I suspect that the previous owner sent the unit to a real idiot who did a bad job.
Is it a resistor? Pic is here: http://www.flickr.com/photos/49493821@N00/375850023/in/photostream/
Hi MJR,
Just test the large resistor at the end of the soft start board. Make sure it measures correctly and isn't open. Everything else on the board most likely is fine.
Nice diode...maybe a mouse brought it in...
In all seriousness, the boards are labeled, just make sure all of the holes are filled. If not, you've found your spot. If you have an empty spot, then check the manual to figure out what should be there...
Regarding the caps, buy new ones if you can. Don't be hung up on the 35,000 as you could go higher with no problems. Just be sure to maintain the 100v (or higher) rating. Replace the caps in both amps if you can so everything is matched.
The high the uf rating the better the bass to a point. Hence why I'd match both sides.
You can use a variac to test the amp once you replace the bad parts. You just need to jumper that big resistor at the end of the soft start board.
Good luck,
Just test the large resistor at the end of the soft start board. Make sure it measures correctly and isn't open. Everything else on the board most likely is fine.
Nice diode...maybe a mouse brought it in...
In all seriousness, the boards are labeled, just make sure all of the holes are filled. If not, you've found your spot. If you have an empty spot, then check the manual to figure out what should be there...
Regarding the caps, buy new ones if you can. Don't be hung up on the 35,000 as you could go higher with no problems. Just be sure to maintain the 100v (or higher) rating. Replace the caps in both amps if you can so everything is matched.
The high the uf rating the better the bass to a point. Hence why I'd match both sides.
You can use a variac to test the amp once you replace the bad parts. You just need to jumper that big resistor at the end of the soft start board.
Good luck,
My findings from probing the AC INPUT/BIAS TIME-DELAY ('soft start') PCB:
Resistors
The large resistor (Riken 20W/4.7ohms {part #: CR20P}) has no resistance (I think that means that it is "open"). When i put my multimeter test leads on the resistor's terminals, the analog needle jumps all the way to the right. When I test the small resistor (Riken 10W 680 ohms), it shows resistance because the needle only climbs up half way.
Diodes
I believe that both (single leaded) diodes work because the analog needle only shows resistance when the polarity is correct on the diode...showing that the diode's function of keeping electric flow one-way is working (is this good logic?) There are three 3-leaded diodes (one zener) which I did not test. Where do I put my multimeter probes to test them?
Capacitors
Regarding the capacitors, if I am going to be changing that big resistor, I think I will want to change these 20year old electrolytic capacitors as well.
Two more questions: what does the "RELAY" do? It is mounted on the soft start board and is a black box, the service manual says the spec on the relay are "125V/30A/24VDC" and the part number is 81-629-0. How can I test the relay to make sure it is not broken?
Also, I took out the bridge rectifier {the repair shop told the previous owner that this needed to be replaced} and found that the part number marked on it is KBPC3504, but the service manual says that the part number is KBPC3504P (which is produced by Won Top Electronics, here is a schematic )
Now, I have found a part called KBPC3504 (without the P) and it has the same electrical specifications and is the same construction and size as the other one...AND I can buy it for $4.70 from a US store, but it is manufactured by a completely different manufacturer. Now, the old (presumably broken) rectifier does not have the P suffix at the end of the model name on it, but the service manual has the P suffix specified in the part number.
Here is my question: can I use this one (without the P suffix) safely? Here is the link and here is the schematic.
Finally, HERE is a picture of my current (presumably broken) bridge rectifier.
Thank you guys so much for your help, Apogee especially and also Netlist for your input earlier in the thread.
Resistors
The large resistor (Riken 20W/4.7ohms {part #: CR20P}) has no resistance (I think that means that it is "open"). When i put my multimeter test leads on the resistor's terminals, the analog needle jumps all the way to the right. When I test the small resistor (Riken 10W 680 ohms), it shows resistance because the needle only climbs up half way.
Diodes
I believe that both (single leaded) diodes work because the analog needle only shows resistance when the polarity is correct on the diode...showing that the diode's function of keeping electric flow one-way is working (is this good logic?) There are three 3-leaded diodes (one zener) which I did not test. Where do I put my multimeter probes to test them?
Capacitors
Regarding the capacitors, if I am going to be changing that big resistor, I think I will want to change these 20year old electrolytic capacitors as well.
Two more questions: what does the "RELAY" do? It is mounted on the soft start board and is a black box, the service manual says the spec on the relay are "125V/30A/24VDC" and the part number is 81-629-0. How can I test the relay to make sure it is not broken?
Also, I took out the bridge rectifier {the repair shop told the previous owner that this needed to be replaced} and found that the part number marked on it is KBPC3504, but the service manual says that the part number is KBPC3504P (which is produced by Won Top Electronics, here is a schematic )
Now, I have found a part called KBPC3504 (without the P) and it has the same electrical specifications and is the same construction and size as the other one...AND I can buy it for $4.70 from a US store, but it is manufactured by a completely different manufacturer. Now, the old (presumably broken) rectifier does not have the P suffix at the end of the model name on it, but the service manual has the P suffix specified in the part number.
Here is my question: can I use this one (without the P suffix) safely? Here is the link and here is the schematic.
Finally, HERE is a picture of my current (presumably broken) bridge rectifier.
Thank you guys so much for your help, Apogee especially and also Netlist for your input earlier in the thread.
The purpose of that big resistor is to charge the caps slowly until they reach a certain ammount of voltage and then the relay close to get a direct connection . and the resistor has no more use until you turn on the amp again. Those big capacitors, when the are at zero volt are like short circuit for some milli seconds when you turn on the amp, this is why the lights dim a little bit.
the 3504 bridge can be replaced by any other 3504 bridge, regardless of manufacturer or prefixes, suffixes, etc......
the first 2 digits tell you the rated current, in this case 35A, and the second two digits tell you the voltage in hundreds, in this case 400V. so to replace this bridge you need a 35A/400V bridge. sice this one has obviously gone bad, go with a 40A rectifier if you can find one. usually the prefix is a manufacturer part prefix, and the suffix is used for things like temperature range, etc... of the part..... a similar thing is done with 1N400x diodes. they are all 1 amp diodes, but the voltage ratings of the diode are like this:
1N4001 ... 50V
1N4002 ... 100V
1N4003 ... 200V
1N4004 ... 400V
1N4005 ... 600V
1N4006 ... 800V
1N4007 ... 1000V
there are a few different 1N numbered diodes that use the same method of identifying the PRV of the diode.
the first 2 digits tell you the rated current, in this case 35A, and the second two digits tell you the voltage in hundreds, in this case 400V. so to replace this bridge you need a 35A/400V bridge. sice this one has obviously gone bad, go with a 40A rectifier if you can find one. usually the prefix is a manufacturer part prefix, and the suffix is used for things like temperature range, etc... of the part..... a similar thing is done with 1N400x diodes. they are all 1 amp diodes, but the voltage ratings of the diode are like this:
1N4001 ... 50V
1N4002 ... 100V
1N4003 ... 200V
1N4004 ... 400V
1N4005 ... 600V
1N4006 ... 800V
1N4007 ... 1000V
there are a few different 1N numbered diodes that use the same method of identifying the PRV of the diode.
Thank you ostie01 and unclejed613, I just placed a $30 order, which includes enough capacitors to replace ALL electrolytics (except the big ones) in both my 565 amplifiers (don't worry I checked and double checked each capacitor type and they all match) and two brand new 400V/35A bridge rectifiers, I'm going to replace the one in my other amp as well.
I am still uncertain whether the soft-start circuit functions or not. I will connect the new bridge rectifier and see once I get it.
I still am looking and shopping around for the filter capacitors. Because of the Class A design of this amp and the commercial power supply design, it seems to depend on a set of very large filter capacitors (wired in parallel in the bridge rectifier circuit) to filter the DC current and provide energy reserve for power demands. I do, however, insist upon a very high quality set of capacitors as they will surely have an influence on the final output of the sound.
Due to budget constraints, I would ideally like to spend no more than $50 per capacitor, but may even opt for a cheaper solution for the time being, and then upgrade to very high quality capacitors later.
I am, however, extremely glad that I underwent this process. I have learned so much and accumulated a wealth of knowledge in the past few days that I would not have acquired had I waited and bought a functioning pair of GFA-565 monoblocs later. I now have stepped beyond the looking-glass of high-end "audiophile" audio amplifiers and now am analyzing the internal circuitry and finding weak points, fixing, and modifying this amp for better sound.
Finally, I now have instant respect for all of you diy amplifier builders on this site. Kudos to everyone here and special thanks to all of you who contributed to helping me.
I will keep you updated on the type of filter capacitors that I select.
I am still uncertain whether the soft-start circuit functions or not. I will connect the new bridge rectifier and see once I get it.
I still am looking and shopping around for the filter capacitors. Because of the Class A design of this amp and the commercial power supply design, it seems to depend on a set of very large filter capacitors (wired in parallel in the bridge rectifier circuit) to filter the DC current and provide energy reserve for power demands. I do, however, insist upon a very high quality set of capacitors as they will surely have an influence on the final output of the sound.
Due to budget constraints, I would ideally like to spend no more than $50 per capacitor, but may even opt for a cheaper solution for the time being, and then upgrade to very high quality capacitors later.
I am, however, extremely glad that I underwent this process. I have learned so much and accumulated a wealth of knowledge in the past few days that I would not have acquired had I waited and bought a functioning pair of GFA-565 monoblocs later. I now have stepped beyond the looking-glass of high-end "audiophile" audio amplifiers and now am analyzing the internal circuitry and finding weak points, fixing, and modifying this amp for better sound.
Finally, I now have instant respect for all of you diy amplifier builders on this site. Kudos to everyone here and special thanks to all of you who contributed to helping me.
I will keep you updated on the type of filter capacitors that I select.
Bridge rectifier
Hi:
I would go with a 3506 rect to get the higher Peak Inverse Voltage 600V . This is another safety precaution and will in NO way affect the operation of the amp , just add some more safety.
I do not think that you need a higher current capacity but I guess that if you can find a 40 to 60 Amp 600 PIV bridge go for it !
The PIV of the diodes in a bridge rectifier have to be at least 2.828 times higher than the ENTIRE secondary winding voltage. I generally just try for 3X the sec voltage to be safe.
Hope this helps
Ed
Hi:
I would go with a 3506 rect to get the higher Peak Inverse Voltage 600V . This is another safety precaution and will in NO way affect the operation of the amp , just add some more safety.
I do not think that you need a higher current capacity but I guess that if you can find a 40 to 60 Amp 600 PIV bridge go for it !
The PIV of the diodes in a bridge rectifier have to be at least 2.828 times higher than the ENTIRE secondary winding voltage. I generally just try for 3X the sec voltage to be safe.
Hope this helps
Ed
Re: Bridge rectifier
Ed, good point...
I have already ordered the 3504, but if the amp works with what I have ordered, I will (later) upgrade the rectifier to a higher rated version, just to be safe...with more research...it's never a bad idea to go the safe route in the power supply.
Have you read THIS article? On the first page it shows the schematic for the type of commercially-produced power supply in the 565 and on the second page of that article it has a schematic for a serious power supply with dual bridge rectifiers! The little heatsink upon which the KBPC3504 rectifier rests within the GFA-565 is big enough to support another KBPC3504...I wonder if I can just wire another bridge rectifier in series?
Here is a PIC of the rectifier installed onto the heatsink inside the chassis of the 565, physically located between the AC INPUT/BIAS TIME-DELAY PCB (Soft Start circuit) and the Torroidal Transformer.
Here is a PIC of the broken KBPC3504 bridge rectifier resting atop the heatsink. My replacement KBPC3504 made by HVAC will be here sometime next week.
Ed, good point...
I have already ordered the 3504, but if the amp works with what I have ordered, I will (later) upgrade the rectifier to a higher rated version, just to be safe...with more research...it's never a bad idea to go the safe route in the power supply.
Have you read THIS article? On the first page it shows the schematic for the type of commercially-produced power supply in the 565 and on the second page of that article it has a schematic for a serious power supply with dual bridge rectifiers! The little heatsink upon which the KBPC3504 rectifier rests within the GFA-565 is big enough to support another KBPC3504...I wonder if I can just wire another bridge rectifier in series?
Here is a PIC of the rectifier installed onto the heatsink inside the chassis of the 565, physically located between the AC INPUT/BIAS TIME-DELAY PCB (Soft Start circuit) and the Torroidal Transformer.
Here is a PIC of the broken KBPC3504 bridge rectifier resting atop the heatsink. My replacement KBPC3504 made by HVAC will be here sometime next week.
Hi mjraudio,
Your bridge may have just simply failed, or failed due to the excess current draw of the cap. I normally do not see failures of the rectifier bridge even with units used by DJ's. They are fine at the original spec.
Note that your diodes within the bridge rectifier will only ever see the peak voltage across the total secondary in normal use. They may see a higher peak due to a line surge. A 400V bridge is offering a lot of headroom even on a bipolar 100V supply. Don't sweat the voltage rating.
Your amps are not class A, they are most definitely class AB. That is not a bad thing at all.
-Chris
Your bridge may have just simply failed, or failed due to the excess current draw of the cap. I normally do not see failures of the rectifier bridge even with units used by DJ's. They are fine at the original spec.
Note that your diodes within the bridge rectifier will only ever see the peak voltage across the total secondary in normal use. They may see a higher peak due to a line surge. A 400V bridge is offering a lot of headroom even on a bipolar 100V supply. Don't sweat the voltage rating.
Your amps are not class A, they are most definitely class AB. That is not a bad thing at all.
-Chris
"I am still uncertain whether the soft-start circuit functions or not. I will connect the new bridge rectifier and see once I get it."
I don't think you can test it by just hooking it up to the bridge and caps. It also has sensing circuitry that is fed from the driver board (if memory serves...)
Don't remember for sure as my amps and manual are packed right now (I just moved) but I think that's the case.
Thought I'd make this comment so you didn't think something was wrong if you hooked it up and it didn't turn on without the rest of the amp hooked up.
Others - please correct me if I'm wrong...
I don't think you can test it by just hooking it up to the bridge and caps. It also has sensing circuitry that is fed from the driver board (if memory serves...)
Don't remember for sure as my amps and manual are packed right now (I just moved) but I think that's the case.
Thought I'd make this comment so you didn't think something was wrong if you hooked it up and it didn't turn on without the rest of the amp hooked up.
Others - please correct me if I'm wrong...
anatech said:
@anatech: After seeing the component feet marks on the top cover and finding a diode sitting naked inside the unit, I don't know what to think of the previous owner(s) and what he did to this unit. Regardless, if the new parts fix the unit, I will be able to drive the amp knowing that it has a brand new rectifier and filter caps.
Also, upon reading the wikipedia article on electronic amplifiers, I now understand the difference between Class A and AB amplifiers, you are right, the GFA-565 is surely a Class AB amplifier, and very cleverly designed too in that it is pretty efficient, generating little heat.
One more thing, THIS gentleman offered some very informative advice on the GFA-565 and some issues he was having with mains voltage line surges:
@Apogee: Hmmm very useful info, thanks. I was considering hooking it up to the amp and seeing if it would work, but without the capacitors in there I would have to close the filter capacitor circuit board leads. One little error and i could damage other caps in the soft start board or possibly even the transformer and input stage. You never know. I think once I replace the rectifier, I might take the working capacitors from my other amp and install them into this broken amp and power up...Do you think that would be a bad idea?
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