Chris, good info. I'll check all those resistors today. Actually I am going to remove the output assemblies and check most everything. I really just did a visual and a simple in-board diode check on most of the transistors. So I need to do a better check on all those components.
On the good amp, on pins 3 and 4 I get 1.8vdc and -1.8vdc when it's at full power, all wires are connected, and no signal input. Seems balanced out.
gabo
On the good amp, on pins 3 and 4 I get 1.8vdc and -1.8vdc when it's at full power, all wires are connected, and no signal input. Seems balanced out.
gabo
Hi Gabo,
Have you turned the bias control right down for minimum bias current? One big clue would be to measure the voltage across each emitter resistor to see if the current is shared, or if you may have one blown output transistor.
If you have one blown output transistor, replace the set on that channel along with the driver transistors. If its just a case of excessive bias current that you can't turn down, check the resistors that go between the bases of the outputs, drivers and predriver to the output line, or to the other side directly. If one or more goes open you will not be able to turn the bias current down enough.
Good luck, Chris
Have you turned the bias control right down for minimum bias current? One big clue would be to measure the voltage across each emitter resistor to see if the current is shared, or if you may have one blown output transistor.
If you have one blown output transistor, replace the set on that channel along with the driver transistors. If its just a case of excessive bias current that you can't turn down, check the resistors that go between the bases of the outputs, drivers and predriver to the output line, or to the other side directly. If one or more goes open you will not be able to turn the bias current down enough.
Good luck, Chris
Ok, so moral of this story is... When Chris (anatech) tells you to do something, DO THAT FIRST! haha
After all the things I've read from him, I should know this by now.
So, I removed and checked resistors on the output stage boards, all good. I removed and checked several transistors, all good and decided to just do a diode test on the rest in place to see if I find anything. They all look the same.
Scratching my head, I replaced the rectifier. I ordered some that haven't come in, but it was easy to take the one out of the good unit just for a test. No luck.
Of course the last thing I did was look at the bias control R143 (and that's the first thing Anatech said to look at).. Geez it was turned all the way clockwise, full on. I hadn't even looked at it since it was a new board. But really didn't think that would cause it to go so unstable. Need to study that schematic a bit more.
But, finding nothing else, I put it back together, set R143 to the mid-point, and fired it up. Viola! no more high current draw. Tweaked the bias adjustment a bit more, but just a bit as center was almost perfect, and got a nice 24mv at the test points.
Plus/Minus 1.9vdc at pins 3, 4. 84vdc on the rails. Idle current draw from the variac at full power about 1 amp. Looking fairly good, I let it sit like that for a bit, all stable.
Powered it down and removed the jumper from the soft start board, bypassed the variac and powered it up. All stable.
Connected up a signal to the input and put my 9ohm load on the output. Checked it with the scope, all good.
There is still something not perfect about it. Running up the power, it peaks out at about 275watts before clipping. My other amp peaks at around 330watts into the same load.
I also noticed that the rail voltage sags to about 77 vdc at full power. And the caps discharge a lot faster than my other unit.
Maybe I have a bad/weak filter cap? Or maybe I have a blown/weak output transistor? Ideas and suggestions welcome?
At least I have significant progress. Thanks again to everyone here, what a great resource.
gabo
After all the things I've read from him, I should know this by now.
So, I removed and checked resistors on the output stage boards, all good. I removed and checked several transistors, all good and decided to just do a diode test on the rest in place to see if I find anything. They all look the same.
Scratching my head, I replaced the rectifier. I ordered some that haven't come in, but it was easy to take the one out of the good unit just for a test. No luck.
Of course the last thing I did was look at the bias control R143 (and that's the first thing Anatech said to look at).. Geez it was turned all the way clockwise, full on. I hadn't even looked at it since it was a new board. But really didn't think that would cause it to go so unstable. Need to study that schematic a bit more.
But, finding nothing else, I put it back together, set R143 to the mid-point, and fired it up. Viola! no more high current draw. Tweaked the bias adjustment a bit more, but just a bit as center was almost perfect, and got a nice 24mv at the test points.
Plus/Minus 1.9vdc at pins 3, 4. 84vdc on the rails. Idle current draw from the variac at full power about 1 amp. Looking fairly good, I let it sit like that for a bit, all stable.
Powered it down and removed the jumper from the soft start board, bypassed the variac and powered it up. All stable.
Connected up a signal to the input and put my 9ohm load on the output. Checked it with the scope, all good.
There is still something not perfect about it. Running up the power, it peaks out at about 275watts before clipping. My other amp peaks at around 330watts into the same load.
I also noticed that the rail voltage sags to about 77 vdc at full power. And the caps discharge a lot faster than my other unit.
Maybe I have a bad/weak filter cap? Or maybe I have a blown/weak output transistor? Ideas and suggestions welcome?
At least I have significant progress. Thanks again to everyone here, what a great resource.
gabo
Thanks Chris, that's what I suspected. Checking mouser, they are still expensive but not as expensive as they once were. Looks like an E36D, with the right case diameter, 39,000uf, 100v is now going for about $32 ea.
I should really replace all 4 as they are all the original ones from the early 90s when I purchased these new.
I'll put them in next months budget and replace those. Tomorrow I'll hook them up to some speakers and play some tunes!
gabo
I should really replace all 4 as they are all the original ones from the early 90s when I purchased these new.
I'll put them in next months budget and replace those. Tomorrow I'll hook them up to some speakers and play some tunes!
gabo
GFA-565 Replacement parts update:
I found the original JST board headers! Still manufactured and available at Digikey. Now you can keep your original wire harnesses. Apparently these connectors are popular with RC model and drone enthusiasts, for battery and servo motor connections. They are so common that the term "JST" is used to refer generically to any snap-in board header.
(SN)_sml.jpg)
Part #'s
B2B-XH-A(LF)(SN)
B3B-XH-A(LF)(SN)
From now on, these connectors will come with with my fully assembled and tested boards.
Also, I've made lots of updates to the GFA-565/585 parts list. Download here.
GFA-565 Parts List
I found the original JST board headers! Still manufactured and available at Digikey. Now you can keep your original wire harnesses. Apparently these connectors are popular with RC model and drone enthusiasts, for battery and servo motor connections. They are so common that the term "JST" is used to refer generically to any snap-in board header.
Part #'s
B2B-XH-A(LF)(SN)
B3B-XH-A(LF)(SN)
From now on, these connectors will come with with my fully assembled and tested boards.
Also, I've made lots of updates to the GFA-565/585 parts list. Download here.
GFA-565 Parts List
Yes, I had a few strange problems. Believe it or not, I actually think that I had some of the leakage from the caps on the input boards travel down the wires to the output boards and cause some problems. Especially on the side with the "brown" wire.
I just got a lot of flakey things happening, and they were intermittent.
So, I replaced the caps and also replaced all the wiring from the input boards to the output boards and things seemed to settle down.
I eventually got full expected output from both amps. They are now in my entertainment center powering my Lynnfield 500L's which are hard to power, dipping down to around 2 ohms at a couple of frequencies.
Thanks for all the help!!
gabo
I just got a lot of flakey things happening, and they were intermittent.
So, I replaced the caps and also replaced all the wiring from the input boards to the output boards and things seemed to settle down.
I eventually got full expected output from both amps. They are now in my entertainment center powering my Lynnfield 500L's which are hard to power, dipping down to around 2 ohms at a couple of frequencies.
Thanks for all the help!!
gabo
Hi gabo,
Good to hear. If your main caps were toast, that would cause your power loss. Leakage down wires into the input PCB is just too weird. I guess there is no end to really odd faults. I wouldn't have guessed at this however.
It's great your amps are doing what they were designed to do. That is the very best outcome.
-Chris
Good to hear. If your main caps were toast, that would cause your power loss. Leakage down wires into the input PCB is just too weird. I guess there is no end to really odd faults. I wouldn't have guessed at this however.
It's great your amps are doing what they were designed to do. That is the very best outcome.
-Chris
I agree Chris, the reason I suspect that though is when de-soldering the brown and blue wires on the output boards to remove the boards I smelled the tell tale "fishy" smell of the cap leakage.
I thought it was really bizarre since there is no cap on the output board in that area. The only way I can figure that could have gotten down there is by travelling down the wire from the input board.
It seemed to have been localized to the area where the brown/blue wires were connected. So cleaning up that area with QTips/alcohol and replacing the wires and the weird problems I was having went away.
The caps were weak but not totally gone, but that certainly helped as well.
Thanks to you guys for all the help.
gabo
I thought it was really bizarre since there is no cap on the output board in that area. The only way I can figure that could have gotten down there is by travelling down the wire from the input board.
It seemed to have been localized to the area where the brown/blue wires were connected. So cleaning up that area with QTips/alcohol and replacing the wires and the weird problems I was having went away.
The caps were weak but not totally gone, but that certainly helped as well.
Thanks to you guys for all the help.
gabo
Attached is a compilation of replacement parts applicable to ADCOM products. Thank you to Jim at ADCOM and Phloodpants (Chris) for your help.
Most ADCOM opamps are Linear Technology and the parts shown in parentheses are generally equivalent or better performing types.
This is also posted under 'Parts' section.
Rick
Most ADCOM opamps are Linear Technology and the parts shown in parentheses are generally equivalent or better performing types.
This is also posted under 'Parts' section.
Rick
This seems to be the most recently active 565 thread, and I thought I would share my experience with the board replacement I just finished up. I bought the already assembled and tested board, so the actual install was pretty straight forward. But during my initial power ups I was intermittently have an issue with some high current draw. After disassembling everything, checking all the fusible resistors, the output transistors (everything in this thread, thank you very much) I just couldn't find the source. I finally had the thing running at about 20v on the variac and just starting poking around, literally chopsticking (is that a word?) and found I had intermittent connections on the 3 pin connectors and moving them around would make the bias jump all over the place. Since the new board didn't require you to replace those ends I had neglected to deox them, so lesson learned but a lot of troubleshooting for a simple issue. I guess there was enough electrolytic corrosion or oxidation it was keep those from having good connections. Just thought I would share in case it would help someone out.
Thanks for all the info in the thread, very helpful!
Tim
Thanks for all the info in the thread, very helpful!
Tim
OK, I'm paranoid about this issue now! I don't want this happening to my customers. I'm going to start including new JST plugs and pins along with the GFA-565 and GFA-585 boards.
Part numbers for all three parts are...
JST Part # Digikey Description
B2B-XH-A(LF)(SN) 455-2247-ND 2-pin Board Headers
B3B-XH-A(LF)(SN) 455-2248-ND 3-pin Board Headers
XHP-2 455-2266-ND 2-pin connector housing
XHP-3 455-2219-ND 3-pin connector housing
SXH-001T-P0.6 455-1135-1-ND Connector pins
The pins are meant to be crimped by machine, but I guess they can be soldered. Anyone tried?
Part numbers for all three parts are...
JST Part # Digikey Description
B2B-XH-A(LF)(SN) 455-2247-ND 2-pin Board Headers
B3B-XH-A(LF)(SN) 455-2248-ND 3-pin Board Headers
XHP-2 455-2266-ND 2-pin connector housing
XHP-3 455-2219-ND 3-pin connector housing
SXH-001T-P0.6 455-1135-1-ND Connector pins
The pins are meant to be crimped by machine, but I guess they can be soldered. Anyone tried?