Chris, you and Gregory were both right...
I got the regulator taken care of, and replaced the parts that burnt last time...but I replaced R243 with a 1K 1/2W resistor. It seems to work fine. A 10K may have even been alright, but this might affect the time it takes for the DC detection to react. Since even with a 1K resistor current is limited to managable values, I think I'll just leave it.
'Preciate the input. Thanks again.
I got the regulator taken care of, and replaced the parts that burnt last time...but I replaced R243 with a 1K 1/2W resistor. It seems to work fine. A 10K may have even been alright, but this might affect the time it takes for the DC detection to react. Since even with a 1K resistor current is limited to managable values, I think I'll just leave it.
'Preciate the input. Thanks again.
Reading this thread prompted me to open up a A502 that has been sitting in the corner of my bench for several years now. The amplifier is a royal pain in the a** to work on because the thing needs to come apart 1/2 way in order to do anything with it. Anyway it has the no latch up problem and upon inspection also had the wrong value resistor in the R243 slot. The schematic calls for a 10 ohm and this baby has a 15K in its place. I pulled the 15K and put a 10 ohm back in and promptly smoked it upon turn on. After replacing the caps in the protection circuit and a bad zenor diode I put the 15K back in and fired it back up. It didn't smoke the resistor and latched up after about a 5 second delay after turn on. I did learn that a speaker selection must be made or one will wait and noting will latch up.
Unfortunately I assembled the amplifier again without testing it and too my surprise I now have a negative waveform clip in channel B. Any ideas before I tear it back apart again? Bad connection? Bad driver transistor?
Unfortunately I assembled the amplifier again without testing it and too my surprise I now have a negative waveform clip in channel B. Any ideas before I tear it back apart again? Bad connection? Bad driver transistor?
I am the owner of this amp. Echowars did a good job on this amp! I am the original owner (purchased amp new in 1989) and this amp was never worked on before EchoWars took the task on of fixing it.
Funniest part in the saga is it has failed again. I have a buddy of mine locally working on it with me now. I am a Computer tech not a Electronics tech and he is guiding me along the way.
The problem now is that the amp works intermittently (actually one time I ran it 24x7 for 4 days before it decided to disengage the speakers) in that the protection circuit will kick in correctly (5-6 seconds) and then sometimes not at all!
My buddy found quite a few mistakes within the published schematics, we are correcting it as we go ahead with troubleshooting the "issues". Lastly, I have forwarded to him this thread and will beg him to update it with our progress.
Yank
Funniest part in the saga is it has failed again. I have a buddy of mine locally working on it with me now. I am a Computer tech not a Electronics tech and he is guiding me along the way.
The problem now is that the amp works intermittently (actually one time I ran it 24x7 for 4 days before it decided to disengage the speakers) in that the protection circuit will kick in correctly (5-6 seconds) and then sometimes not at all!
My buddy found quite a few mistakes within the published schematics, we are correcting it as we go ahead with troubleshooting the "issues". Lastly, I have forwarded to him this thread and will beg him to update it with our progress.
Yank
At the very least, this does not appear to be the same issue I addressed. I'm thinking logic issue now.bigyank said:The problem now is that the amp works intermittently (actually one time I ran it 24x7 for 4 days before it decided to disengage the speakers) in that the protection circuit will kick in correctly (5-6 seconds) and then sometimes not at all!
Indeed, I'd like to see what else he found that is incorrect in the manual.
I am gathering information to add to the thread but as a novice I do have to add someting. If my unit, which I know was never opened before EchoWars got it and the schematic both list 10 ohm resistor in the R243 slot, why would one use such a large value resistor as a replacement?
Kind of like having a 2 amp resistor go south on a piece of electronics so replace it with a 8 amp one. Just wondering how 15K came into the picture or 10K for that matter.
As for the logic circuit, the IC's were replaced with ones that EchoWars so graciously sent back to me with the amp.
Yank
Kind of like having a 2 amp resistor go south on a piece of electronics so replace it with a 8 amp one. Just wondering how 15K came into the picture or 10K for that matter.
As for the logic circuit, the IC's were replaced with ones that EchoWars so graciously sent back to me with the amp.
Yank
Hi bigyank,
As I recall, there is no way a 10R resistor could be used in that spot. It would allow much heavier currents to flow than the parts can withstand. My guess is a schematic typo (this happens more than you want to know). The original value may have been 10 K, or some other random value for all we know.
-Chris
As I recall, there is no way a 10R resistor could be used in that spot. It would allow much heavier currents to flow than the parts can withstand. My guess is a schematic typo (this happens more than you want to know). The original value may have been 10 K, or some other random value for all we know.
-Chris
Hi Echo, I recognize you from the AK board. You matched a pair of differential transistors for me awhile back (soundcraftsmen)...
Your schematic isn't showing up for me, but those SAE amplifiers (at least the ones I've worked on) have matched resistors all throught the pre, and driver circuitry. Man, there everywhere...
Best Regards, Tom
Your schematic isn't showing up for me, but those SAE amplifiers (at least the ones I've worked on) have matched resistors all throught the pre, and driver circuitry. Man, there everywhere...
Best Regards, Tom
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