Have you measured the DC supply voltages yet (at the fuses) to check something isn't strange there? BTW, general replacement of electrolytic caps is still good practice but it's quite surprising to hear of so many of a quality brand failing before 20 years. As there are 6 of those 47uF parts, I'd just replace them all with decent quality like Panasonic FC or your favorite cool sounding brandname equivalents, maybe as you plan to. They can be tested with an ESR meter, designed specifically for checking cap performance, but that will cost as much as all the caps.
I've ordered the parts for a full recap on all boards. With such a limited part count, it didn't hurt too bad at all. Glad I chose Adcom to get my feet wet with this sort of thing, the layouts have not been overwhelming.
I do plan on testing like you suggested before outright replacing the caps. I'm a bit more tactile/visual, so I've been looking on youtube for examples of bulb limiters. This fella is testing an old guitar amp, but I assume it would work the same way for my power amp, just with a smaller wattage bulb. Is that correct?
Here's the video: https://www.youtube.com/watch?v=wRFRwOnLsZI
I do plan on testing like you suggested before outright replacing the caps. I'm a bit more tactile/visual, so I've been looking on youtube for examples of bulb limiters. This fella is testing an old guitar amp, but I assume it would work the same way for my power amp, just with a smaller wattage bulb. Is that correct?
Here's the video: https://www.youtube.com/watch?v=wRFRwOnLsZI
Hi. That video is also fine but being for tube guitar amps where the idle currents could be much higher than solid state, the bulb rating should be lower if you expect any useful level of protection and indication. Modern incandescent bulbs are likely lower rated halogen types in any case. Start at 60W or maybe a little higher according to the actual ratings available.
The focus so far has been on caps but assuming the replacement caps are all installed with correct polarity, the worst scenario should be that it is no better than when you first opened it up. But now it blows fuses. The knee-jerk reaction is that you have made an error fitting the caps there - easy to do. If you haven't and maybe you have a DMM now, would you check the rail voltages on the supply side of the empty fuse holders as asked? Your experience so far, should tell you that the measurement of each + or - supply rail voltage is with respect to ground. Post result.
Before starting, remove any external connections like speakers and input leads. Power up with replacement fuses fitted and only when the bulb limiter is in place. The bulb will flash then glow brightly as long as there's a real problem but settling to a glimmer would be normal. Confirm a short with the bulb tester and measure the voltages at the fuse holder when this is occurring.
Assuming the fault remains, remove the fuses in the bad channel again and we can look at how the other channel is faring. The bulb should only be glimmering now so measure the voltages at the fuse holders for this channel which should read much higher (in the order of +/- 50V). Now measure the voltage between the output terminals of the good channel. Anything more than 100mV DC there, either polarity, is still a problem.
The focus so far has been on caps but assuming the replacement caps are all installed with correct polarity, the worst scenario should be that it is no better than when you first opened it up. But now it blows fuses. The knee-jerk reaction is that you have made an error fitting the caps there - easy to do. If you haven't and maybe you have a DMM now, would you check the rail voltages on the supply side of the empty fuse holders as asked? Your experience so far, should tell you that the measurement of each + or - supply rail voltage is with respect to ground. Post result.
Before starting, remove any external connections like speakers and input leads. Power up with replacement fuses fitted and only when the bulb limiter is in place. The bulb will flash then glow brightly as long as there's a real problem but settling to a glimmer would be normal. Confirm a short with the bulb tester and measure the voltages at the fuse holder when this is occurring.
Assuming the fault remains, remove the fuses in the bad channel again and we can look at how the other channel is faring. The bulb should only be glimmering now so measure the voltages at the fuse holders for this channel which should read much higher (in the order of +/- 50V). Now measure the voltage between the output terminals of the good channel. Anything more than 100mV DC there, either polarity, is still a problem.
Ok, so tonight with te coaching of an electronics friend, I confirmed that my rectifiers are good.
I also tested the DC supply by putting one probe on m x01 and the other on m x02. On both channels, I'm getting around 110v.
That is higher than 50v mentioned. Does that suggest a problem with my power supply?
I also tested the DC supply by putting one probe on m x01 and the other on m x02. On both channels, I'm getting around 110v.
That is higher than 50v mentioned. Does that suggest a problem with my power supply?
There's a lot missing in your reply here, like whether you fitted a bulb limiter as discussed. Then there's whether you doubled-checked that there's no polarity error with fitting the replacement caps.
I realize from your interpretation, that I should have specified that the black probe be grounded for voltage measurements. As you measured from one fuse holder to the other, you measured across both + and - supply rails which means double each rail voltage. So, 110/2 = 55V is not too far from my rough guess of 50V. Check again that the voltages are close to equal by measuring from each fuse holder in turn to the power supply ground. Of course, they will be opposite polarity WRT ground.
Assuming the fuses were not fitted, you were simply checking the supply out but when you fit the fuses again, what did the bulb do? Read #24 again.
I realize from your interpretation, that I should have specified that the black probe be grounded for voltage measurements. As you measured from one fuse holder to the other, you measured across both + and - supply rails which means double each rail voltage. So, 110/2 = 55V is not too far from my rough guess of 50V. Check again that the voltages are close to equal by measuring from each fuse holder in turn to the power supply ground. Of course, they will be opposite polarity WRT ground.
Assuming the fuses were not fitted, you were simply checking the supply out but when you fit the fuses again, what did the bulb do? Read #24 again.
Hi,
Please, stop what you are doing and take a breath. You started with a working amplifier and managed to break it. I can't imagine why you adjusted the bias controls and whose advice you are taking in addition to the help you have been receiving here, but you have strayed a long way from a sensible course of action. I need to have you think about what you have done so far. Most importantly ... STOP!
Time to assess what you have for equipment and experience. What meter did you buy for starters? They are not all created equal, not even close. The less experience you have, the more an expensive meter you ought to buy. It takes an engineer to use a cheap meter effectively, and they wouldn't waste their time doing it.
Okay, you have done things in addition to what has been recommended by Ian. You haven't mentioned those steps, but simply proceeded to execute them (an apt term). From now on, listen to one source of information only and communicate with that source effectively. I'll admit to being a bit annoyed with what you've done, and I am a seasoned audio technician. You need some tough love for your own good here.
1. Disconnect the power lead completely - you are not going to use it for a while.
2. Discharge the power supplies with a load resistor. 10R at 25 watt is a good choice.
3. Visually examine the amplifier and write down only the defects you see.
Stop! Report these observations please. Do not talk to any other source of assistance, you don't need to be creative or confused.
If you aren't going to follow these suggestions, you are further ahead to pour gas on it, light it and walk away. Sorry, but that's the truth.
-Chris
Please, stop what you are doing and take a breath. You started with a working amplifier and managed to break it. I can't imagine why you adjusted the bias controls and whose advice you are taking in addition to the help you have been receiving here, but you have strayed a long way from a sensible course of action. I need to have you think about what you have done so far. Most importantly ... STOP!
Time to assess what you have for equipment and experience. What meter did you buy for starters? They are not all created equal, not even close. The less experience you have, the more an expensive meter you ought to buy. It takes an engineer to use a cheap meter effectively, and they wouldn't waste their time doing it.
Okay, you have done things in addition to what has been recommended by Ian. You haven't mentioned those steps, but simply proceeded to execute them (an apt term). From now on, listen to one source of information only and communicate with that source effectively. I'll admit to being a bit annoyed with what you've done, and I am a seasoned audio technician. You need some tough love for your own good here.
1. Disconnect the power lead completely - you are not going to use it for a while.
2. Discharge the power supplies with a load resistor. 10R at 25 watt is a good choice.
3. Visually examine the amplifier and write down only the defects you see.
Stop! Report these observations please. Do not talk to any other source of assistance, you don't need to be creative or confused.
If you aren't going to follow these suggestions, you are further ahead to pour gas on it, light it and walk away. Sorry, but that's the truth.
-Chris
Hi Chris, thanks for your reply. My incomplete responses and perhaps unreasonable actions are only a result of inexperience, not pride. Thanks for your patience.
I would be happy to take a visual assessment of the amp. Thus far, the only things I have done outside of Ian's advice have been testing the bridge rec's. I've purchased the parts for a bulb limiter as Ian suggested, just haven't had the time to put it into use.
My meter is an Innova 3220 auto-ranging. And I biased the amp because after the first recap, I tested the bias and both sides were running a bit hot in reference to the service manual.
I would be happy to take a visual assessment of the amp. Thus far, the only things I have done outside of Ian's advice have been testing the bridge rec's. I've purchased the parts for a bulb limiter as Ian suggested, just haven't had the time to put it into use.
My meter is an Innova 3220 auto-ranging. And I biased the amp because after the first recap, I tested the bias and both sides were running a bit hot in reference to the service manual.
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Hi asilker,
Much like the profession you are in, I become frustrated when people seem to be determined to cause themselves damage or exercise poor judgement. With your background, I was surprised that you attempted to follow the advice of non-professionals. This endeavor requires a lot of background knowledge and understanding of how these parts work.
Your adjustment of the circuit bias for example. Logic tells you that the amplifier has been running for a very long time the way it was adjusted. Therefore, alignment for bias current should be almost the last step you take.
Rule #1 - Work in a clean, clear area. Make certain the floor is clean and clear as well.
Rule #2 - Never adjust controls in a working piece of equipment that appears to be running within a normal range of acceptable performance.
Rule #3 - Make a visual inspection of the equipment noting any abnormal signs of damage or previous work. Take digital pictures at this stage, noting especially the orientation of any components you might be working with. You can't have too many high resolution pictures. Note missing or stripped screws as well. Write down your observations (only, never conclusions).
Rule #4 - Plug the equipment in if it is safe to do so. Write down any further observations at this point. Allow time for the equipment to stabilize keeping an eye out for any clues the entire time. This includes any sounds you might hear. Take key voltage readings if this will be necessary. It almost always is.
Rule $5 - Turn the equipment off. Discharge the supply capacitors using a 10 ohm, 25 watt power resistor on alligator jumper wires. Once this is done, take voltage measurements to ensure the equipment has been rendered safe to work on.
Once you have followed these steps, you can begin to inspect the equipment more closely. Take notes and only record observations. If you want, you can record conclusions, but on a separate list.
Before doing anything, you will need the following:
*Good soldering station with controlled temperature. These cost about $100 CDN and you will use it throughout the life of your hobby. This piece of equipment will directly determine the success of your endeavors.
*Half decent tools. Low quality tools will cause stripped screws and rounded nuts. Not worth the cheap stuff since good quality tools that really fit are not that expensive.
*Solder sucker (the big ones with recoil) and desoldering braid.
*A good multimeter. Plan on spending a bit over $200 for your first meter. Buy either a Fluke, Keysight Technologies (Agilent - HP), Kiethley or a good known brand. A bottom of the line Keysight will dust most other meters without too much trouble.
*An oscilloscope - you're going to need one, sorry. At least a 20 MHz, dual trace older model. The USB scopes are too easy to blow up, and so are the entry level digital oscilloscopes.
*An audio generator or function generator. Even a wien bridge oscillator will do, but it needs a level control (linear type).
*At some point you will need a distortion analyzer. Old HP 331A through 334A are excellent and not too much money.
There are cheaper bits of test equipment around, but you'll end up fighting them all the time, and the readings you get may be completely incorrect.
You are working on a good amplifier, so you really should have this stuff now. If you can get access to the equipment I listed, that's fine. But don't work without it.
Light bulb current limiter. Okay, but what you really need is a variable AC transformer. You can find them anywhere from $10 used to a very hundred for new in a box with meters and switches. The problem with the light bulb is that you can't really control the current finely. With a variac, you can increase the line voltage slowly and monitor the current (with an ammeter built in) and some point in the equipment where you are looking at a fault. So if you see a variable transformer setup, buy it. I got an nice one on Ebay, made by B&K for less than $100. It has a 5 ampere rating, meters and a leakage tester built in. Of course it is built in a nice box and has switches for changing the function of the meter. Keep your eyes open. Once you use one, you will understand why the light bulb thing really doesn't cut it.
-Chris
Much like the profession you are in, I become frustrated when people seem to be determined to cause themselves damage or exercise poor judgement. With your background, I was surprised that you attempted to follow the advice of non-professionals. This endeavor requires a lot of background knowledge and understanding of how these parts work.
Your adjustment of the circuit bias for example. Logic tells you that the amplifier has been running for a very long time the way it was adjusted. Therefore, alignment for bias current should be almost the last step you take.
Rule #1 - Work in a clean, clear area. Make certain the floor is clean and clear as well.
Rule #2 - Never adjust controls in a working piece of equipment that appears to be running within a normal range of acceptable performance.
Rule #3 - Make a visual inspection of the equipment noting any abnormal signs of damage or previous work. Take digital pictures at this stage, noting especially the orientation of any components you might be working with. You can't have too many high resolution pictures. Note missing or stripped screws as well. Write down your observations (only, never conclusions).
Rule #4 - Plug the equipment in if it is safe to do so. Write down any further observations at this point. Allow time for the equipment to stabilize keeping an eye out for any clues the entire time. This includes any sounds you might hear. Take key voltage readings if this will be necessary. It almost always is.
Rule $5 - Turn the equipment off. Discharge the supply capacitors using a 10 ohm, 25 watt power resistor on alligator jumper wires. Once this is done, take voltage measurements to ensure the equipment has been rendered safe to work on.
Once you have followed these steps, you can begin to inspect the equipment more closely. Take notes and only record observations. If you want, you can record conclusions, but on a separate list.
Before doing anything, you will need the following:
*Good soldering station with controlled temperature. These cost about $100 CDN and you will use it throughout the life of your hobby. This piece of equipment will directly determine the success of your endeavors.
*Half decent tools. Low quality tools will cause stripped screws and rounded nuts. Not worth the cheap stuff since good quality tools that really fit are not that expensive.
*Solder sucker (the big ones with recoil) and desoldering braid.
*A good multimeter. Plan on spending a bit over $200 for your first meter. Buy either a Fluke, Keysight Technologies (Agilent - HP), Kiethley or a good known brand. A bottom of the line Keysight will dust most other meters without too much trouble.
*An oscilloscope - you're going to need one, sorry. At least a 20 MHz, dual trace older model. The USB scopes are too easy to blow up, and so are the entry level digital oscilloscopes.
*An audio generator or function generator. Even a wien bridge oscillator will do, but it needs a level control (linear type).
*At some point you will need a distortion analyzer. Old HP 331A through 334A are excellent and not too much money.
There are cheaper bits of test equipment around, but you'll end up fighting them all the time, and the readings you get may be completely incorrect.
You are working on a good amplifier, so you really should have this stuff now. If you can get access to the equipment I listed, that's fine. But don't work without it.
Light bulb current limiter. Okay, but what you really need is a variable AC transformer. You can find them anywhere from $10 used to a very hundred for new in a box with meters and switches. The problem with the light bulb is that you can't really control the current finely. With a variac, you can increase the line voltage slowly and monitor the current (with an ammeter built in) and some point in the equipment where you are looking at a fault. So if you see a variable transformer setup, buy it. I got an nice one on Ebay, made by B&K for less than $100. It has a 5 ampere rating, meters and a leakage tester built in. Of course it is built in a nice box and has switches for changing the function of the meter. Keep your eyes open. Once you use one, you will understand why the light bulb thing really doesn't cut it.
-Chris
You don't need all of that to replace a few caps. OP made a mistake somewhere and now will pay for it unfortunately.
Hi ridikas,
If you ruin your own PCB, I don't really care. Good on ya! But to work on the PCB, you need the tools I listed. Period, end of story. You also need to confirm your work is done properly, and a basic test is waveform appearance and THD (should be lower after you do your thing). If you sell your wrecked amplifier - I care.
What you don't see is the 30+ years I have had to clean up after poor work. Or the times I have had to write-off equipment because some idiot decided he/she was a technician and wen to work without the skills. To someone untrained, everything looks easy. To someone who is trained and has experience, you know all the things to watch for.
When I replace capacitors for someone, I test the new ones first, then after the installation, I clean up my work and measure the performance for the equipment. However, just changing capacitors is not going to improve performance unless you install the correct type, not always what is popular on the internet.
No one else should ever be affected by someone's poor workmanship except the poor quality workman. So if you hack your own stuff, do not sell it down the road unless you disclose fully what you did and show the work. If it will not be reliable, you have no right to sell someone else the problems you created.
Now, the mistake the OP made was a tool / equipment issue - exactly what I commented on.
-Chris
Yes ... you do. Especially if you charge for the work.
If you ruin your own PCB, I don't really care. Good on ya! But to work on the PCB, you need the tools I listed. Period, end of story. You also need to confirm your work is done properly, and a basic test is waveform appearance and THD (should be lower after you do your thing). If you sell your wrecked amplifier - I care.
What you don't see is the 30+ years I have had to clean up after poor work. Or the times I have had to write-off equipment because some idiot decided he/she was a technician and wen to work without the skills. To someone untrained, everything looks easy. To someone who is trained and has experience, you know all the things to watch for.
When I replace capacitors for someone, I test the new ones first, then after the installation, I clean up my work and measure the performance for the equipment. However, just changing capacitors is not going to improve performance unless you install the correct type, not always what is popular on the internet.
No one else should ever be affected by someone's poor workmanship except the poor quality workman. So if you hack your own stuff, do not sell it down the road unless you disclose fully what you did and show the work. If it will not be reliable, you have no right to sell someone else the problems you created.
Now, the mistake the OP made was a tool / equipment issue - exactly what I commented on.
-Chris
Hi guys! Just for the record, I did start work on an amp that was NOT functioning properly. The 5300 was buzzing so loudly that more dynamic passages lacked any kind of negative space. Just idling the amp, the buzz drove me nuts.
Also unfortunately while I would love to have a workshop set up, I'm undertaking diagnostics myself in order to save money
as a grad student, my hope is to develop enough skill just to maintain my own gear, not make money commercially
Also unfortunately while I would love to have a workshop set up, I'm undertaking diagnostics myself in order to save money
as a grad student, my hope is to develop enough skill just to maintain my own gear, not make money commercially
Hi asilker,
But it was working.
To be honest with you, the job not only requires this equipment, but also some skill. We can help with the skill, but at the end of the day, you're the one doing the work. But if you don't have the equipment, or cannot get access to it, you simply cannot do the work. You have to accept that there are times that doing what you are trying to do will work out to be the most expensive option. So whether you want to be a technician or not, you still need basic skill and equipment. You are attempting to do work that Adcom only allows experienced (and good) technicians to perform. I was authorized warranty for Adcom and did work on that model. I owned the shop and did hiring and firing. New technicians didn't go anywhere near Adcom amplifiers for one.
So, I'm trying to help, but we need something to work with.
Okay, remove the fuses on the PCB, then take your new meter and check the output transistors. Are they shorted? Even one shorted means you need all of them for that channel. Check the drivers and all the way back until you start finding good ones.
Normal service for Adcom. You need to match the outputs and some other transistors. That is a normal requirement. See Nelson Pass' forum and search how to match power mosfets. You will need a power supply for that.
-Chris
But it was working.
To be honest with you, the job not only requires this equipment, but also some skill. We can help with the skill, but at the end of the day, you're the one doing the work. But if you don't have the equipment, or cannot get access to it, you simply cannot do the work. You have to accept that there are times that doing what you are trying to do will work out to be the most expensive option. So whether you want to be a technician or not, you still need basic skill and equipment. You are attempting to do work that Adcom only allows experienced (and good) technicians to perform. I was authorized warranty for Adcom and did work on that model. I owned the shop and did hiring and firing. New technicians didn't go anywhere near Adcom amplifiers for one.
So, I'm trying to help, but we need something to work with.
Okay, remove the fuses on the PCB, then take your new meter and check the output transistors. Are they shorted? Even one shorted means you need all of them for that channel. Check the drivers and all the way back until you start finding good ones.
Normal service for Adcom. You need to match the outputs and some other transistors. That is a normal requirement. See Nelson Pass' forum and search how to match power mosfets. You will need a power supply for that.
-Chris
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