I'm trying to fix a Krell KSA-300S amp. I hope I don't have to ship it back to the manufacturer because it's so heavy. Hopefully some members here can help me troubleshoot it. I do know how to solder.
Sequence of events leading to the current problem:
1) when powering up, it has about 1 minutes of delay before the output relays clicks on.
2) recently, I can hear a "sizzle" sound (like doing B-B-Q, frying beef) when I turn on the power switch. After 1 minute, the relay clicks on and the amp is fully operational.
3) more recently, I hear louder "sizzle" sound when powering up but the amp is still fully operational.
4) most recently, after the above events, the amp will shut down. I'm assuming the protection circuits kicks in to shut down the amp. No speaker damage. This happen one time after the amp has been on for 1/2 hour. The other time, amp shut down after 2 hours. For both times, after waiting for 5 minutes, I was able to turn on the amp again. The weather here is about 90 degrees lately and I listen at regular volume level. The hot weather probably has nothing to do with this but I thought I mention it.
5) last week, when powering up, I think I hear a "crackle" sound in addition to the "sizzle" sound. Amp did power up as usual but after about 1 hour, the amp shut down. After waiting for 5 minutes, this time the amp will NOT turn on anymore.
Questions:
- I understand that capacitors went out very often and I suspect that it's the same situation here. Anybody knows which one(s)? I have not been able to find a schematics on this forum or at the Krell web site. I also suspect that the problem is on the "start up" board and I suspect (& hope) that the amp section are fine. I have done a internal visual inspection. Nothing looks burnt or leaking.
- I have done a search on this forum but I did not find anything related to KSA-300S. Lots of info on KSA-100S though but the problems are unrelated.
Any suggestions? I plan to "dive" in and do some troubleshooting soon.
Sequence of events leading to the current problem:
1) when powering up, it has about 1 minutes of delay before the output relays clicks on.
2) recently, I can hear a "sizzle" sound (like doing B-B-Q, frying beef) when I turn on the power switch. After 1 minute, the relay clicks on and the amp is fully operational.
3) more recently, I hear louder "sizzle" sound when powering up but the amp is still fully operational.
4) most recently, after the above events, the amp will shut down. I'm assuming the protection circuits kicks in to shut down the amp. No speaker damage. This happen one time after the amp has been on for 1/2 hour. The other time, amp shut down after 2 hours. For both times, after waiting for 5 minutes, I was able to turn on the amp again. The weather here is about 90 degrees lately and I listen at regular volume level. The hot weather probably has nothing to do with this but I thought I mention it.
5) last week, when powering up, I think I hear a "crackle" sound in addition to the "sizzle" sound. Amp did power up as usual but after about 1 hour, the amp shut down. After waiting for 5 minutes, this time the amp will NOT turn on anymore.
Questions:
- I understand that capacitors went out very often and I suspect that it's the same situation here. Anybody knows which one(s)? I have not been able to find a schematics on this forum or at the Krell web site. I also suspect that the problem is on the "start up" board and I suspect (& hope) that the amp section are fine. I have done a internal visual inspection. Nothing looks burnt or leaking.
- I have done a search on this forum but I did not find anything related to KSA-300S. Lots of info on KSA-100S though but the problems are unrelated.
Any suggestions? I plan to "dive" in and do some troubleshooting soon.
fcel,
I have a question... does the 'sizzle' sound come from the speaker or from the circuit. Not good if comes from circuit. Frankly not good if it comes from the speaker either.
Look at the top of the power supply filter capacitors (if they look like cans) to see if the tops are blistered up. They should by flat. This can indicate a damaged capacitor. (could be the sizzler)
Usually though there will be some pwr supply noise from the speaker if the pwr supply filter caps are bad.
Also look at the output transistors emitter resistors (or source resistors if its a mosfet amp) to see if they get hot or burn as this could indicate a bias problem.
You don't think the relay contacts could be corroded do you?
I have a question... does the 'sizzle' sound come from the speaker or from the circuit. Not good if comes from circuit. Frankly not good if it comes from the speaker either.
Look at the top of the power supply filter capacitors (if they look like cans) to see if the tops are blistered up. They should by flat. This can indicate a damaged capacitor. (could be the sizzler)
Usually though there will be some pwr supply noise from the speaker if the pwr supply filter caps are bad.
Also look at the output transistors emitter resistors (or source resistors if its a mosfet amp) to see if they get hot or burn as this could indicate a bias problem.
You don't think the relay contacts could be corroded do you?
And another picture showing the whole amp. I know, lousy picture - bad lighting this morning.
Some clarification:
I do have some test equipments - basic digital multimeters and scope. It's just that without a schematic, it's kind of inconvenient to do any kind of troubleshooting.
Some clarification:
I do have some test equipments - basic digital multimeters and scope. It's just that without a schematic, it's kind of inconvenient to do any kind of troubleshooting.
Attachments
Hi fcel,
If you were to look at the power switch, is it an large power carrying type or a signal switch? Are there any large relays that you can inspect the contacts on?
If the amp has a solid state switch, I would guess that the connectors are arcing.
Sorry, but the pictures are too dark for me to see much detail at the moment. I'll run them through Photoshop I see if they can be made lighter with detail.
-Chris
If you were to look at the power switch, is it an large power carrying type or a signal switch? Are there any large relays that you can inspect the contacts on?
If the amp has a solid state switch, I would guess that the connectors are arcing.
Sorry, but the pictures are too dark for me to see much detail at the moment. I'll run them through Photoshop I see if they can be made lighter with detail.
-Chris
Attached is another top view picture of the front of the amp.
1) As you can see, there are 4 small capacitors on the left side installed on a board that is mounted to the bottom chassis. Any of you know what is the function of does capacitors? Is there any possibility that they are bad?
2) On the right side facing the front, there are 4 big white resistors. Those might be fried?
I will eventually take the amp apart to troubleshoot.
1) As you can see, there are 4 small capacitors on the left side installed on a board that is mounted to the bottom chassis. Any of you know what is the function of does capacitors? Is there any possibility that they are bad?
2) On the right side facing the front, there are 4 big white resistors. Those might be fried?
I will eventually take the amp apart to troubleshoot.
Attachments
I have the world's worst camera. So, no more pictures after this one.
The attached picture shows 1 big relay and 4 small relays. They are located right below the MOV and left of the fuse. There are 4 other big relays located at the back of the amp - not shown.
Please note:
- I have avoided using the word "arcing". When the amp is working, I have only heard "sizzle" sound at turn on and then the relay kicks in and then the music comes out. No "sizzle" sound after the relay kicks in.
- there is no "sizzle" sound from the speaker.
- there is no damage to my speakers.
- no visual sign of burnt components.
- I have not inspect the internals of all the relays yet.
The attached picture shows 1 big relay and 4 small relays. They are located right below the MOV and left of the fuse. There are 4 other big relays located at the back of the amp - not shown.
Please note:
- I have avoided using the word "arcing". When the amp is working, I have only heard "sizzle" sound at turn on and then the relay kicks in and then the music comes out. No "sizzle" sound after the relay kicks in.
- there is no "sizzle" sound from the speaker.
- there is no damage to my speakers.
- no visual sign of burnt components.
- I have not inspect the internals of all the relays yet.
Attachments
My first thought was that it was the inrush resistor sizzling, but that doesn't explain the amp cutting out after a time.
I think the only approach is to take the amp apart ( mark all the parts and label the wires so you know how to re-assemble it ) and test all the components. I work without circuit diagrams, and it's more difficult, but not impossible. You could draw out the relevant part of the circuit yourself, to see how it works.
Hope this helps.
I think the only approach is to take the amp apart ( mark all the parts and label the wires so you know how to re-assemble it ) and test all the components. I work without circuit diagrams, and it's more difficult, but not impossible. You could draw out the relevant part of the circuit yourself, to see how it works.
Hope this helps.
Hi fcel,
Okay, check the contacts on the big relay. Most likely the AC power control.
Before you take the amp apart, hold a straw between your ear and the different components to see if you can locate the noise when powering up or while the noise is present. Tapping the parts sometimes will cause them to act up.
I have seen switches, relay contacts, pcb connections and snubber capacitors all make the noise you are describing. Most of the time I can narrow down the search by looking and tapping. Also, try to turn the amp on in the dark while looking inside. Small flashes of light may guide you as well.
-Chris
Okay, check the contacts on the big relay. Most likely the AC power control.
Before you take the amp apart, hold a straw between your ear and the different components to see if you can locate the noise when powering up or while the noise is present. Tapping the parts sometimes will cause them to act up.
I have seen switches, relay contacts, pcb connections and snubber capacitors all make the noise you are describing. Most of the time I can narrow down the search by looking and tapping. Also, try to turn the amp on in the dark while looking inside. Small flashes of light may guide you as well.
-Chris
While not trying to sound like a know it all, I do have close to 25 years experience at electrincs repair, and I need to point out that this guy has no real experience repairing this sort of thing. There are lethal voltages present in this amp when its powered up and possible lethal charges stored in the capacitors even after its been off for quite a while. The method of working on the amp with a straw literally broke my straw at this end AND IS VERY DANGEROUS FOR THE INEXPERIENCED.
Best bet is to get the amp to a a local experienced technician that can disassemble the amp properly and inspect the various sections for failure or damage. This amp is certainly worth a normal repair bill and were it mine it would already be on its way back to Krell for repairs and updats/upgrades. Krell provides absolute first rate repair and updating for its products. I once owned a second hand KBL preamp that developed problems and sent it off to Krell for repair. They obliged by doing the repair at no charge to me other than shipping cost.
Mark
Best bet is to get the amp to a a local experienced technician that can disassemble the amp properly and inspect the various sections for failure or damage. This amp is certainly worth a normal repair bill and were it mine it would already be on its way back to Krell for repairs and updats/upgrades. Krell provides absolute first rate repair and updating for its products. I once owned a second hand KBL preamp that developed problems and sent it off to Krell for repair. They obliged by doing the repair at no charge to me other than shipping cost.
Mark
Hi Mark,
I have in excess of 30 yrs in service, and have repaired Krell + many others. I don't know if you've noticed, but a straw is made of plastic and therefore, normally non-conductive. Not once was it recommended that fcel put hands or conductive objects into this equipment.
fcel has indicated that he would like to attempt a repair on his own amplifier. I leave it to him to determine his own limits. He has mentioned some experience with soldering so, who am I to judge his abilities.
You are correct that the amp is worth a reasonable repair bill, or shipping cost to Krell. And yes, Krell has a very good service department. It is not up to anyone, but the owner of the amp, to determine how the repair is accomplished. To that end, these questions are worth answering.
Not to pick a fight, but there is no need to be an alarmist here. By the way, I have resorted to a straw, and lack of light to successfully troubleshoot some tough repairs. I only felt foolish about these methods for not thinking of them sooner. I could have saved a lot of time!
-Chris
I have in excess of 30 yrs in service, and have repaired Krell + many others. I don't know if you've noticed, but a straw is made of plastic and therefore, normally non-conductive. Not once was it recommended that fcel put hands or conductive objects into this equipment.
fcel has indicated that he would like to attempt a repair on his own amplifier. I leave it to him to determine his own limits. He has mentioned some experience with soldering so, who am I to judge his abilities.
You are correct that the amp is worth a reasonable repair bill, or shipping cost to Krell. And yes, Krell has a very good service department. It is not up to anyone, but the owner of the amp, to determine how the repair is accomplished. To that end, these questions are worth answering.
Not to pick a fight, but there is no need to be an alarmist here. By the way, I have resorted to a straw, and lack of light to successfully troubleshoot some tough repairs. I only felt foolish about these methods for not thinking of them sooner. I could have saved a lot of time!
-Chris