Krell KSA-300S will not turn on - diyAudio
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Old 14th August 2004, 05:17 PM   #1
fcel is offline fcel  United States
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Default Krell KSA-300S will not turn on

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.
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Old 14th August 2004, 06:27 PM   #2
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Quote:
I do know how to solder.
This alone does not sound too encouraging Do you have a multimeter?

I would first of all check the PS voltages and the offset at output - obviously on the side of the o/p transitors as the relay won't kick in.

You got the sizzling sound but no accompanying smell?
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Old 14th August 2004, 06:36 PM   #3
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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?
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Old 14th August 2004, 06:59 PM   #4
anatech is offline anatech  Canada
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Hi fcel,
It really sounds like your power switch contacts have burnt. The sizzling and crackling are the contacts arcing. Some big amps use a contactor (big relay) for the actual AC switching, so check for that too.
-Chris
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Old 14th August 2004, 07:27 PM   #5
fcel is offline fcel  United States
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I have attached a picture here showing the start up control board - if it would help visualized what we're looking at.
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File Type: jpg ksa-300s 010.jpg (58.7 KB, 1267 views)
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Old 14th August 2004, 07:32 PM   #6
fcel is offline fcel  United States
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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.
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File Type: jpg ksa-300s 013.jpg (55.8 KB, 1229 views)
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Old 14th August 2004, 07:40 PM   #7
anatech is offline anatech  Canada
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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
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Old 14th August 2004, 07:41 PM   #8
fcel is offline fcel  United States
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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.
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File Type: jpg ksa-300s 009.jpg (59.0 KB, 1055 views)
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Old 14th August 2004, 07:44 PM   #9
fcel is offline fcel  United States
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Anatech,
I'll post some better pictures later.
Regarding the switch, it's those "chillet" type - where you press it to turn on. Not the rocker type.
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Old 14th August 2004, 07:45 PM   #10
anatech is offline anatech  Canada
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Hi fcel,
Still can't make out the switch. The PCB at the front looks like it is a regulator PCB, possibly with other stuff too. You may have a regular old fried power switch. Easy fix in that case.
-Chris
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