MS275 Power-up fault
MS275 Power-up fault
Hi everyone! I have two ms275's sourced from eBay and after performing cap upgrade/replacement one of them flashes the OVR light for a second or two before powering up and functioning, as far as i can tell, normally. I can post some more specific info but I just wanted to see if this sounds like a known issue right off the top. The momentary overload condition is longest at the initial power up after connecting the mains and subsequent power cycles cause just a quick flash. The OVR condition always precedes the internal LEDs and main power LED.
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trickyricky
- Posts: 1653
- Joined: Sun May 06, 2012 8:01 am
Re: MS275 Power-up fault
Normal,
Its like JL's they turn on with the low ohm LED on then it switches to the green "POWER" LED.
Its like JL's they turn on with the low ohm LED on then it switches to the green "POWER" LED.
Re: MS275 Power-up fault
Thank you!
Let me elaborate a little bit. When I decided to get an MS amp I just had to get a 275 model. Back in high school I couldn't afford one myself, but a good friend of mine had one and so I was right along for the ride with this amp through several configurations and a few cars and fell in love with it. We were not kind to this animal but despite numerous thermal shutdowns and general mishaps it never surrendered. I don't think we opened it more than twice just to stare at it.
So the first amp I obtained is a white model with a rev/G board and I pulled the caps upon receiving it. I did not apply power to the unit prior to this. The area under the coupling caps was dry and shiny despite expectations. The cap job encompassed those and the rail supply caps. Both groups were upgraded in capacitance with new units registering 6800uf on the couplers and 15,000uf on the rail supplies. That decision was based more on an "it's not going to hurt" viewpoint rather than thinking it would help anything.
Now, at this point I had not read nearly as much as I have now on this subject. The driving force behind all the reseach started but did not end with pulling some vias in the process of uninstalling the rail supply caps. After my heart attack I read up and landed on some nice press-ins from ebay which worked very well for me. However, not knowing better at the time, I repaired only the vias that the trace material had fallen off and did not inspect the others for less obvious damage.
When it was time to power the amp up I connected it to my bench supply project rats nest disaster that supplies 52A @12VDC. It's perfectly trustworthy, just a bit cobbled together at the time you see? At the time I meant to let it sit for a moment before applying current to the remote input but just mindlessly attached it pretty much immediately after switching the power supply on instead. I don't know why I was going to wait. I doubt it would have made a difference. But anyway, if I had any music going on in the background as I regularly do I may have missed it entirely. An ever so faint sizzle that immediately drew my attention to the leds in time to see the OVR led alight before the unit powered up successfully. There was no other indication of the event. No smells or light or visibly burned circuitry. The ominous sizzle has not recurred after a few times of restarting the amp whether power cycling in a single testing session or after several days of full disconnection. The OVR condition is longer on initial startup after being disconnected than when power cycling however.
Fast forward a month or so and I got my hands on a gray rev/F model also from ebay and again went about overhauling the electrolytics straight away. These were leaking as you would suspect. Now, this time I knew that replacing the rail caps was almost certainly not necessary but had also decided I would use this as a chance to see for myself about the SQ merits of opamp upgrades for the hell of it. Again the guiding thought being that the worst case scenario was that they would have no effect whatsoever. So in the interest of keeping all else equal I did the rail caps on this unit too.
This unit has powered up and performed flawlessly just as I recall. I am currently running it with 20A @14.4VDC and have powered up the white model on this supply too with the same OVR condition at startup. DC offset tests revealed nothing alarming at .004/.008 on the white rev/g model and .005/.015 for the gray rev/f model. The reason I mentioned possibly overlooking a bad via on the rail caps is I'm wondering if I heard a severely damaged via burning out? What would an amp do with one rail cap disconnected? Would it function at all? If that would prevent it from functioning at all I can put off a full disassemble for the sole purpose of checking those areas. I have refrained from further testing due to fear of further more serious damage to the amp.
All that being said, what I'm looking to get is some info on maybe some good places to start looking for a problem with a multimeter since I have a properly functioning unit for comparison, or if this condition rings a bell with anyone.
@trickyricky- Have you personally seen this on one or multiple MS series amps specifically? I never have. If so do you recall what color the amp or amps were?
Let me elaborate a little bit. When I decided to get an MS amp I just had to get a 275 model. Back in high school I couldn't afford one myself, but a good friend of mine had one and so I was right along for the ride with this amp through several configurations and a few cars and fell in love with it. We were not kind to this animal but despite numerous thermal shutdowns and general mishaps it never surrendered. I don't think we opened it more than twice just to stare at it.
So the first amp I obtained is a white model with a rev/G board and I pulled the caps upon receiving it. I did not apply power to the unit prior to this. The area under the coupling caps was dry and shiny despite expectations. The cap job encompassed those and the rail supply caps. Both groups were upgraded in capacitance with new units registering 6800uf on the couplers and 15,000uf on the rail supplies. That decision was based more on an "it's not going to hurt" viewpoint rather than thinking it would help anything.
Now, at this point I had not read nearly as much as I have now on this subject. The driving force behind all the reseach started but did not end with pulling some vias in the process of uninstalling the rail supply caps. After my heart attack I read up and landed on some nice press-ins from ebay which worked very well for me. However, not knowing better at the time, I repaired only the vias that the trace material had fallen off and did not inspect the others for less obvious damage.
When it was time to power the amp up I connected it to my bench supply project rats nest disaster that supplies 52A @12VDC. It's perfectly trustworthy, just a bit cobbled together at the time you see? At the time I meant to let it sit for a moment before applying current to the remote input but just mindlessly attached it pretty much immediately after switching the power supply on instead. I don't know why I was going to wait. I doubt it would have made a difference. But anyway, if I had any music going on in the background as I regularly do I may have missed it entirely. An ever so faint sizzle that immediately drew my attention to the leds in time to see the OVR led alight before the unit powered up successfully. There was no other indication of the event. No smells or light or visibly burned circuitry. The ominous sizzle has not recurred after a few times of restarting the amp whether power cycling in a single testing session or after several days of full disconnection. The OVR condition is longer on initial startup after being disconnected than when power cycling however.
Fast forward a month or so and I got my hands on a gray rev/F model also from ebay and again went about overhauling the electrolytics straight away. These were leaking as you would suspect. Now, this time I knew that replacing the rail caps was almost certainly not necessary but had also decided I would use this as a chance to see for myself about the SQ merits of opamp upgrades for the hell of it. Again the guiding thought being that the worst case scenario was that they would have no effect whatsoever. So in the interest of keeping all else equal I did the rail caps on this unit too.
This unit has powered up and performed flawlessly just as I recall. I am currently running it with 20A @14.4VDC and have powered up the white model on this supply too with the same OVR condition at startup. DC offset tests revealed nothing alarming at .004/.008 on the white rev/g model and .005/.015 for the gray rev/f model. The reason I mentioned possibly overlooking a bad via on the rail caps is I'm wondering if I heard a severely damaged via burning out? What would an amp do with one rail cap disconnected? Would it function at all? If that would prevent it from functioning at all I can put off a full disassemble for the sole purpose of checking those areas. I have refrained from further testing due to fear of further more serious damage to the amp.
All that being said, what I'm looking to get is some info on maybe some good places to start looking for a problem with a multimeter since I have a properly functioning unit for comparison, or if this condition rings a bell with anyone.
@trickyricky- Have you personally seen this on one or multiple MS series amps specifically? I never have. If so do you recall what color the amp or amps were?
-
trickyricky
- Posts: 1653
- Joined: Sun May 06, 2012 8:01 am
Re: MS275 Power-up fault
I have had a few MS275 but that's it, never lucky enough to find an affordable (LOL) MS2250.
If any amplifier upon power up (remote or without remote) pull excessive current, more than 5amps then something is wrong. Most AB channels pull around .75a per channel so if you have two it would be around 1.5a on the B+.
My MS275 did that upon power up, was on overload LED then when straight to the power up "Green" LED. Its normal, if it turned on immediately it would cause turn on and off thumps. So its a slight delay (may be a second or two).
You would probably have to remove the board in order to test those solder pads on the caps.
If any amplifier upon power up (remote or without remote) pull excessive current, more than 5amps then something is wrong. Most AB channels pull around .75a per channel so if you have two it would be around 1.5a on the B+.
My MS275 did that upon power up, was on overload LED then when straight to the power up "Green" LED. Its normal, if it turned on immediately it would cause turn on and off thumps. So its a slight delay (may be a second or two).
You would probably have to remove the board in order to test those solder pads on the caps.