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Class D Switching Power Amplifiers and Power D/A conversion

B&O Icepower 200ASC pictures.
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Old 2nd October 2017, 11:02 PM   #21
hoka is offline hoka  Netherlands
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PS: I guess you already found this:
adi final C ...-ICEPOWER 200AC Rev.D.ckt.pdf
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Old 3rd October 2017, 12:04 AM   #22
5th element is offline 5th element  United Kingdom
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I have seen that yes

With regards to why the AC modules aren't working.

If the ASC modules still work when the AC modules are plugged in then it would seem like none of the AC modules power supply inputs have shorted to ground. If they had then it would stop the ASC from working too.

It is possible that fusing, of some sort, has been included, either on the ASC or the AC board, to protect the ASC in the even of an AC failure.

Given what the AC modules are, I would expect the 4 output MOSFETs to be the most likely to break. These are some of the only active components that actually carry power, they undergo the most thermal cycles and are only heat sinked via the PCB. You could measure these and see if any of them have gone short circuit from the drain to the sink, but if they have I would expect the high voltage power supply input to the AC board to have gone short circuit. If that had happened then the ASC wouldn't work with the AC plugged in unless fusing was included.

If the output MOSFETs are fine then it's possible that the output capacitor has failed. This sits across the two outputs. If it has failed short circuit then it would short the outputs together and cause the amplifier to shut down.
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Old 3rd October 2017, 02:55 AM   #23
bwaslo is offline bwaslo  United States
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B&O Icepower 200ASC pictures.
If you get desparate, there's this as an option --
Power Amplifier Board ICEPOWER200ASC 200W Digital Audio AMP ICEpower | eBay

Looks to be genuine rather than clone, though can't be sure.
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Old 4th October 2017, 11:12 PM   #24
Eva is offline Eva  Spain
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In a class D amplifier there are essentially a few failure paths:

- Noise margin problems in switching. Oscillation at too-high frequency. Equivalent to overload. Something has changed in the circuit w.r.t. original design (I have seen this happen in old ICEpower depending on batch of parts used and temperature).
- Stability problems. Intermittent or permanent oscillation at too-low frequency. Equivalent to overload. Something has changed in the circuit too, or there was some kind of feedback from output to input.
- User dependent overload (abuse). Overheating. Either input section (signal), or output section (load). For cases not covered by limiting circuits included.
- Programmed obsolescence, like mounting main power semiconductors (subject to marked thermal cycling) directly to PCB, also subject to marked thermal cycling.
- Degradation of materials used for heat transfer. Design techniques from computer mainboard have to be borrowed with care, as these mainboards were intended to last just a bit longer than what the computers took to become obsolete, although that trend is progressively changing (theoretical silicon processing and magnetic storage limits reached).
- PSU/mains overvoltage.
- Problems related to SMD manufacturing (cold solder joints, parts failing due to thermo-mechanical stress).

When main power transistors fail, depending on the quality of the design, there may be a chain reaction of destruction and non recognizable parts, or there may be just a couple of "firewall" parts blown. Same happens for input section when it fails, the power stage may shutdown or may blow. A good design has some tolerance to powering up with faults for measuring, without blowing anything.
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Old 4th October 2017, 11:52 PM   #25
Eva is offline Eva  Spain
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Regarding PSU feedback circuit complexity:
A quick look at the pictures reveals 2 facts.
- ASC modules use a 2nd SMPS for obtaining low voltage rails, including standby rail, powered from main SMPS.
- Main SMPS is a peak current control forward converter.

These 2 facts probably imply that a dual output voltage scheme is used for main SMPS, achieved by switching something in feedback network for standby, thus the extra complexity. This approach may seem familiar from CRT TV flyback SMPS, where typically the "+B for deflection" output is switched to the "+5V logic" output for standby, to achieve idle power consumption below 1W (due to very low duty cycle, and of course regulation threshold is switched in feedback network).

Has the root cause of the failure been figured out?
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Old 5th October 2017, 12:31 AM   #26
bwaslo is offline bwaslo  United States
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Quote:
Originally Posted by Eva View Post
.....- Programmed obsolescence, like mounting main power semiconductors (subject to marked thermal cycling) directly to PCB, also subject to marked thermal cycling.
Eva, I've been running a few of these modules for about 6 years now, never unplugged. Was thinking the other day that this might be hard on them, but your comments suggest that actually might be a better way to run them. Is that correct?
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Old 6th October 2017, 12:09 AM   #27
Eva is offline Eva  Spain
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Did you say 30 years and 2+ users? 6 years is not enough time. Home living room sound is not enough power cycling in most cases, but these modules are offered for more demanding purposes. Even in the bad-BGA-solder plague a few years ago worst equipment was lasting 1~2 years in most cases.
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Old 6th October 2017, 01:13 AM   #28
bwaslo is offline bwaslo  United States
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No, just 6 years constantly powered up (and just 2 units). Wondering whether that was worse for reliability than turning them on and off each time when used.
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Old 6th October 2017, 08:44 AM   #29
Eva is offline Eva  Spain
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Each daily power cycle qualifies as a thermal cycle. But keeping modules powered on permanently consumes faster the life hours of electrolytic capacitors used for low-voltage rail decoupling. These caps may be oversized or undersized, cheapo ones rated 1000h, normal 2000h, or hi-reliability rated about 10000h, or even aluminum polymer types which in same HF circuits last like 10 times longer than standard 2000h types due to ~3 times higher current ripple capability at HF.
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Old 10th October 2017, 05:46 AM   #30
5th element is offline 5th element  United Kingdom
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No Eva the problem hasn't been fixed as I've been working on other things. The root cause of my failure would appear to be the main FET switch in the SMPS failed and took with it a number of components. I've so far replaced what I can with the help of the internet plus hokas help here.

What you are saying has maybe given me some food for thought.
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