I've yet to see a report on bad line input capacitors. The ones after the diode bridge connected to AC. Is it because of the low line frequency (60 Hz)?
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Re: Why don't we see bad line input capacitors?
They are made to a higher standard - they have to be to withstand the high voltages, and they are relatively low value for their size, and generally they aren't under as much electrical 'stress' as VRM caps get.
I've seen a few fail before now in TVs etc., but its always been simple age related faults rather than anything catastrophic. -
Re: Why don't we see bad line input capacitors?
True. I have seen rare few that failed early in newish TVs. Some of these big failed cap either vented it's top or can hear or feel it rattle when shaken after taken off from board.
Cheers, WizardComment
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Re: Why don't we see bad line input capacitors?
the crappy ones fail often.
ones from reputable brands you find bad are either very old or were killed by overvoltage/temp.Comment
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I have a 40 volt AC transformer that I put a bridge rectifier on, and I wanted to see the input signal and the output signal on the same screen on my scope, so I set one channel up with the test lead on one side of the input and the ground lead on the other side of the input, then I used another channel on the scope and clipped the test lead on the positive side of the output then the ground on the negative side of the output.
When I connected the transformer to power, the wire that was connected between the ground lead on the second channel and the negative side of the bridge rectifier... -
So, I have a really bizarre issue that I'm struggling to identify the cause of. Working on an 820-02020 board with some bizarre keyboard/input-source character mapping. My suspicion is a possible damaged SPI ROM (U1970), perhaps, but I'm really not sure in this case:
1. The issue is pretty weird, but when installing MacOS, I noticed my WiFi password did not work. I quickly realized the special characters (!@#$%^& etc) were not mapping correctly.
2. I noticed the keyboard layout/input-source is defaulting to JAPANESE every single time I restore the board. I am not... -
Attached schematic 🙂.
Laptop gives no signs of life. No fan and no CPU heat.
Think Engine BD4179MWV is hot on plugging in *AND* pressing the power button.
Discovered short to ground on VCC5M power delivery IC NB690GRP (5 volt line, not the high current VCC5M_PD) which is one of the ways that chip is powered. I'm puzzled.
Nothing else is warm on the board. CPU resistances are OK, 9V VSYS line is present from the BMIC. All misc and cables are disconnected.
What do you guys think happened? I've got two theories:
If the...I think ThinkEngine shorted first50.00%1I think 5V SMIC shorted first0%0I think something else happened50.00%1 -
Hi, I have some 32 bits computer motherboards that need repair, as they fail to
power on.
Here are some examples :
(N.B. "capacitors" indicated here are electrolytic capacitors located in the onboard
switching supply area).
(N.B. #2 : I could not find a 3300 microF aluminum-polymer with a higher voltage
than 6.3 V.)
1 - Motherboard #1 : this is an Asrock K7VT2 (socket A) that still works well. To put it on test
I replaced capacitors with aluminum-polymer.
3300 microF/6.3 V. x 4 replaced by 3300 microF/6.3 V. (KYOCERA... -
I am Repairing this unit. It had many problems. One major one was the power transformer being about 4-5 volts low on the main B+ line which called for 66.5 Vols after the Main Filter caps but only showing about 62 Volts. Caps and the 5 amp Diode bridge were replaced which helped slightly.
The other strange problem was the small secondary winding from the PT which supplies 18 Volts AC to the "FM FLUORESCENT DISPLAY" circuit, and the small winding that supplies 8 Volts AC to the push button grain of wheat lamps. Those voltages were down from 18 Volts to 16 volts. Which was...
Comment