Altec MX6021

[momaka]

Re: Altec MX6021

Momaka, how did you know that C11 and C14 needs replacing?

Both of these caps filter the primary side auxiliary rail for the PWM IC. One of them is the "start-up" cap (most likely C11). If one or both of these go bad, the PSU may not be able to start up and make chirping or clicking sounds as it tries to start, fails, and then restarts again and again.

The problem is not unique to this power supply. Almost all PSUs that have PWM ICs on the primary side and an electrolytic startup cap can fail like this (particularly if the cap is from a known cheap/unreliable brand.)

And the symptoms of your PSU seem to agree as well:

Had a power surge from broken neutral recently.
the system can power on, kind of, just getting constant clicking noise.
unplugged everything except the the power supply, still hear the constant clicking noise, like it's from a capacitor, what does that mean usually?

... though the clicking could also come from the output capacitors, if any have failed. Just because they are not bulging doesn't mean they can't be bad. If they are indeed CapXon and Samxon like the original poster showed in page one, it might not be a bad idea to swap those as well eventually.

im getting about half the resistance on R25/26, is this normal?
Should i replace those too?

Yes, that is likely normal.
If you follow the traces on the bottom of the PCB, you will see that R25 and R26 are in parallel. If they have the same resistance printed on them, then the total resistance will be half of that.

Also, resistors tend to go higher in resistance when they fail or completely open circuit. Resistors do NOT go lower in resistance over time / with faults.

Thus, you shouldn't need to replace them.

[RJARRRPCGP]

Re: Altec MX6021

Had a power surge from broken neutral recently.

That's what I feared, when I was at 285 Clinton St. in Springfield, Vermont during April, 2016 and May, 2016. I saw the signs while looking at my UPS!

Luckily, I was safe at the time, but there were things that weren't working!

The smoke alarm wasn't working in my bedroom and there were only two of them, thus only the one in the extended part of the living room, where I had my plants, was working. (Kidde) Also, with one of the light fixtures, I thought I saw nothing for light when I put in a known working light bulb!

On the busy leg, the voltage dropped to 111V, IIRC. While the other leg was 132V! The scariest was the smoke alarm in the bedroom not working! (Looked like it was a First Alert/BRK)

Possibly all the property needed, was a new or otherwise fresh service drop from Green Mountain Power.

https://www.badcaps.net/forum/showthread.php?t=53717

[Lagodd]

Re: Altec MX6021

Hello

I am having the similar challenge of power supply failure. I don't see anything burnt. Does anyone have a diagram of the MX6021 PSU A13061 board? the measured voltage on different pin locaitons?

[sloba962]

Re: Altec MX6021

Hello,
I have a similar problem with the 6021 power supply. I want to replace it with a classic one. Is it possible to do that?

[momaka]

Re: Altec MX6021

Hello,
I have a similar problem with the 6021 power supply. I want to replace it with a classic one. Is it possible to do that?

I don't see why not. So long as you can provide the correct voltages with sufficient currents, everything should work as expected.

I think this is a dual-output power supply with a center tap, as I outlined in this post here:
https://www.badcaps.net/forum/showpo...6&postcount=57
^ That said, not sure of the voltage and current spec on the old PSU, but I imagine around or at least +/-15V for the two rails and maybe 3 Amps current max needed. See what chips and ICs the amplifier board has on it first, though. If there are any op-amps directly connected to the PSU outputs, then check the voltage rating of those op-amps to see what is the max they can take - i.e. if they are something like TL084 (which is rated for +/-18V absolute max), then you need to keep the supply voltage at least a volt or 2 lower than the absolute maximum if you don't want to blow the IC up.

Seeing that the original PSU has 25V caps on its output, I imagine the dual power supply rails are indeed at least +/-15V.

[Philippe_Quercy]

Re: Altec MX6021

Hello, could someone give me the value for R15 please ?

[zerbino]

Re: Altec MX6021

Hello, could someone give me the value for R15 please ?

SMD R473

[ramirog96]

Re: Altec MX6021

In that case, the 4 SMD resistors could be replaced with a normal 4 ohm resistor.

Thank you