McIntosh MS300 Music server motherboard caps

[Cohibaman]

I recently purchased a used McIntosh MS300 music server built in 2005. It's a PowerPC-based motherboard, CD-ROM, and hard drive powered by a small 65-70W switching power supply.

The power supply notoriously fails due to bad/old caps, then usually takes out the mobo. When I popped the hood, I did in fact notice a 1000uF filtering cap was bulging (later tested at 47pF), so I promptly replace all the thru-hole electrolytic caps on the power supply with Panasonics and a few Nichicons. Everything good so far.

I'm now focusing on the motherboard, which uses all surface mount caps. Any advice on whether I should I replace these as well...?

[selldoor]

Re: Music server motherboard caps

Can you test the power supply without the main connected

[Cohibaman]

Re: Music server motherboard caps

Yep, the power supply is working great both in test and connected to the server. The server is currently buttoned back up and working. I'm just looking for advice on the mobo caps. I never really worked with SMD caps so I don't know how to identify an electrolytic 100% of the time. I know, at least on some, there's scores on the top of the can for controlled venting similar to thru-holes. I'm pretty sure I know how to identify the values, but again, not 100%. As far as failed, solder joints can look corroded, cans can bulge, they can leak, etc. Looking at my mobo, I see no overt signs of bad caps, but that's not proof they aren't bad.

[stj]

Re: Music server motherboard caps

if it works, leave it.
most people cant lift surface-mount electrolytics wihout damaging the board or making the caps explode.

[Cohibaman]

Re: Music server motherboard caps

I'm comfortable with the soldering part so that's not a problem, but...it is an obsolete, unobtainium board. So I have two schools of thought on cap replacement:

1) replace the electrolytic caps that "may" be bad before they damage the board
2) do what you suggest and leave it alone since the motherboard can't be replaced

Which is a higher risk?

[Cohibaman]

Re: Music server motherboard caps

The 3 caps marked 220, 10A, 3G6 are part of the component video circuit, which is not working. S-Video works so it's not a huge deal, but are those electrolytics? Can you help me decipher the codes?

Also, the 41, 470, 16V... They look to me to be 470uF @ 16V electrolytics, correct?

[selldoor]

Re: Music server motherboard caps

Yes 220uf 10v and 470uf 16v smd electrolytic Try testing the voltage probe tab on each side

positive side is opposite the black arc

[stj]

Re: Music server motherboard caps

you can tell if they have leaked, heat one leg with your iron.
if it stinks like cat piss then it's leaked.

[selldoor]

Re: Music server motherboard caps

OFF TOPIC

Hey did you ever see a cap as sad as this one on your board - I have pinched it as an avatar

[Cohibaman]

Re: Music server motherboard caps

Hey did you ever see a cap as sad as this one on your board - I have pinched it as an avatar

...again, I don't know smd caps so please enlighten me.

[selldoor]

Re: Music server motherboard caps

Sorry I just meant it looks sad or worried and caught my imagination I have been looking for an avatar for some time. It is 10uf 16v but is probably fine. Main downfall of caps is heat so generally speaking ones on power supplies are first to go bad especially the ones near or under heatsinks. Main board ones are usually less stressed and in cooler positions

[Cohibaman]

Re: Music server motherboard caps

Sorry I just meant it looks sad or worried and caught my imagination I have been looking for an avatar for some time. It is 10uf 16v but is probably fine. Main downfall of caps is heat so generally speaking ones on power supplies are first to go bad especially the ones near or under heatsinks. Main board ones are usually less stressed and in cooler positions

Ahhh gotcha. I thought it was somehow failing and I just couldn't see it.

Completely agree, heat is a worthy adversary of many components, especially caps, and the main reason I swapped out the PS caps with 105°C Panasonic FR series.

So...the motherboard smd caps, I'm definitely replacing the 220uF's and the 470uF's in the video circuits because the component video output is dead and there's a little flicker on the S-video output. Are the Panasonic FP series the best choice or is there a better series I should use?

[selldoor]

Re: Music server motherboard caps

I dont know maybe even a bit over the top maybe FK would do - wait for someone else to chime in. One thing is to check the size of the base and position of the tabs carefully - that may limit your choice -in the through hole panasonics they dont do all sizes in all series.

[stj]

Re: Music server motherboard caps

i usually try to use smd tantalums when replacing those micro-can bastards.
i have large stocks from scap pcb's.

[Cohibaman]

Re: Music server motherboard caps

Good news & bad news

Good news:

• I was surprised that I was able to test the 9 caps in question while in circuit - they all checked out ok
• I don't have to replace them avoiding potential to brick the motherboard

Bad news:

• Now I don't know what's causing the Component Video output problem.

[mariushm]

Re: Music server motherboard caps

If (some of) the capacitors are in parallel, no matter what tool you use the results will be incorrect. Those capacitors in parallel will show as a single capacitor so the capacitance and esr will be incorrect.

Not saying the capacitors are bad, just that some of them may be. You'd have to disconnect a lead from the circuit to measure a capacitor properly unless you're absolutely sure there's no other capacitor in parallel with the capacitor you test.

[Cohibaman]

Re: Music server motherboard caps

If (some of) the capacitors are in parallel, no matter what tool you use the results will be incorrect. Those capacitors in parallel will show as a single capacitor so the capacitance and esr will be incorrect.

Not saying the capacitors are bad, just that some of them may be. You'd have to disconnect a lead from the circuit to measure a capacitor properly unless you're absolutely sure there's no other capacitor in parallel with the capacitor you test.

Agreed, but all values were right where they should be so I'm taking a small leap of faith.

[stj]

Re: Music server motherboard caps

trace the signal back from the connector and see what it passes through.

[Cohibaman]

Re: Music server motherboard caps

Unfortunately I dont have a schematic for the board, which would really come in handy.

[stj]

Re: Music server motherboard caps

lazy bastard, use a meter & your eyes!
it shouldnt take more than a few min's to trace it to the source.