My Alesis ProLinear 720 DSP Failed

[monkey man]

I posted this over at GS, but seeing as I respect the knowledge base here so much, here's what I asked over there:

One of my 720 monitors just failed; instant "stop". No symptoms (bangs, cracks, smoke etc.).

Took it apart and it looks like what I think is a resistor, labelled RT1 on the board (not the DSP board), that's failed. It's broken in half and I couldn't see anything printed on it.

So, I took the other speaker apart and its equivalent resistor is crumbling at its edges, also no printing can be seen.

Can't create a support ticket at Alesis 'cause the product's not in the pop-up menu. Contacted Full Compass Systems in WI 'cause they say they do Alesis repairs but no luck - they don't have a service manual or parts.

Searched online for a service manual but can find nothing.

I'm hoping someone can tell me what to buy to replace these parts or at least point me to the service manual; I should be able to figure it out from there I'm hoping. Failing that, a kind soul might be willing to remove the rear panel (6 Phillips screws IIRC) and ID the part provided his aren't broken / crumbled too.

Both monitors are as-new in every respect and barely-used; it's just that one tiny part that seems to have been stressed in both units. Every other component, inside and out, looks straight-from-the-factory.

Thank you in advance for any help provided!

Hopefully one of the resident geniuses here has some insight on this...

[HCMarkus]

Carefully cut one lead on the crumbling resistor then measure its resistance with a VOM. Unless it is completely shot, it should get you in the ballpark. Then replace both. Good luck!

[monkey man]

Thank you, Brother Sir Markus!

What's a VOM? Variable Ohm Meter?

[monkey man]

OK, looked it up - Volt-Ohm-Milliammeter.

So, a multimeter, which I don't have, but that's something anyway, so thank you very much, Brother Sir Markus.

[cuttime]

Good advice, all. A VOM is an essential studio utility belt item, right next to the DeOxit and WD-40. Also, a touch of DeOxit behind the ears makes the ladies swoon.

[HCMarkus]

VOMs are not terribly expensive; great for testing cables, too.

https://www.amazon.com/KAIWEETS-Multime ... 655&sr=8-5

$11 US on amazon. Well worth the investment!

As per cuttime, +1 on DeOxit, too. You know that show "How I Met Your Mother." Need I say more?

[monkey man]

Yeah, I've sworn by DeOxit since my second AE Diploma course back in the '90s.

That stuff'll fix anything that involves a moving electrical contact.

[mikehalloran]

There are any number of VOMs on Aussie Amazon in the $15–$16 range. Any with a couple of probes and a digital readout will do.

https://www.amazon.com.au/s?k=volt+ohm+ ... e-asc-rank

So weird to see analog VOMs listed for sale… I have a few in my garage and remember using them before you could buy 'em with digital readouts but still? Those are ok for Voltage, perhaps but for measuring resistance, Yikes!

[cuttime]

Carefully cut one lead on the crumbling resistor then measure its resistance with a VOM. Unless it is completely shot, it should get you in the ballpark. Then replace both. Good luck!

You may want to go with a higher wattage resistor, as it sounds like these are overheating.

[monkey man]

My thoughts exactly, brother. The trouble is I don't know what the original is rated at.

Thank you, Mike, for your input too.

Just so I understand Sir Markus:
Do I cut one of the "stalks" and measure by rejoining the cut with the VOM or do I measure the cut stalk across to the uncut one, thus "going through" the resistor?

Also, should all power be off?

I know less than nothing about electricity; I just like to use it.

Thank you!

[HCMarkus]

My thoughts exactly, brother. The trouble is I don't know what the original is rated at.

Thank you, Mike, for your input too.

Just so I understand Sir Markus:
Do I cut one of the "stalks" and measure by rejoining the cut with the VOM or do I measure the cut stalk across to the uncut one, thus "going through" the resistor?

Also, should all power be off?

I know less than nothing about electricity; I just like to use it.

Thank you!

Power should be OFF and disconnected from AC source (Unplug from the wall). We don't want to singe any monkey fur.

Cut one of the stalks ("leads), then measure resistance thru the resistor with the VOM. If the VOM has different ranges, select the range that gets you an accurate reading.

Don't power up until the resistor has been replaced. If you want to power up for testing after the resistor is replaced but before buttoning everything up, use cautions (so as, again, not to singe any monkey fur.). After testing, disconnect power, reassemble, then re-connect power.

You'll need the VOM, some solder and a soldering iron. De-solding wick or suction device might be helpful in removing the old solder so the PC Board hole is clear, but usually not required. You can usually get the PC Board opening clear by using the soldering iron and a piece of wire.

Good luck Monkey! You can do this!

[monkey man]

Ha! Thanks Brother Sir Markus.

If the other stalk's still-connected, why do I only need to break 1 of 'em?

Is this to prevent the current from travelling through the board itself?

Thank you so much again, man.

[mikehalloran]

Ha! Thanks Brother Sir Markus.

If the other stalk's still-connected, why do I only need to break 1 of 'em?

Is this to prevent the current from travelling through the board itself?

Thank you so much again, man.

It' so that you are only measuring the one resistor. Any other resistors in parallel will be measured and included otherwise. Ohm's — not just a good idea; it's the law.

You can also unsolder one of the leads if possible but you run the risk of breaking the good resistor — and you really, really, really don't want to do that till after it's been measured.

[monkey man]

Thank you, Mike.

The bad resistor's broken in half so I figure I'd have to measure the "good" one. Only, if I snip one of the stems, how do I rejoin it if need be? Perhaps it's not the "done thing".

Just forget about it and replace both, I suppose...

[HCMarkus]

Just forget about it and replace both, I suppose...

Yes.