Help with intermittent Alesis RA-150

[docSanchez]

Hello everyone

I have an Alesis RA-150 that has been getting cranky over the last couple of months. At first the signal would just drop out for a split second and then come back, but now the signal drops out randomly and doesn't come back on unless I give the unit a light smack or if I crank the volume knob or input signal way up. Sometimes it is just one of the channels; sometimes they both go out. Sometimes they drop way down in volume and are distorted. I've also noticed the problems tend to occur more frequently the longer the unit has been powered on.

From what I have read, the problem is with the relay on the power supply board. Unfortunately, all my electronics experience is with tube amps and guitar pedals, so I don't know how to replace the relay.

I have the service manual for the RA-500, which has the same PCB:
Alesis RA500.pdf

The schematic is on page 16 for the power supply board (where the relay is) and page 17 shows the PCB layout (the relay being in the upper right corner)

Another things I had noticed when this problem was just beginning was that the resistors R401 and R402 had begun to burn slightly, so I replaced both of them with a 5W version instead of the stock 1W.

Finally, I have a picture of the relay itself:


If anyone could point me to a replacement relay that won't blow (I think from what I've read on the internet that a higher amp rating does the trick) that would be just the greatest.

If the relay isn't the problem, then... well, I'm going to need quite a bit more help then

Thank you all very much in advance for your assistance and advice: it is greatly appreciated.

[J M Fahey]

Read this post, it may shed some light:
TA7317 protect circuit in NAD 319 - diyAudio
Download the datasheet too, although it's not *very* informative.
http://viller.org/~cvh/nad319/ta7317p.pdf
EDIT: maybe it's not the worn/weak relay contacts , scope or put an analog meter across its coil.
If it loses power even momentarily it *has* to disconnect, just doing its job.

[Enzo]

That 7317 is used in Samson and HArtke products. The chip is rarely at fault, and if both chanels are cutting out, it is EXTREMELY unlikey that two relays have the exact same intermittant problem that occurs at the same time.

As JM suggests, monitor the relay coil voltage. If it is dropping out then the relay is just doing its job. And we then find out what is dropping it.

First, I'd replace the two input related caps, C413,414 on your print. And C416 is suspect.

You can also apply a signal and monitor the amp output bus on the amp side of the relay. If the signal remains there when the relay drops out, then it would seem that the amp was OK. If the signal disappears even there, then teh relay may be being controlled for a legit reason.

[docSanchez]

I can take a look at the relay coil voltage tomorrow, but the caps you mentioned, C413, C414, and C416 all appear to be in perfect condition. Now I know things aren't always as they seem, but these caps don't have the slightest deformation or marking.

[J M Fahey]

I wish it were that simple.
Only the grossest problems (burning/leaking/exploding/cracking) offer visual clues, for the other 99% we have to use test instruments.
Sometimes not even them show much, and we just replace the part for a known good one.

[Enzo]

They don't want every little peak dropping the amp out, so those caps slow down the reaction, if a peak is over before it can fully charge one of those caps, then the 7317 can;t trigger. If one of those caps dries out inside, no more delay.

[docSanchez]

Okay, I'm going to measure the voltage on both sides of the relay today, but (forgive me if this is a newb question) why do you keep referring to the part as a 7317?

[J M Fahey]

why do you keep referring to the part as a 7317?

Because ths Integrated Circuit that controls that relay *is* a TA7317P , called affectionately 7317 by his friends.
Also, what we need to know is whether the voltage across the relay coil (as in: "black probe to the lower pin, red probe to the upper pin") dissappears , even if momentarily, at the same time that the sound mutes or chirps.A digital meter may be too slow to catch that, so I suggested (in decreasing order) a scope, an analog (needle) multimeter or a humble 4k7 resistor in series with a LED (the poor man's scope), from the upper to the lower leg, the LED arrow or flat side pointing down, which will glow steadily and blink dark when the relay gets unpowered.
As you see, the current theory is that the relay works fine, the problem lies in its driving circuit.
Of course we may be wrong, this ckeck will test that.
Good luck.
PS: by up , down, etc. I refer to "as drawn"; the actual part on the board may point anywhere.

[docSanchez]

Ok, I think I can do that. Just have to wait until this afternoon.
However, I have to question whether the problem would be this early on in the circuit; when the signal drops out it usually is only one channel, and it doesn't necessarily drop dead; sometimes it just weakens and/or distorts. Also, it can be either channel. Neither channel falls out more than the other. Would the power supply really be the problem here? How could interrupted power drop one channel but not the other; except it's not just a one channel; it can be either channel; equal chances.

I don't mean to question anybody's knowledge or expertise here (my knowledge and expertise is meek and feeble, and I can humbly admit so) I just want to understand why/how this could be the problem.

[J M Fahey]

Hi Doc.
Rest assured that nobody is a Wizard here, with supernatural powers.
We all look at the circuit , which is a functional unit, and knowing what it *should* do, analyze why it does not. Since we can't see electricity, we rely on measurements.
If suspicions get confirmed, we move along that way; if not, we consider other possibilities.
You started suspecting the relay itself, some answers followed that path, now some of us are suspecting the circuit that drives that relay, and so on.

when the signal drops out it usually is only one channel, and it doesn't necessarily drop dead; sometimes it just weakens and/or distorts. Also, it can be either channel.

This is new info, at least for me, and changes things.
There is one relay controlling both channels, it's difficult to imagine it cutting once one channel only, then the other at some other moment.
You might even have a problem as stupid as a dirty/worn volume pot, or some poor contact.
Anyway, no problem is stupid if it makes you waste time.
Really you should try to get a scope, even carrying your amplifier somewhere.
In my early days I did just that, carrying stuff to the University Lab, at odd hours, until I could buy a surplus military scope, probably WWII vintage. A new one was absolutely out of the question, given my meager funds.
The next best option is an audio probe: a .047uFx630V in series with a 1M audio taper pot, into an LM386 simple battery powered amplifier, driving headphones.This with a 1M shielded cable, with crocodile clips, to "listen" anywhere in your amp.
It will let you trace an audio signal along the circuit, until it fades, distorts, chirps, whatever.
EDIT: how often does the sound cut now? Minutes?

[docSanchez]

I will look into building that audio probe, as I have to make an electronics order for a transformer today anyway. The sound lasts about 15 minutes, and then it starts running into problems. The longer I've run it after that, the more frequently it drops out. At its worst it drops out every 2-3 seconds, at which point I exasperatedly throw my arms up in the air and shut the unit off.

[J M Fahey]

It's *good* that it drops every 2-3 seconds !!
The most unnerving problems are intermittent ones, specially when they happen absolutely at random, and never when you are paying attention.
Even worse when the thing works all the time at the lab, and fails constantly at the client's house.
I've chased ghosts for ages, and when my clients ask , sometimes "tell me the truth ... *can* you repair it?", the answer often is: "I can only repair defects I can see" (or at least try to).
I also tell them, to their horror, that I much prefer the type "it smokes, sparks, buzzes ... etc." to: "weelll, it *woooorks* ... can't say it doesn't , buuuttt ........ "

[docSanchez]

Hooray!...?
Yeah, that is a good point. At least we have some solid symptoms to work with.

[docSanchez]

Okay, I still haven't done any of the tests you folks have suggested (shame on me; wasting your valuable assistance just because I am so lazy ... BUT! From looking at the schematics, and what I have read on the internet, it does seem consistent that something is wrong with the relay itself. If you look at the schematic, the each output (the L and R) are come directly out from the relay. From what I hear, something in the mechanics of the switching mechanism in the relay wears down when the relay is brought into play when the amp is being pushed (which I have definitely pushed it. I just... I need loud...) so I am going to try everything you guys have mentioned (that is, the things I am capable of) now that I have the unit cracked open on my desk; and if that fails I'll go with what I've read elsewhere: replace the relay with a higher amperage one. (Currently a 5A relay; upgrade to an 8A I think somebody did and it fixed their problems? Here is a link to all that business: Amp cuts out after a while - FixYa

Again... thanks for the help. This is all over my head, but I don't want to just fix it; I want to know the 'why' and actually learn something from this.

[kevwright]

I have an RA 150 and a RA 300 and both amps are giving a similar problem.
The 300 is the older of the two and this sometimes cuts out either channel. If a hit the amp, it sometimes comes back on. Sometimes its just distorted in one channel. Or if I crank the volume up for a split second, this brings the channel back.
The 150 only has this problem in the left side. Will just cut off randomly and even a light tap on the bass speaker cone (I know, shouldn't really do it) will bring the channel back. Or a firm slap on the amp itself.
Must be a common problem with these Alesis amps. Will look at the relays and report back.
K