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Fixing Onix OA21 amp

S

smintel

Member
So I've got an Onix OA21 amp - its started playing up - you turn it on, sound plays for 2 secs then cuts out. Turn it off, sound comes back for 2 secs then cuts out. Repeat.

I'm guessing this is a capacitor issue - does that sound likely? I opened it up, the capacitors do not look obviously blown. Would it be the four big ones or something else?

And if it is these, any idea where I can get replacements from? (I'm in UK)
 
Though it may sound simple from your description, it needs far more fault finding to find out what is going on and what voltages are going missing etc. It sounds to be upstream of the capacitors or if it has a protection mode then it's going into that. Simply changing things as "it may be" what's wrong with it is more likely to end up with more faults than there is now.....leave it to the professionals to sort out if you are not absolutely sure what you are doing. PS: I doubt it's the capacitors!
 
Now I have has a chance to look at a photo of the innards, then try a gentle tap on each relay in turn when the amplifier is on and see if the sound comes back. You may be lucky -but I have found enclosed relays that don’t handle a lot of current don’t fail very often. Be careful not to disturb or touch anything else as it’s easily done if you are not familiar with electronics. Be aware though that tapping a component on a circuit board can also reveal dry joints, so it may not be the relays but should help in narrowing things down.
 
Thanks for your advice on this. So to update, I took the case off to try the relay tapping as suggested. Plugged everything in and turned the power on. There was an alarming visible spark and a loud crackle sound - thought I'd blown it for sure - but amazingly everything now seems to be working fine on all inputs.
So not sure what the issue was, maybe I have a flaky component rather than a failed one. I'll put the case back on and hope for the best.
 
smintel said:
Thanks for your advice on this. So to update, I took the case off to try the relay tapping as suggested. Plugged everything in and turned the power on. There was an alarming visible spark and a loud crackle sound - thought I'd blown it for sure - but amazingly everything now seems to be working fine on all inputs.
So not sure what the issue was, maybe I have a flaky component rather than a failed one. I'll put the case back on and hope for the best.
Click to expand...

That doesn't sound very safe. If I were you, I'd arrange for it to go to a competent repairer before using it again.
 
Make sure the power connector from the mains transformer (big round coil) is properly seated on the connector on the pcb. Do this with it not plugged in to the mains! The wires to that connector are very stiff and can pull the connector slightly off. Just make sure it’s firmly in place.

If there’s still an issue I echo the advice above to send to a competent repair person to diagnose
 
Definitely mains related, as I suspected from your original description which is why I said to leave it to the professionals. From now on, be VERY careful, mains electricity kills hundreds of people a year just in this country and a shock is not nice (as anyone who has worked on electrical and electronic equipment professionally will have had one or more at some time) will tell you. As I said in my first post on the matter "leave it to the professionals to sort out if you are not absolutely sure what you are doing" and unfortunately you have found out the pitfalls of having a go. Fortunately tapping the relays has narrowed down to where the fault is and no harm done up to now - and if it is the connectors it possibly won't be long until it happens again. If sparking has been involved, it tends to damage connector pins.
I'm not saying to anyone don't have a look, but accept your limitations especially if mains electricity is involved. "I'll just have a go" ends up with many people injured each year - not just with electronics. Look up the numbers of people electrocuted doing DIY for example.....
PS: This post is not intended as having a go personally, but more as a general warning to all the others on the forum.
 
Should have added this to my last post - sorry having a brain fog day! Now you know where the problem lies and it's probably just a faulty connector and the problem is likely to recur (The pins of that type of connector get dirty along with the spring contact in the socket which is probably why you have the problem and the spark!), you may want to have a think about wiring the socket out completely. I have done this on many of these types of connectors over the years. If you are handy with a soldering iron, don't mint the amp not being original - and the wires are long enough, simply cut the wire at the socket as close as you can to it and solder directly to the pins on the PCB. Obviously you should insulate the pins to prevent shorts. The problem will then be sorted for good (unless something else goes wrong!). It goes without saying that I advise that you double check that the amp is disconnected from the mains before doing anything! If you are not confident in doing this, any competent repair shop should be able to do the job for you at a reasonable cost (about 1/2 hours labour I would think)
 
Al M said:
Should have added this to my last post - sorry having a brain fog day! Now you know where the problem lies and it's probably just a faulty connector and the problem is likely to recur (The pins of that type of connector get dirty along with the spring contact in the socket which is probably why you have the problem and the spark!), you may want to have a think about wiring the socket out completely. I have done this on many of these types of connectors over the years. If you are handy with a soldering iron, don't mint the amp not being original - and the wires are long enough, simply cut the wire at the socket as close as you can to it and solder directly to the pins on the PCB. Obviously you should insulate the pins to prevent shorts. The problem will then be sorted for good (unless something else goes wrong!). It goes without saying that I advise that you double check that the amp is disconnected from the mains before doing anything! If you are not confident in doing this, any competent repair shop should be able to do the job for you at a reasonable cost (about 1/2 hours labour I would think)
Click to expand...

If OP is referring to the transformer as a big round coil, no disrespect to him but I do not think we should be giving any advice or suggestions on DIY work! Just send it to someone that is competent (repair shop or friend with plenty of DIY knowledge and experience at the very least), it's far safer.
 
It's up to the OP to decide wether or not he has the abilities to do this sort of work - none of the rest of us have the right to comment. The advice given has enough warnings as to not to do it if he was not confident. After all, it's remaking a few connections and this is a DIY forum. To put this in context, I know people who try to build valve amps from a kit without really knowing what the parts are! Everyone has to start somewhere and I'm sure the OP has learned a few valuable lessons from this.
 
James Evans, great insight about re-seating the PT header. F'ing Onix!

OP, send it off for a full service, unfortunately it's a time consuming PITA to work on as it's a cool looking but stupid assembly, it is however, a nice sounding small, powerful, snappy, clear and transparent amp worth the effort to save. Maybe you can find a hobbyist who will do it for a reasonable cost just for the challenge. I recently did my OA21 through and through, no monkey business just like for like, new trimmers as they drifted like crazy, the critical thing was the relays, they worked fine but replacing after 35ys was a revelation, so much so I posted on it. I used Nichicon KL (low leakage) e-caps in any coupling position on the PCB and the phono, with no schematic I decided that was any connection that didn't go to ground, I'm pretty sure it made at least the phono quieter.

Now the other revelation: I've owned this new since the mid '80s, initially used it with Kimber 8TC, hot shit cable back then, few years after buying it got relegated to kitchen duty with very long runs of cheap flat IIRC Audioquest, then storage for a decade. After the recap I of course noticed it didn't use an output coil, so, no more exotic cables (8TC yikes!) but money's tight and I have several coils of Canare and that's what I used. I don't consider Canare exotic, just a reliable working man's cable that won't give problems.

Recently I picked up a used set of first version Mission 751s, minty and cheap, worked nice with the tuned up Onix, well enough that I got the optimization bug, so I took the NACA5 off my Naim, and holy mother of Jesus! The few things I never liked about the Onix if not disappeared lessened a lot, I always thought it lacked a little body, Fender bass lacked the proper growl and grunt Naim gave it, always found the Onix super transparent but thin and cold, lacking warmth and body w/ respect to Naim, the NACA5 settled most that, the treble with the Missions was a touch sharp too and also went away. Much more balanced and proper sound.

My test that things aren't my imagination is if I find myself turning it up more and more and getting a Jones for well recorded albums. That happened after the relays and now with the NACA5. Next day I ordered some Linn K20, which is on it now.

If you own an old OA-21 change the relays and use low capacitance, high inductance cable.

Further FYI: Triangle Speakers (French?) offer a very cheap cable called Opera built like K20, I emailed them and they sent me the specs pasted below, seems perfect for Naim, Exposure, Onix... You can get it at Audiophonics in France: https://www.audiophonics.fr/en/

For Opera 2.5mm2:
Capacitance : 24.579 pf/m
Inductance : 1.222 uH/m

For Triangle Opera 4mm2:
Capacitance : 27.245 pf/m
Inductance : 1.195 uH/m
 
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I never knew it had a lifetime warranty, so I guess I can't feel screwed, not that it ever broke. What they really missed was not telling customers to use a low capacitance high impedance cable, sheesh, 35ys with the wrong cable :(
 
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