AIWA CX-NH330MDK dead amp channel

[Tom41]

You might have heard about this hifi in my other topic about Dolby Pro Logic - but this is an unrelated problem. It's quite old by today's standards, seeing as it only has a 3-disc CD autochanger, twin cassette decks and a built-in Minidisc drive

Edit: Seems this unit is also known as the XR-H330MD - plenty of information for that on Google!

The speakers on this hifi are rather unusual - there's a large bass speaker hidden away at the back inside, and smaller mid-range and high-frequency speakers at the front. The bass is driven by a separate amplifier from the mid-range and high-frequency.

The hifi itself has four amplifiers - two for the left and right mid/high channels, and two for the bass left and right channels. The left bass channel seems to be dead; no signal at all coming out of it. Doesn't seem to come on, not even for a moment if I jiggle the connector around.

I've had the cover off and looked at the PCB, but can't see any dry joints or blown components. There may be bad caps, but I'd have to strip the unit right down to look at the PCB. If the rest of it isn't broken, I don't want to fix it until it is

I've also had a thought - since the bass sound is usually the same on both channels, could I connect both speakers bass channels to the working right amp output? Or would that mess up the impedance and/or blow the speakers? Or anyone got any idea how I could fix the dead channel?

[willawake]

Re: AIWA CX-NH330MDK dead amp channel

i think the guys would need some pics to help you.....

[zandrax]

Re: AIWA CX-NH330MDK dead amp channel

I've also had a thought - since the bass sound is usually the same on both channels, could I connect both speakers bass channels to the working right amp output? Or would that mess up the impedance and/or blow the speakers? Or anyone got any idea how I could fix the dead channel?

Better not connect two speakers to the same output: impedence is reduced getting nearer to a short circuit (0 Ohm), the amplifier may erogate power near its limits and this means a near continuous signal instead of an alternate one. You may damage both speakers (broken coils) and amplifier (overheat and out of range operation).

I don't know anything about component testing: my idea is swapping the right woofer with the left one, because this should help identify a driver issue from an amplifier one.

Zandrax

[Tom41]

Re: AIWA CX-NH330MDK dead amp channel

Both woofers are fine; I've tried connecting the left speaker to the right channel and got the bass sound out. I've also connected the right speaker to the left channel, and it's still dead - so definitely the amp or connectors.

Connecting both woofers to the right channel did give me sound on both of them, but I didn't persevere with that arrangement since the impedance would be all wrong.

In my opinion, the problem is occurring before the signal reaches the terminals on the back of the hifi unit - nothing to do with the speaker wires or the speaker itself.

With the side cover off, I can see most of the PCB - nothing looks burnt or damaged, and I don't see any broken/dry solder joints. I'd like to get the PCB out and look at the front, but I don't think that's possible without stripping the entire unit down and removing all components (CD player, MD unit etc)

[FIXITNOW]

Re: AIWA CX-NH330MDK dead amp channel

does it work on headphones ?
as sometime the headphone switch does get dirty and the connection for the speakers become open

[Tom41]

Re: AIWA CX-NH330MDK dead amp channel

Been away from the forums for a while, and yes, it did seem to be the headphone connection. I figured this out myself before I saw your post; while playing around with the unit, but thanks anyway

The headphone socket contains a metal strip that is pushed out of the way when the headphone plug comes in. The strip then breaks other contacts inside causing the speaker amps to be shut off. Interestingly, each amp channel seemed to have its own point on the cutoff strip that it responded to - jiggling around a pencil inside the hole got the individual channels turning off!

So all I need to do if it fails again is poke something into the headphone socket, and move it around until all the amp channels come back on.

[Krankshaft]

Re: AIWA CX-NH330MDK dead amp channel

Try spraying some Deoxit contact cleaner into the headphone jack and insert and remove a headphone plug rapidly about 10 to 15 times.

That should clear it up if it's oxidation.

Nobody who works on electronics should be without a good contact cleaner.

If that doesn't work you could always solder a jumper wire across the jack switching pins or replace the jack.

Just out of curiousity what type of headphone jack are we talking here.

A modern 1/8" one (like the one on your computer) or an old MONSTER 1/4" one ?

[Tom41]

Re: AIWA CX-NH330MDK dead amp channel

It's an older 1/4'' one; I have to use an adaptor to plug any of my modern headphones (with 1/8 jacks) into it. I don't want to disable the speaker cutoff entirely, since I occasionally like to use headphones on it and wouldn't like the noise to be blasting out of the speakers as well!