McIntosh system : sporadic operation

[matt1710]

I have a 2000 Legacy GT-B E-Tune with McIntosh : HU, under-seat amp and 6 disc changer in the boot. The problem is this : the sound system only sporadically produces sound. It has done this on and off for months, however it was generally more 'on' than it was 'off' so I lived with it. However now it's the reverse and it's hacking me off.

The HU lights up fine, and controls the stacker, switches stations etc - but no sound is produced. There is almost never sound when I start from cold, and sometimes, after driving around, the sound will just come on - it seems to "fade in" over a few seconds rather than just instantaneously achieving the set volume. Sometimes it switches off again after a few seconds - other times it stays on for the rest of the trip. The strangest thing is that until a few weeks ago, I discovered that hitting a bump (even a lane marker bump on the m.way) with the left front wheel would generally produce sound from the ICE. Now that trick rarely works. :-\

I assume there is an issue with the ICE wiring somewhere, or perhaps even inside either the HU or the amp itself. Could it be a faulty/loose component in the HU or amp - or does it sound more like a loose wiring connection? Not really sure where to start - and who to ask for assistance. Does it sound like a "needle in the haystack" type problem? Any recommendations as to who to contact? ???

I'm reluctant to replace the HU as I understand that will make the stacker and amp worthless, AND I'll have to get the entire thing re-wired to by-pass the amp.

Matt

[Scoobydoo]

Can't help you much with your current problem, but if you do decide to go for a new headunit, you can use my tutorial to help you with the wiring. And yes it will render the Macintosh amp and stacker useless.

http://www.clubsub.org.nz/forum/index.php/topic,766.0.html

[matt1710]

Thanks for that - have had a read through the post and will certainly follow that if I can't sort the problem. Would seem a shame to essentially trash the amp and stacker though. I note that someone in your post just cut the connector off the HU end of the cable that ran from the amp, and attached RCAs - which plugged into the new HU. Excuse my ignorance, but doesn't this mean that the new HU would be driving the speakers through the amp?

[Scoobydoo]

Yeah thats right, but obviously he is very competent. That would've involved chopping the DIN connection off, and soldering RCA barrels onto the bare wires.

That can be done I guess. But I don't think the amp is much better or more powerful than most modern headunits anyway, and certainly not as good as modern amps.

[matt1710]

Hmm - sounds like I'll have to investigate how tricky an RCA is to solder onto a bare wire. I reasonably proficient with a soldering iron - but maybe RCAs are particularly difficult. Is it possible to get a DIN loom with RCAs on the ends? That way I'd just have to determine the appropriate inputs on the new HU, for each RCA plug. Actually, I didn't even know that car stereos had RCA inputs.

It's not so much that I believe the amp and stacker are great - it's just that I don't want to lose use of them if I can help it. If I was to install a new HU and use the existing amp-HU cable (equipped with RCAs), am I right in thinking that there's no chance of the new HU driving the stacker?

[Scoobydoo]

You are right in thinking that.

[Guest]

look on trademe for a replacement McIntosh system?

[matt1710]

Am actually on to the second McIntosh HU and amp...still have the old gear - maybe I should try the old HU in it again. Problem is, I'm not sure where the issue is : inside the HU, in the cabling, in the amp.... If anyone has any bright ideas of how to identify/narrow down where the issue is, I'm all ears!!

[Scoobydoo]

Short of replacing both the amp and the cabling, it's pretty difficult to find problems like that

[Guest]

The McIntosh amp as part of that system is actually quite a competent wee amp which boasts some very nice THD figures.

It has a couple of limitations in that it accepts four channel line level input and has a equaliser in it that generates a subwoofer channel out of the four inputs and it isn't hugely powerful (70w into 4 ohms and less then that into 8 ohms (which is what the factory speakers are).

I recently fitted a Pioneer headunit instead of the McIntosh as I needed more features and I've soldered RCA's onto the DIN cable that leads to the amp. It wasn't very hard to do at all. I grabbed an RCA cable, cut it and soldered cable to cable rather then trying to fit the RCA's directly to the DIN cable.

To be honest though, I have developed a whine... I'm not sure whether it is an earthing problem or a cabling problem at this stage... I really need to pull the headunit out and conduct an experiment or two to figure it out but it was fine to start with.

As for your problem, I suspect a cabling problem. While the stereo is not producing any sound, is the amp on (i.e. is it slightly warm?). If not, I'd suspect a power supply problem or a DIN cable problem. If it is warm (or at least not freezing) I'd look at the white plug on the AMP that leads off to the speakers.

[matt1710]

Hey SpotMe

Thanks for the helpful post. Good idea re the RCA cable cutting - meaning only a 'wire-wire' solder instead of 'wire into RCA'.

I'll check to see if the amp is warm while the HU is on but not producing sound. I've got a spare amp - maybe that can form part of the testing.

One other thing - the cable linking the HU to the stacker actually has a soldered joint in it - could that be contributing? I get the 'no sound' thing regardless of which input I'm selecting - ie radio, CD, stacker.The cable was completely cut in half at one stage but the two ends were soldered together.

[Guest]

Hmm, yep, if that DIN cable has been cut and put back together it is a probable cause!

[matt1710]

Oh - I figured it wouldn't come into play unless using the stacker - not that I know much about auto electrics! Isn't it a CeNET cable - it's the one with the square plug. I guess if I unplug the HU-stacker cable (from the HU) and the problem disappears, I'll know for certain that it was the problem. From what I recall however, I had the 'no sound' problem with the old HU/amp combo - and at that time I didn't have the stacker, nor the soldered cable.

[Guest]

Oh sorry, the CeNET cable to the stacker... I didn't read your post correctly. I wouldn't have thought that'd cause a problem, no.

[matt1710]

Went in to Driving Sound today to buy a P-Bus iPod adapter (he said they're $200 - I figured it would just be a cable!) and mentioned the 'no sound' issue - that is sometimes fixed by hitting a bump with the left front wheel. He suggested that it might be the left front speaker shorting (or did he say "going to ground"??). Does that sound plausible? If so, seems that I'd better remove the door trim and check the speaker connections...

[Guest]

that could very well be the reason, if your cable earths it will stop the sound

-smurff

[matt1710]

Hmmm - how the hell to find it though!! I guess I'll start at the speaker in the front left door - then check the rear left door. I have a multimeter - can that help me in anyway? If I'm testing a section of wiring - I assume I'm looking for a break in circuit - so I can use the continuity tester feature??

[Guest]

take the door panel off, turn the stereo on, move the speaker, see if it cuts out?

-smurff

[matt1710]

Yeah, I figured that'd be where to start - mind you it's pretty much permanently off nowadays and the bumps turn it on - and then off again sometimes. I was just fearful that the short could be in a length of cable somewhere rather than at a connection - hence my question re testing with a multimeter. I guess it's more likely to be at a connection than in some random stretch of cable - unless there was a chaffing/jamming point.

[Scoobydoo]

Yeah probably at the speaker, a solder could've become dry and come loose.

And yeah the p-bus ipod adaptor is $200... sux I know, but thats for the proper job that will charge, but just be sure that it will be compatible with your headunit.

There is another much cheaper option, which is to get one of these: http://www.trademe.co.nz/Browse/Listing.aspx?id=306655600 then a 3.5mm --> RCA cable.

[matt1710]

Thanks for that! I'm happy to spring for that cable - the p_bus cable was too pricey, especially considering I plan on upgrading the car soon.