• Please note that there are a few updates and clarifications made in the Audiokarma Rules, mostly relating to advertising and the addition of the new "Paying it Forward" & "Giving back" forums in the AudioKarma Audio Marketplace section.

McIntosh MX134 problem after years of great dependabilty.

R

raydium

New Member
Hi All

Hopefully someone can point me in the right direction. I have an older MX134 , I got it years ago along with a number of other McIntosh Components. I have had very good luck with them all with no issues up to now. But nothing lasts forever and now I have a problem with the MX134. Luckily it still works for the most part and sounds great. The problem that is starting to develop is when I turn it on from standby after it sits a while, the remote will not work and the front volume control seems to be erratic. I found that if I turn the power off from the front and let it sit for a while and then turn it back on it will come on and go into standby like normal. Then I can use the remote to power it on and everything is normal until the next day.
I guess I was wondering if this is a problem that anyone is familiar with? I am guessing it is a Chip or circuit component going bad. I am fairly good at circuit repair and if it was a known issue with a known bad part I would attempt to fix it myself. If not I would send it for repair somewhere. So does this sound familiar and if not where is a good repair center that I can send it to. I am in Ohio.
Thanks for anyone's help.
Ray
 
Register to hide this ad
Hello !

I never get this problem on all MX134 I receive for repair or complete check up before to be sold .....

One question : does the unit make that each time and the same way ? It never work normally after a long period of time without use ?

In the last one I get for repair for erratic function I have replaced all the rotary switches with bad contacts all the time but regarding your trouble it is difficult to say from here (France) :scratch2:

Sorry ! I hope that another MCINTOSH guy will be able to help you :yes:
 
Actually happen to have an MX134 in the shop right now, with quite a few issues greater than yours, but some of them do overlap.

The erratic volume control is usually an issue with the encoder, which BTW are used for most of the front panel controls. The encoder is a mechanical switch arrangement that when the knob is rotated, sends pulses to the controller circuits, which in turn operate the various settings electronically. Unfortunately, there appears to have been a vendor problem with these parts and they are prone to develop erratic contacts. This adds noise to the normal pulses, confusing the processor with the random extraneous "data". The faulty encoders need to be replaced. When the unit is working properly, check all the rotary controls on the front panel-- if one is going bad, often the others aren't far behind. I generally change them all while I have the unit apart if any are showing signs of erratic operation. They aren't terribly expensive, but they are mounted on a double-sided PC board, so they are sometimes tricky to get unsoldered.

However, they don't explain anything with your startup/remote issue. First suspect there is the "Main Micro Flash" IC, IC14 in an MX134, part # 133-522 (with the current firmware already pre-programmed). There are quite a number of IC's in the control system that could cause these kind of glitches, but I've found most of the time changing this IC will fix things.

Lastly, an odd little mechanical thing that can be overlooked, which is one (or more) of the front panel pushbuttons getting mechanically or electrically stuck, often from having someone spill something on the panel or grossly excessive use of glass cleaner that migrates into the switch. If any of those switches get stuck closed, it can prevent any additional operation of the unit-- especially the red power button.

This is a seriously complex component, so you may wish to check with the Mac factory for an experienced tech in your area, but if you want to give it a go yourself, the above things are where I'd start.
 
Thanks for both of your replies.

I will go through and check all the rotary and mechanical switches and see if I see any thing obvious, I have had the unit for a long time so if the rotary controls are a known problem I suspect they probably need replaced anyway. My problem always seems to occur after setting in standby over night and always powering it completely off, wait a few minutes and back on seems to fix it. I left it completely powered off last night and am curious to see if it acts different tonight. Either way something is wrong. I agree with you that it sound's like an IC going bad. I used to be an electronic repair tech when I was younger and worked on many double sided boards, but I was younger, had good equipment and better eyesight. If I tried it now I would probably wind up damaging the board. I make the front control checks but unless I get lucky I suspect I will be sending it to a service center.

Thanks for your help.
Ray
 
Classic_CJ said:
The erratic volume control is usually an issue with the encoder, which BTW are used for most of the front panel controls. The encoder is a mechanical switch arrangement that when the knob is rotated, sends pulses to the controller circuits, which in turn operate the various settings electronically. Unfortunately, there appears to have been a vendor problem with these parts and they are prone to develop erratic contacts. This adds noise to the normal pulses, confusing the processor with the random extraneous "data". The faulty encoders need to be replaced. When the unit is working properly, check all the rotary controls on the front panel-- if one is going bad, often the others aren't far behind. I generally change them all while I have the unit apart if any are showing signs of erratic operation. They aren't terribly expensive, but they are mounted on a double-sided PC board, so they are sometimes tricky to get unsoldered.
Click to expand...

I've seen these faulty switches on a lot of different Macs. It is very common. Specially on the MX-132, 134, 119, 120, 135 & 136 - at least those are the ones I've tested in the past. I've talked to a Mac repair center and they tell me it's a dirty switch issue. The switches are sealed, but dirt still gets in there. They can be opened and cleaned, but a pain and not worth it since it's an inexpensive part and much better replaced with a new one.

When I got my MX-119 (used), I noticed this on the selector switch. Since I had opened up the unit, I just replaced all the switches. The parts are readily available directly from McIntosh or any of their authorized repair centers.

I believe most of the owners of these units don't even know about the problem since they mainly use the remote. You have to turn the switches manually to experience it.
 
I also have a MX-134 and the volume switch also exhibits erratic jumps when I turn the knob. Seems like the same problem. Do you know the part number?
I do have another problem which is the component video switching that was working just one week before. Either the Component video 1 or 2 input could not pass video properly to the Component output as I get unstable and bad video. The strange thing is both the Composite and S-video upconversion going out to the same Component video out works perfectly. So anyone has knowledge how to fix this would be really appreciated. Thanks in advance.
 
You must log in or register to reply here.
Back
Top Bottom