# Flickering mute illumination LED on 4 yr old McIntosh Preamp

Status
Not open for further replies.

#### richh

##### New Member
Hello, I have a very annoying occasionally flickering Mute button illumination. It will do a while and then stop for a while. I called McIntosh and they are not very helpful other than sending it to them which will cost at least $100 to mail to them and then a bunch for them to repair. I just got back another component back from repair and it cost like$400 to repair and all that happen was the internal battery went dead and the memory got erased so they had to reinstall the operating system. My question is 2 part. Can the LED be replaced on the board and what are the chances that it is just a bad LED?

#### richh

##### New Member
Here is a pic of the board/LED

#### Attachments

• IMG_20201203_211236.jpg
1.1 MB · Views: 50

#### Diver300

##### Well-Known Member
Is the LED flickering when it's supposed to be on all the time?

If so, it's possible that it's just a bad LED

#### KeepItSimpleStupid

##### Well-Known Member
The top LED pin looks bad. There "LOOKS" like a separation between the lead and the solder. Freeze spray is used as a diagnostic tool. See https://www.chemtronics.com/ultimate-guide-to-diagnostic-freeze-spray

In two basic ways:
1) The spay can cause an intermittant to become solid. Like you said, it warms up and mute doesn't work. If freezing the joint causes the light to work, then there is a good chance you found it.
2) watching the spray evaporate exposes cracks. They take longer to dissipate.

The freeze spray usually comes with a targeting straw like some spray cans of WD-40 have.

You could do those tests. I'd still like to see the SM.

I think of a SM as an insurance policy, so get that. The LEDS could be an insurance policy too.

I worked on two Macintosh valve amps. A friend lent them to someone and they wanted them louder, so the fed the output of one to the input to another. I also worked on an amp that was borrowed from a relative of the owner and was placed in service at a disco. No shop. 5 were asked. I could see why. Components puddled on the PCB. I took it.

I live East Coat US and I have more than a full plate, but re-soldering the joint seems easy enough. I sent something to someone and never got it back and I wasn't happy. There is always the chance I could die in the time frame. You at least have an out. You can purchase what got lost. Postage and a small token amount for my effort via PayPal. I don't have any freeze spray right now.

I had a piece of unobtainium. I sent him something (large real blue print) I wasn't interested in and made a copy first. I had some large blueprints which I might be the only one in the world that has them all. I was trying to figure out how to digitize the drawings.
I used a CAD outfit and they put the drawings on their scanner when it was available for $10.00 a drawing and$5.00 to print it. They had the drawings for >2 weeks. They scanned them in TIFF and PDF.

They tried a program that could help convert drawings to CAD formats, but it didn't work. The entire set cost be about \$150.00 and they did some of them. At the time, I did not realize I had pieces of two different designs. It's still not sorted out.

I helped a now friend in .au create a product with the unobtainium info I had. I did get the free product and the schematics in the end. We have an NDA that I don't share without permission and likewise with my drawings which are now scanned. Some were very large blueprints. In the end, we learned that two varients of the product exist. I have an early model. Externally they are the same. It's possible the serial numbers provide a transition.

Mine uses a high quality PCB and looks expensive. Mine has a different IR receiver board, Electrically, they appear to be the same..
We know there are 120 versions and 120/240 switchable versions and even 100V versions.

I also helped him find a design fault in another product he made for home. The chip he used, one set of inputs were CMOS and the other TTL for similar functions on the chip he selected.

I signed an NDA for a commercial product which helped me: It told me that the power brick was unregulated and polarity didn;t matter.
I had to use a regulated power brick for what I wanted to do. I wanted a way to detect the phone off the hook and not talking for 15 min and light a LED and to blink a LED when ringing. I settled for immediate off hook and ringing.

Last edited:
Status
Not open for further replies.

Replies
47
Views
3K
Replies
28
Views
9K
Replies
4
Views
1K
Replies
2
Views
3K
Replies
3
Views
2K