MX-117 restoration

txturbo

AK Subscriber
Subscriber
Just picked up my first McIntosh!

I have been looking for an MX117 for a while and one finally became available near me so I decided to take a look. It was cosmetically in very decent condition the glass faceplate was basically perfect and the wood case was 7.5 out of 10. I did a quick demo of the unit, seemed to tune in stations and the preamp was quiet except on phono, it had a bit of a buzz. This may have been the turntable that was connected, not really sure yet. The unit came with the original receipt, owners manual and schematic.

I got it home and powered it up with a freshly rebuilt Dynaco 400 as a test mule. It sounded ok for the basic test that I did.

I then noticed a problem, no FM stereo. Signal strength is fine. I pulled the IF wire from the front end and injected an IF signal. No joy..

So I started to look for a service manual but had no luck. Maybe someone has one? I see that the Berners site has it but I don't have any mac manual to trade.

In the mean time I started to look at the schematic. The 19KHz test point is basically dead. So I suspect that the TCA4500A is having a problem. I ordered an LM4500AN as a replacement.

I can also tell that the tuning cap is dirty, the signal strength is a bit noisy as stations are tuned.

I did a quick search and did not find much on the MX117 as far as restoration go. Has anyone done a recap or alignment? The lamps all seem to be working. I am not sure how LED's would look. The lamps at the end of the dial are quite dim, I suspect this is normal?

I really like how everything is so tidy and each board can be removed for service without much trouble. Not what I am used to at all!

I need to find a mac amp to go with it...

43875811841_ea3168e30f_b.jpg

43875812071_8483e0a90f_b.jpg
 
Congrats on a beautiful tuner/preamp. I own a MX114 and kinda similar I think. The dial lamps could look dim as there is switch that goes from bright to dim, check that. I continue to use the regular bulbs (luckily) and my tech installed a small soft start on my 114 to help preserve the bulbs and the on/off switch. I use a MC250 for the amp and it was rebuilt as well, they make a great combination IMHO... Good luck with that 117!
 
Always loved the MX117 - just a lotta bang for the buck. The MC2155 power amp is a great match and readily available.

Plenty of talent here to help you get it in tip top shape.
 
A friend of mine had a MX 117 and a MC 7200 driving two pairs of ML-1C with a MQ 107 EQ, talk about a winning combination. That 7200 would put out close to 544 watt peaks and 392 watts continuous across 4 ohms. As it didn't have autoformers, what it would do cross 2 ohms and 1,5 ohms was scary. It was designed to drive flat paneled electrostatic and planar speakers where the impedance dropped close to 1 ohm in the high frequencies with out generating a fuss. It was the first Mac amp with the .005% capability. Its signal to noise is 10 db short of later Mac amps and 20 db short of the balanced Quad mono amps. If you don't need big power the little 7100 does a great job. It just doesn't have meters. From that same period you might want to check out a 7150 with autoformers and meters.
 
Always admired that model. Standalone tuner comparable is the MR75. Good luck with it.
 
Got the 117 from Tom and is mint...and plays beautifully. The tuner plays as well as a cd and picks up many stations. Matched well with a 2205.
 
Today I received the service manual from Audio Classics. I am quite impressed by the service manual. The alignment instructions are very well written.

I have been able to make some progress, I now get the 19 kHz signal. The procedure calls for removing the stereo auto blend IC1004 from the socket and placing a jumper on the terminal strip to the right of the front end. The jumper goes between pins 1 and 3. Pin one is nearest the transformer.

With the jumper installed the frequency meeter shows 21kHz at the 19 kHz test point. A slight adjustment to the R1052 pot and the frequency now shows 19.00002 kHz.

And the MPX light illuminates :)

Before I get into the alignment I am going to clean the tuning cap and replace the electrolytic caps throughout the unit.

42233333320_a97c5272d9_b.jpg

43993905492_89a0ac7d3e_b.jpg


42233333210_439a90e3f0_b.jpg
 
I'm curious, how you solved the problem of not having 19 kHz on pin 11?

Welcome to AK..

Just follow the info in the post above. Look at the pictures for location.

1. Remove IC 1004.

2. Place a jumper on the terminal strip to the right of the front end. The jumper goes between pins 1 and 3. Pin one is nearest the transformer.

3. Ajust R1052 until you get 19 kHz at the test point.
 
I don't remember at this point but I don't think it was. It was simply an alignment problem. If i remember the test point can not be measured until you pull IC 1004 and jumper the front end. Once I did that I was able to read the test point.

A cheap and dirty test is to simply move R1052 a bit and see if the stereo light comes on. If it does then you know that it's just an alignment issue.

If you don't have the gear to do the alignment but the stereo light works if you ajust R1052, move the pot in one direction until the stereo light comes on then move it until it shuts off. Then set it to the middle of where it went on and off. This will give you a decent alignment of this part of the circuit in most circumstances. Some alignment procedures describe this technique and don't use a frequency counter.
 
Last edited:
Back
Top Bottom