MAC 1700 Left Channel Very Weak

U

Ulysse

Active Member
Got a nice-looking MAC 1700 over the weekend. However, now left channel is very weak and barely audible, but right channel sounds good. I've tried all connections, FM radio, tape, phono and aux.

I remember the left channel was working for a very short period of time yesterday when I connected the phono, but no longer.
Another interesting thing is when I connect the headphones, the left channel works but the right does not, as if the left and right are the opposite of the speakers.

I opened the bottom cover, and sprayed some contact cleaner to the volume and balance. Nothing changed.
I also measured the DC offset, the both speaker outputs are surprisingly low at close to zero. None shorted.

Any idea what might have gone wrong? Thanks a lot!
 
Most commonly the Tape Monitor switch on the front panel, flush it well with DeOxit D5.
 
Also, there is a thick layer of stuff from oxidation on the RCA connectors. What's the best way to remove that? Steel wool? Thanks.
 
The input selector is overridden by the tape monitor. Apparently it's cutting out one channel even when it's in the off position.

Steel wool should work well however the inside pin connectors should probably be cleaned as well. I would think toothpicks and contact cleaner would be helpful for that task. Also bear in mind McIntosh RCA jacks are notorious for becoming corroded where they make contact on the inside of the chassis over time. Cannot say whether this malady is common in the MAC1700.
 
Thank you both for the tips. I'll try these tonight.

How do I open the grills on the top to get access to the pre-amp boards and the power caps? Looks really dirty down there. The tube section grill can be easily lifted off.
 
You guys are good! It is the tape monitor switch. Don't have DeOxit at hand, so I sprayed a lot CRC twice, and it worked!
However, there is still some issue with both phono. The channels are not stable, the sound sometimes jumped around between the two channels. Maybe it hasn't been used for two long. I'll break it in for a few days and see what happens...

I managed to open the cages. Both need to be opened from the bottom with the bottom lid off. There are two hex head screws holding the pre-amp cage. For the power stage cage, there are hex head nuts.
 
I'm no fan of using steel wool on electronix or mechanisms, ever!
Limitless unintended consequences abound, use bits of paper towels and WD-40 to clean jax and plugs.
 
Have been listening to vinyl for a few hours. Still having issue with both phono inputs. The channels are not stable, the sound sometimes jumped around between the two channels, or sometimes completely gone for a second or two. Tested the turntable on another amp, and it works fine.

Any idea what might be the problem? Thanks.
 
Still having issue with the phono periodically losing sound, all other inputs are very good. I read it somewhere that the power input 10v filter caps should be replaced. I decided to replace all those paper caps, as I heard they are problematic after so many years.

I found the following:
Power Ouput PC Board:
100uf 15v x 2
180uf/200uf 3v x 2

Pre-amp
10uf 3v x 4
100uf 15 x 2
1.5uf 35v x 2

On chasis power supply
100uf 15v

Any recommendation on what capacitors to use to replace these?

Thanks!
 
I am not a fancy cap kind of guy. If the cap needs to be axial, I go with Illinois axial electrolytics. If I can fit a radial cap in there (stand it up on end to replace an axial) then I use Nichicon audio grade caps--UKZ, UFG, UKW, or ES if you can use a nonpolar. I've also used Elna and panasonic. My favorite pieces of audio gear that I've restored have Nichicons in them. (I used Elna in my HK330c, and the result was good, warm sound, but I perceive it as a bit rolled off on top, and the caps took 100+ hours to sound the way they do now, and my NAD 3020 with Nichicon audio caps blows it out of the water).
 
mnmmt said:
I am not a fancy cap kind of guy. If the cap needs to be axial, I go with Illinois axial electrolytics. If I can fit a radial cap in there (stand it up on end to replace an axial) then I use Nichicon audio grade caps--UKZ, UFG, UKW, or ES if you can use a nonpolar. I've also used Elna and panasonic. My favorite pieces of audio gear that I've restored have Nichicons in them. (I used Elna in my HK330c, and the result was good, warm sound, but I perceive it as a bit rolled off on top, and the caps took 100+ hours to sound the way they do now, and my NAD 3020 with Nichicon audio caps blows it out of the water).
Click to expand...

Thanks a lot for the advice.
I found a list from a thread here. Looks like he mostly used Panasonic FC series, and the radial caps can fit.
Can't find all the caps needed on Mouser or Digikey using NIchicon series you mentioned, so I might just go with the Panasonic, unless there is a big difference in sound quality.
 
Pulled the cap in power supply for phono. It tested 150uf vs the specs 100uf, and I think this is the issue. I installed an used cap as a temporary solution, and it seems have solved the previous issue of losing sound periodically, at least for the last hour or so I've been listening to it.

Still having louder than usual background noise on one side of the speaker. No such issue using CD. May still need to recap the preamp and power output.
 
We went around this merry go round last week with a MA5100 and it's similar if not Identical phono EQ circuit.

You need to short out the phono input to look for noise and/or using a reverse RIAA test circuit inject a known good signal from a signal generator and then with a scope look for your dropped signal or added distortion.
 
c_dk said:
We went around this merry go round last week with a MA5100 and it's similar if not Identical phono EQ circuit.

You need to short out the phono input to look for noise and/or using a reverse RIAA test circuit inject a known good signal from a signal generator and then with a scope look for your dropped signal or added distortion.
Click to expand...

I don't have the equipment or knowledge to do the testing you mentioned. What did you find out on MA5100?
 
You will have to read the MA5100 post from a week or so ago. I did restart his post because he was looking for parts subs when the server update dumped his original post.

I believe he determined that his MC cartridge did not play well with the 50 year old phono design, but his Grado cartridge did.
 
Just want to report back on my progress. I recapped it using Nichicon audio grade caps, except the big filter caps. Now everything has been working perfectly. Has plenty of power to drive my Celestion 662.

There is a very low buzzing sound if I get really close, but not audible sitting 10 feet away.

The only complaint - too much bass Had to turn the bass knob to 1/4 level...
 
You must log in or register to reply here.

Similar threads

N
Mac 1700 Dead channel help!
Replies
5
Views
1K
skippy_ps
skippy_ps
L
Mac 4100 problem.
Replies
3
Views
922
longgone
L
sgarwood
McIntosh MAC 4100 weak left channel
Replies
12
Views
2K
c_dk
C
M
Mac 1700: Help
Replies
2
Views
648
monkeydog
M
cspyon
Right channel weak on MX110z
Replies
5
Views
199
cspyon
cspyon
Back
Top Bottom