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Help on Mac 1900

firealley

firealley

Member
Hi folks,
My Mac was working fine. Now I'm to getting any output from the left channel. I've tried it on phono, tape, and FM. still nothing. Tried switching to mono and same problem. Switched speakers and still problem with left channel.
Any help or ideas would be helpful.
Thanks,
Joe
 
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The two most common issues causing a channel to go out on a 40+ year old receiver is either a dirty contact or switch in the preamp, control, section or a failed transistor in the output, amp section.

If you remove the horseshoe jumpers between the pre out and amp in and replace with a patch cord with the connection at the amp switched.....R to L, L to R AND if then the issue switches sides you know it has to be in the preamp section. If it stays the same it would be the amp section.

A MAC1900 is long past it's due date for a complete restoration but obviously a repair needs to be done first.

A experienced tech could examine the safety fuses inside and come to a quick judgement about the outputs but under no circumstance should you try to replace them without the proper test procedures in place.......you could easily destroy your speakers if the crowbar circuit allows DC to get to them. There is no relay.
 
Thanks,
I'll give that a try. Either way, it looks like I'll need to take it to service. Unfortunately, I bought this unit last year. I cleaned all the pots then sent it out to get the FM aligned. It was working great but I took it offline to clean the volume control again.( it was scratchy).. That's when this happened.. Does anyone out there know a good shop in the Orange County Ca. area?? Otherwise, I'm inclined to send this to Terry Dewick in Knoxville.
 
Volume control is a well known Achilles Heel on the 1900. You say the problem started after cleaning the control. Carefully work it back and forth checking it after cleaning it again. Got nothing to loose here.

Think eventually they get worse and worse and McIntosh does not have a direct replacement for it anymore.

Love mine though anyway.
 
c-dk,----You're right. I switched the jumpers like you said and the sound switched to the other speaker. Also, as Fairlane said, I will need to go back and re-check the volume control. I can't find any access to the pot to spray deoxit.. I don't have an electronics background so I'm thinking its going to have to visit the shop.
Thanks fellas! Any more advice?
 
Back in the day, any particular tech, had two or three spray bottles of cleaners they used for tuners, switches, pots, etc. I would think most were purchased because the price was right at the local arts supply house.

Unfortunately, some of these cleaners had solvents that attacked the adhesives that held the carbon trace material to the phenolic substrate in the controls. Years later the carbon began to flake off in mas.

I can remember the first time DOB introduced us to the three times more expensive blue and red can products from Cramylon. Only one local supply house stocked these products, they were much more expensive but a recommended product for Mac service so we started to use them.

These products morphed into the D5 and Faderlube we recommend today.

Mac parts does have a generic control that can be modified to work in all these 60s designed preamp sections.

Of coarse a bench test will need to be done to insure it is the volume control or is a problem elsewhere.
 
c-dk, thanks, looks like I received some good overall advice.. I'm leaning towards a full upgrade to the 1900. I would like to have the 1900 be hassle free for a while..
thanks,
JG
 
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