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News: Please post general conversations, videos, music, and similar stuff in the "Tips, Tricks and General MCI conversations" section, use the Misc section for any product not listed in the categories, parts or custom projects. Thanks!

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 on: August 30, 2018, 03:18:20 PM 
Started by Berwyn636 - Last post by Rob
There is a story of a 500 series that had its frame bent while moving it round a corner before installing.   This meant that the middle channels did not engage with the motherboard connections.    I believe the remedy was jacking it up in the middle with a  bottle jack to gently bend the frame up so connecton was made for these channels ...........

 on: August 26, 2018, 05:42:43 PM 
Started by Berwyn636 - Last post by brianroth
With the desk I remember with intermittent channels (they were all in low numbered positions), I removed a bunch of the higher numbered modules so I could get a strong light and my head down into the frame to observe what was going on. 

The visual inspection revealed that the mother board connectors were not mating well with the channel strips.  It took some shimming to move the motherboard into a good position for reliable mating with the modules.


 on: August 26, 2018, 01:43:50 PM 
Started by Berwyn636 - Last post by Berwyn636
they appear random then sometimes they are next to one another

 on: August 24, 2018, 12:43:11 PM 
Started by Berwyn636 - Last post by brianroth
Are the intermittent channels randomly located across the desk, or are they in the vicinity of each other?


 on: August 24, 2018, 03:07:31 AM 
Started by Berwyn636 - Last post by Berwyn636
just when you push down on some channels they go in and out so I go through and wiggle an push on the strips til they seem like they're staying live then bolt em down but i still get intermittent dropouts depending on vibrations and what not.

 on: August 21, 2018, 07:09:11 PM 
Started by Berwyn636 - Last post by brianroth
What sort of issues?  I do recall one 636 desk which apparently had suffered some sort of "frame warp" and channel modules 1-9 (IIRC) had intermittent connection problems.  There was nothing obviously visible in the metal framing.


 on: August 21, 2018, 02:37:44 PM 
Started by Berwyn636 - Last post by Berwyn636
Anyone ever have issues with the 40pin motherboard connectors?

 on: August 13, 2018, 09:43:48 PM 
Started by adamb - Last post by adamb
I ended up "fixing" this...It was a pin that did not get seated from the motherboard to the interface lamp driver board.   Embarrassing.

 on: August 13, 2018, 09:41:18 PM 
Started by adamb - Last post by adamb
Hi MCI'ers,

My JH24 is not going into record, no record button light, no relay click.   Upon failure, the record light would come on sometimes (with no engage into record), but now does not even illuminate.  I'm starting my troubleshooting in the audio power supply and noticed that I'm seeing -18v on both test points 4 and 7 on the fan side of PS.   No noticeable part failure on the 18v regulator board.   The unregulated voltage input to the 18v card is +21.6v and -58.2v from J1-3 and J1-4, respectively.   The voltages from the solitron diode bridge inside the PS are +36.4v and -44.3v.

Where are the best points on the 18v regulator card to test for voltages?   

Once I'm done there, I'll need to do the same to the 24v board.   What are the best test points and voltages that I should see on that card?

Thanks for the help!

 on: July 06, 2018, 12:46:05 PM 
Started by Berwyn636 - Last post by TonesOnTail
I made some prototype boards based on some fine and much appreciated correspondence with Harrison off forum. It was something like a twin-T Barry Porter hybrid with 3 bands of fully parametric EQ utilizing the feed forward summing amps and onboard gain pots from the stock 4030 revision channel strip. It worked well and sounded smooth, except at the extremes of the boost/cut ranges where they started to hoot and feedback pretty badly. I had worked on some design changes to tame the oscillations of the filter amps, but had not gotten to running a second prototype run of PCBs.

Harrison had suggested bypassing the entire EQ section if the main modules, and replacing the EQ summing amps and pots with a more common feedback topology. This would more than likely be the way to go, but would add further to the cost and modification per channel. Things like CT pots, multi deck pots with switches, etc, are mucho $$.  This quickly goes into the territory of exceeding the market value of 600 series channel strips. Even the first prototypes I made were around $100 usd per channel, using PET caps, sealed pots, etc.

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