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+  MCI Console and Tape Machine Forum
|-+  MCI Consoles
| |-+  JH-500 Series Consoles (Moderator: Roginator)
| | |-+  "Jump start" preamps
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Author Topic: "Jump start" preamps  (Read 1213 times)
windmill
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« on: May 07, 2016, 11:07:24 AM »

Hi,

Console is a 528b.

I've just started using the preamps.  I have not recapped the preamps yet.

I have a handful of  preamps that don't work until I send a hot enough signal or crank the preamp
gain.  These channels will work for a while but when sitting idle need a "jump start" again to work.

Is this a capacitor issue in the pres?

Thank you:)
« Last Edit: May 08, 2016, 03:36:37 AM by windmill » Logged
Rob
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« Reply #1 on: May 08, 2016, 08:18:04 PM »

Try reflowing the solder on the Molex pins
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windmill
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« Reply #2 on: May 08, 2016, 09:04:45 PM »

Great thanks...I'll  reflow the solder on molex...was also thinking it could be bad/dirty pad switches?
I'll be able to reflow and check switches in a few days and report back.

Thanks!
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Rob
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« Reply #3 on: May 09, 2016, 06:08:20 AM »

Switches are also a definite possibilty.   The molex pins are notorious on MCI's.
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Harrison
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« Reply #4 on: May 13, 2016, 12:38:30 PM »

Rob Flinn and I have experiwnce of another 500 with daughter mic pres.
Yes, reflow the large and small molex solders on the mic pre pcb. Pull the mic pre on and off of the module to "clean" the $h**ty tin pins of the molex connectors.
We are looking at replacing the small molex right angle connector feeding the pad switch with gold plated ones to fix the console we look after.
The pad switch can be bad as well.
PC
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windmill
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« Reply #5 on: May 13, 2016, 07:33:43 PM »

Hi...thanks for the reply:)

I have reflowed the molex under the console (I also did this 5 years ago when I bought the console).
I've also tried to clean the pad switches.  Still getting mic pres that cut out but come back if cranking the gain while signal is input.

My I/O modules don't have any mic pres with daughter boards...components are straight to the module.

Maybe bad pots?  When the pres are working there is no scratchiness or distortion when turning the pot.

Anything else I should be looking at?

Thanks for all the help!

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Harrison
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« Reply #6 on: May 15, 2016, 01:39:32 PM »

Sorry, My error B vs C.
Don't bother cleaning Schadow switches, just replace them. The internal plating has worn; it's not just dirt.
PLease check also the solder pads of the output capacitor.

The other point is the preamp out / return on the patch bay.
On one that is iffy, can you take a patch cord and jump to a "good" channel to listen to the mic pre itself.
It might be the patch bay norrnalling contacts you are having to pop, not the mic pre itself.
PC
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windmill
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« Reply #7 on: May 15, 2016, 08:35:48 PM »

Thanks for the reply:)


I believe I have found the problem.  Ping Pong switches.

I have never used the Ping Pong function so it seems the inactivity of the switch is causing the intermittent behavior. 

I'll report back as I work these over the next few days.

Thanks again!




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Harrison
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« Reply #8 on: May 16, 2016, 10:59:51 AM »

If it's a 500B and you have not had to change the switches.....................
The 542B at Redbus had most og the key switches done at some point and the one at Eastcote, the owner bought box loads of Toneluck switches. Ongoing.
I'd forgot the ping switch, Yes.

You get to the stage where it's just a blanket change of say EQ Chan/mon, or the EQ in/out switches, and it's not worth fpaffing about with the odd one, settle down for the day and do a whole change of one type.
If you've got more than 2, 3, 4 ping switches...change out the lot.
PC
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