Focusrite 428 schematic request

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pucho812

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Anyone have schematics for the ISA 428, 4 channel mic Pre? One arrived from a thrift store and it powers on but every led comes on and stays on and none of the switches work. I assume it’s psu related. I can measure +/-15vdc on the 5532’s which is within working voltage for the ic but not sure if that’s correct. Also  not sure what else the psu outputs other then phantom power. I know they are prone to failure from heat.  But wouldn’t be bad to have working.
 
You could contact focusrite. They usually do not hand out schematics. But if you describe your unit's problem to them, they might give you a pretty detailed walkthrough on what components to check. They might also have the necessary components, if unobtainable otherwise.
 
Apart from the bipolar op amp supply from memory is has 317 creating 12v.  Another 317 for the 48v through whch 30v is derived through a transistor.  There might be another couple of rails as well but I'm not quite sure.
 
Script said:
You could contact focusrite. They usually do not hand out schematics. But if you describe your unit's problem to them, they might give you a pretty detailed walkthrough on what components to check. They might also have the necessary components, if unobtainable otherwise.

I know they do not hand that out. I know there are mushroom caps in the PSu, from first glance so that will get fixed.

Rob Flinn said:
Apart from the bipolar op amp supply from memory is has 317 creating 12v.  Another 317 for the 48v through whch 30v is derived through a transistor.  There might be another couple of rails as well but I'm not quite sure.

yes. that is helpful. thanks.
 
Hey puncho it seems like you could derive the power supply from the ISA430 doc on the tech section.  Also I’m sure it’s caps.  I,ve repaired 3 focusrite pieces, and caps in the audio path usually are in need of replacing with high esr.  They do run hot inside.  Also the ribbon cables or harness can have problems.   
 
fazer said:
Hey puncho it seems like you could derive the power supply from the ISA430 doc on the tech section.  Also I’m sure it’s caps.  I,ve repaired 3 focusrite pieces, and caps in the audio path usually are in need of replacing with high esr.  They do run hot inside.  Also the ribbon cables or harness can have problems. 

thanks for that  8)
 
well I checked with focusrite, they wouldn't even give me a partial schematic or tell me any pertinent information regarding what I should see on the output of the PSU and where to test for it.  No worries, I got the ISA430 from the tech docs, I'll use that as my guide and go from there.
 
Try to isolate the diferent rails outputs in the PSU and measure them.

If you have bulged electrolytic caps in the PSU replace them all even the not bulged ones, Shotgun Method

if the original caps are 85degrees replace them for 105degrees caps.
Or ir they are 105 degrees already replace them with higher voltage caps if they fit the spots
 
Whoops said:
Try to isolate the diferent rails outputs in the PSU and measure them.

If you have bulged electrolytic caps in the PSU replace them all even the not bulged ones, Shotgun Method

if the original caps are 85degrees replace them for 105degrees caps.
Or ir they are 105 degrees already replace them with higher voltage caps if they fit the spots

of course  :) that's the first part. I just found it funny they wouldn't even give me test points and voltages readings.
 
Yeah, replace "funny" with "stupid".  I had one come in and besides bulging caps it had some damaged pots.  The "official" replacements were from a third party and amazingly expensive.  No respect for F*&+usrite anymore.
 
mjrippe said:
Yeah, replace "funny" with "stupid".  I had one come in and besides bulging caps it had some damaged pots.  The "official" replacements were from a third party and amazingly expensive.  No respect for F*&+usrite anymore.

Jesus that's nutty. I get wanting to protect intellectual property and qc of work but come on. My former bench stint for a company wouldn't hand out schematics, but we would provide test points and procedures and if you talked with us on the phone long enough, you could draw out a schematic from what we told you.  in fact I had a guy send me a hand drawn  schematic from the notes we did verbally and over e-mail, aside from polarity being flipped he was on point with the circuit in question.
 

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