[MRCA] Got a AM3349 with no HV. LV supply/fans OK

[J Mcvey]

 I finally got onto this GRC106 amp. 
I learned that there is nothing easy about doing diagnostics on the AM3349. It needs a bunch of adapter cables just to bench test it. 

After much preparation, The problem turned out to be a  defective band switch motor (open), leaving the encoder in an "indeterminate" state which locks out the HV. It may be that a jammed mechanism may have killed the motor?

Ok, that's all well and good, but it looks like another nightmare to disassemble the tuning assembly.Are these motors available? I suppose they have to have the correct gear already pressed on the shaft, too?Yikes!
Also, The tube bias is called out to be -34 volts on the grids. This one had -25 volts each . Is that typical or has someone "screw drivered" this ?
Jim

    On Friday, May 27, 2022 at 08:29:41 AM EDT, Ray Fantini <rafantini at salisbury.edu> wrote:  
 
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HV is not applied until several conditions are satisfied. The big one is the band centering motors that includes the drum being set to the right channel and the ATU that’s actually the output tuning setting the two switches that select what band the radio is in and if its running a 50 Ohm output or whip.
 
It’s a common problem where the motors freeze and wont move so the ATU never gives its go ahead and HV is not applied.  Also remember that if the filament timer is not set the HV cannot be applied. You can check that by looking at the primary voltage on the service meter. If you had something like an air flow failure you never get the primary voltage indication.
 
The HV supply is somewhat bullet proof but I have seen the relays fail.
 
  
 
Ray F/KA3EKH
 
  
 

 
  
 
From: mrca-bounces at mailman.qth.net <mrca-bounces at mailman.qth.net>On Behalf Of J Mcvey via MRCA
Sent: Thursday, May 26, 2022 6:34 PM
To: mrca at mailman.qth.net; army-radios at groups.io
Subject: [MRCA] Got a AM3349 with no HV. LV supply/fans OK
 
  
 
CAUTION: This email originated from outside of Salisbury University. Please exercise caution when clicking links or opening attachments from external sources.
 
  
 
Any known issues with the HV supply ...or do I have to actually troubleshoot the thing?
 
  
 
Jim
   
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