[Top] [All Lists]

Re: [Amps] Alpha 77 start up

To: "Jan Ditzian" <>, <>
Subject: Re: [Amps] Alpha 77 start up
From: "Paul Christensen" <>
Date: Sat, 19 Feb 2011 14:29:21 -0500
List-post: <">>

The problem appears to be isolated to the three-minute warm-up timer. 
You're seeing 2600V which is correct while the three-minute  timer is 

First, measure the +24 VDC supply voltage.  It should be fine since you 
don't seem to be blowing the step-start fuse.  That would render the amp 
completely dead after the step-start resistors finally blew and threw 
shrapnel all over the inside of the amp.

The timer circuit is on circuit board CB-2 and is very simple in operation. 
Upon sensing +24VDC, C207 (22 uF) begins charging through R222 (10 meg). 
This in turn activates SCR Q207, which simultaneously switches a more robust 
SCR Q208.  Q208 fire and pulls in relay K202.  Once K202's contacts close, 
+24VDC is supplied to the "READY" lamp (and other amp circuits) and the amp 
is ready to make power.

CB-2 unplugs from an edge-card connector so you can safely do some 
troubleshooting outside of the amp -- If you have an adjustable +24VDC bench 
supply, use it for testing.  Otherwise, be extremely careful when testing 
components in the amp.  CB-2 is not far from the HV contact points.

As W8JI once said, he's never had to troubleshoot an amp with AC power 
applied.  He's right.  It may take longer, but it's a much safer way to 
diagnose a root problem.  If you've ever diagnosed an amp problem by 
yourself, now is not the time top learn on your own.  Get on-site help if 
you cannot work on CB-2 outside the amp.

Paul, W9AC.


----- Original Message ----- 
From: "Jan Ditzian" <>
To: <>
Sent: Friday, February 18, 2011 10:59 AM
Subject: [Amps] Alpha 77 start up

>I just received an Alpha 77 Dx, modified as a two-holer, as a gift (I
> have very understanding friends).  However, it came with a problem--it
> does not work. The startup light does not come on.  The previous owner
> sent a board back to Alpha to fix this problem, and their paperwork
> shows that they repaired it and then tested it in an Alpha 77Sx, which
> is equivalent to the two-hole modified Dx, and it worked.  However,
> after putting the board into this rig, the problem remains.  Since I am
> new to this amp, and did not have it integrated into my station, I did
> the following checks:
> I set up the amp with no exciter, but with power, and the fan comes on
> and the voltage goes to about 2600 volts. I followed the regular startup
> procedure and, sure enough, the light does not come on after six minutes
> (it is supposed to take about 3minutes).  I then put a cable into the
> relay jack on the back, repeated the above process, went ahead and put
> the amp into CW/low power mode after a six-minute wait, and then shorted
> the relay cable.  I did not hear a relay click--nothing happened.
> Can someone help me to isolate the problem with this amp?  Until this
> happened, the previous owner (the donor of the amp) was using it without
> a problem.  There was no cataclysmic event that preceded the failure to
> start up.
> I can imagine problems like bad contacts on the board connector, or
> perhaps the failure of another relay somewhere.
> Thank you,
> Jan, KX2A
> _______________________________________________
> Amps mailing list

Amps mailing list

<Prev in Thread] Current Thread [Next in Thread>