[Amps] Alpha 77 start up

[Jan Ditzian]

Paul,

I note that the light on the CW/Low button came on when I pressed that 
button.  Also, one of the meters is lit.   If I am reading things right, 
all bulbs are 28 VDC, so I expect that the 24 volt supply is OK.

I looked over the original Operating and Technical Manual, and there is 
a handwritten note on Fig 21, the CB2 board, that this unit has the 
CB-2A board.  There are other cryptic notes, but there is no specific 
change to the schematic.  I have no idea where to find a CB-2A schematic.

I will see if I can contact my friend with the test bench and a 24-volt 
supply.

Thank you,

Jan, KX2A

On 02/19/2011 02:29 PM, Paul Christensen wrote:
> Jan,
>
> 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 
> activating.
>
> 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" <ditzian at windstream.net>
> To: <Amps at contesting.com>
> 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
>>
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>
>