[Elecraft] KPA100 problem

[n0jrn]

Don:

Just to clarify !

The -28V's I'm seeing at pin 8 of U4 is measured without the IC installed.

Lets say for the sake of conversation that I install a good MAX1406 and it 
draws on the rectifier circuit a minimal amount.

Would / could that bring the -28V's back into specs for this chip???.   ( I 
have to figure Wayne designed the circuit taking this draw into 
consideration )

OR      is my -28V's so abnormal that I need to be looking at other issues 
in my rectifier pack to bring this negative voltage back into spec ???

Could the negative voltage I'm getting be responsible for damaging this chip 
???

I have 2 new chips coming from Mouser.   I'm not installing them until I'm 
satisfied that I've checked and double checked   EVERYTHING   involved.

Thanks again and happy holidays to the group:

72             Jerry             N0JRN
----- Original Message ----- 
From: "Don Wilhelm" <don at w3fpr.com>
To: "n0jrn" <n0jrn at mchsi.com>
Sent: Monday, December 14, 2009 6:22 AM
Subject: Re: [Elecraft] KPA100 problem


> Jerry,
>
> I will take back what I said about U4 - it is faulty.
> That negative voltage is there only to allow the RS-232 drivers to produce 
> a negative level, the current draw should be minimal.
> The only thing U4 does is convert RS-232 levels to TTL levels and 
> vice-versa.
>
> Actually -28 volts is a bit much and does exceed the maximum speced 
> voltage for the chip.  -12 volts is more than sufficient and even -5