[Amps] Titan 425 keying issues

[Jim Brown]

I own three of these amps, and had to troubleshoot them several times. 
To make that easier, I drew up the schematic in AutoCad and printed it 
to several pdf files that are on my website.  k9yc.com/publish.htm

Except for the tubes, all of the circuitry is garden variety discrete 
transistors, diodes, and resistors that can be replaced by readily 
available parts. The only troubleshooting tool I needed was a Simpson 
260 to check the semiconductors. You'll need to remove the boards to 
troubleshoot them. Check EVERY semiconductor -- when one blows, the 
fault often takes out others, including a power resistor that's part of 
the bias circuit.

As to "won't key up" -- make sure that you're keying it properly. The 
keying logic in this amp positively prevents "hot keying" by monitoring 
the position of the vacuum relay. The transceiver MUST have enough 
keying delay time set that (after PTT from the transceiver) the relay 
pulls in before the transceiver sends RF. My experience has been that 8 
msec is enough, and this is the default for many (most?) rigs. I've 
never tried less.

73, Jim K9YC

On 7/12/2018 9:45 AM, martin dulaney wrote:
> Hello everyone I am hoping that some one on here can help me out!
>
> recently purchased a used titan 425 ran great the first week ! although the meter lights were out .
>
> 28ma 1300-1500 out opened it up the bulbs were 12 volt in series replaced them closed the cover back up
>
> powered it back up meters light up it wont key up??
>
> tried removing the bulbs no joy replaced Q1 and Q2 on the bias board  still no joy
>
> checked all of the relays K5/K4/K3/K6 they all close when powered directly bias on terminal 85 on the bias board reads 8.5 volts all of the time.
>
> relays K5 changes state when you switch from standby to operate
>
> 28 volt source on pin 7 from ps reads good
>
> meter reads approx 2.4 kv when in ep??
>
> at a loss here hopefully some of you gentlemen have some clue as I sure don't
>
> would also be interested in purchasing a used but good bias control board
>
> Thanks And 73's Martin KN4DXD
>
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