QSK Issues/Fixes

 NE7X - 01/29/2012



*** DANGER ***

RF Amplifiers Have Lethal HIGH VOLTAGE Inside





When amplifier is keyed, the PPT line is activated, the vacuum relays chatter because they are not fully pulling in.


A bad filter cap on the +12 VDC line was found. Using a oscilloscope, AC ripple on the DC supply was over 12 VAC. Added a 2200uF cap across the +12VDC line to ground and everything is now working properly.




When the PPT line was activated, the vacuum relays would intermittent random drop out after 1-2 minutes, or the relays would pull in one time when keyed and not the next time keyed.


Using a DC volt meter, the +26V supply was pulled down to about +20 volts every time the HV Mercury Relay was energized. Relay has a 26V coil off the same supply. +20 was not enough voltage to keep the vacuum relays etherized.  Add a small +24VDC laptop power supply inside the amplifier, wire it to only drive the SEQ-QSK sequencer and vacuum relays.




A 1ms +5000V spike occurred when the ALC diode shorted inside the HV power supply circuit, blowing out the SEQ-QSK sequencer.


Installed a TVS (transient voltage suppressor) diode across the +12VDC input on the SEQ-QSK. The TVS will provide very fast responding when handling transient power spikes up to 1500 watt power. Considering the arc is a very fast and short duration phenomena, a TVS could possible prevent a failure of the SEQ-QSK.


 http://Mouser.com sells them for $0.59 each in single qty. They break down at around 18 volts which would be a good voltage to stop any over-voltage. The regulator on the SEQ-QSK is rated at 30 volts maximum input, so 18 would be a good level.


The Mouser part number is: 863-1.5KE18AG


Mount the TVS directly on the SEQ-QSK board by soldering the cathode lead into the +12 volt hole and the anode lead to the closest ground hole. It is important to keep the leads of the TVS as short as possible as the inductance of the lead length can cause an overshoot. And the overshoot is what you want to suppress, not make worse. Leave enough TVS lead from the +12 volt hole to allow you to attach the +12 volt line to it.




The QSK circuit was working perfect, however now when the transceiver is keyed, reflected SWR between the transceiver and RF amplifier is infinity. When keying the amplifier, the vacuum relays can be heard clicking, the yellow LED on SEQ-QSK is blinking (heartbeat) and all four green LEDs on SEQ-QSK are lit. HV check shows good, however there is no Ip idle current (~200ma) showed on Ip meter.


Check the BIAS circuit. Possible failed parts, 1) Fuse (if installed), 2) 10V BIAS zener, 3) Bad BIAS switching vacuum relay.





RF amplifier had a HV (High Voltage) surge, after which the vacuum relays now "chatter" when amplifier is keyed.


Voltage spike took out the 78L05 + 5VDC regulator IC on the SEQ-QSK. After replacement of regulator IC the issue is not resolved, the program PAL IC is bad. Contact JWM Engineering to obtain a new SEQ-QSK PAL IC at: http://jwmeng.com



Life is too short for QRP!!

Happy DXing



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