[time-nuts] LPRO101 Lamp Exciter Frequency

[Roberto Barrios]

Hi all,

 

I've got an LPRO101 that refuses to lock and you sure will be of great help. These devices are quite cheap but I'm trying to learn in the repair process.

 

I've followed PE1FBO's repair guide and everything noted there seems ok. I could not find a single suspect component. These are some notes I've taken on the unit after a 20 minutes warmup:

 

- Power input current during warmup is 1.2A and 0.4A after it.

- 10Mhz out swings between 10.000191 and 9.999875, taking 40s to go up and 60s to go down in freq.

- Lamp voltage is a steady 6.7V.

- The lamp glows a few seconds after powering the unit.

 

Placing a pickup look over the PCB, the analyzer shows peaks all over the place up to 2.5Ghz (it's limit), so the thing is alive.

 

There is one unexpected thing I found... The frequency of the RF power going into the lamp is 157.3Mhz, very stable. From the repair guide, it should be 70Mhz. I checked it with everything on hand (scope, counter, spec. analyzer) and there is no doubt about it. A clean sine of about 16V peak to peak, at 157.3Mhz can be found at the output (source) of the BF160 MOSFET.

 

Could this unexpectedly high exciter frequency cause the inability to lock or should I look somewhere else?

 

The deviation from the expected 70Mhz seems too big to me, but should I tweak the oscillator tuning capacitor (C901) to try to lower the frequency?

 

Thank you all,

Roberto EB4EQA

 
 		 	   		  
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