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Not so active blog

on December 31, 2008

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well..

not much to say.
many things happened as always.

but better be kept inside my heart.
for a memory of a live time.

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Dead Yaesu FT-450

Symptom : Yaesu FT-450 can not be powered on with no response from any button. Diagnotics : Since the on/off power is controlled by the main CPU, then the CPU is the first thing to be checked. The supply to the CPU should available and in the right value. There are 4 voltage regulators in the Control Unit board. They are for 8V, 5V and 3.3V supplies, plus one 5V standby that continuously supplying voltage to the CPU. Check all the voltage output from those regulators gave good results. So, it is not the regulator that fails. The CPU needs to be reset when DC power is connected to the radio. The reset is provided by PD GEN circuit. The way it works is when the power applied, /RESET line will stays low (0V) and after some delay, it will go high (5V). The IC Q4002 sense the input voltage in pin 2 to determine if the input voltage from power supply is good enough for operation. Problem Cause : A surge voltage from power supply, might damage the IC. But...

DC Dummy Load

One thing necessary during SMPS Testing is DC Load testing. This DC Dummy load is a device that act as load to the power supply. Its load can be adjusted from 0 to 12A. Here is the schematics : DCload.sch And here is the layout : DCload.brd Select MOSFET transistor that has SOA (Safe Operating Area) sufficient enough so that it wont be destroyed due to heat. The MOSFETs are running in their linear region, so heat will be produced significantly. A good heat sink and fan is necessary. I destroyed these three IRFZ44N .. The IRL3705 is better, but any MOSFET with higher SOA would work. The final assembly ...

Stripline Directional Coupler

This is still under construction and progress. So far, the result was not as expected. Perhaps need to do more experiment .. After placement in an aluminium box. Update : The previous result is not as expected, so I made an update PCB. Top ground plane was removed. I think this one has better response over HF and VHF. At 2m band, the response is quite flat at -30 dBm. On HF, the attenuation varies (as expected) and should be printed and referenced when using it on HF. So, I am happy with it. Ready to be used to monitor spectrum output from my RF experiments.

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