HW-100 S-meter problems

[Chris Iwata]

I had a HW101 which is similar to your HW100.  
 
The usual cause for the problem you have is a tube that is gassy, but if  the 
voltages are steady than not in your case.  Bear in mind that small  
variations in these voltages add up to big changes in the  S-meter. 
 
Any of the resistances in the S-meter circuit are suspect. Resistances may  
be intermittant or drift. Maybe your freeze mist didn't peg the problem.
 
Spray some contact cleaner through the zero pot. This pot is the  most likely 
cause. Or, try disconnecting it and using another pot  temporarily to 
diagnose.
 
Other suspects are the resistors connected to the SG.  In  the HW101 these 
are 1 watt resistors, R107 and R106.  The 100K resistor is  the most likely 
culprit. Replacing these resistors with carbon or metal  film resistors instead of 
the carbon composition resistors they were is a good  idea anyway, as these 
vary less with temperature. 
 
Another unlikely possibility is the shunt resistor: In the HW101  this is 
R115, 150 ohm
 
Chris, KL7DM
 
In a message dated 12/11/2007 5:00:41 P.M. Pacific Standard Time,  
k7mks at COMCAST.NET writes:
 
S-meter  intermittently reads correctly and then at times it sits on zero.  
At  times it will not peg to the right when the RFG is full CCW.

V3 and V4  have been changed. S-meter zero pot checks OK.  P, SG, K, and G 
voltages  of V3 and V4 check OK per manual and do not change from the normal 
S-meter to  non-working S-meter situation.  Both relays have been  cleaned.

When working correctly it reads over S-9 w/ calibrator signal  and then fades 
slowley to the non-indicating position of  S-0.

Freeze-mist, heat, resoldering connections, tightening board  screws so far 
have failed to discover the culprit.  

Just turned  the -100 on and the meter goes full right w/ RFG full CCW.  
Calib. signal  reads 9+ but wavers up and down a S-unit or so.  Eventually it will 
fade  down to S-0.

I'm hoping there is someone who has experienced a similar  problem - I feel 
like I am going around in circles.

Thanks

Joe  k7mks





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