32670Re: [Heathkit:Yahoo] Heathkit HW-2036A synth board problem
- Jan 15, 2014Hi JesseHi-K ceramic capacitors are extremely temperature sensitive and so should only be used for decoupling - in case one has crept in to a tuned circuit by accident.Can you measure the supply voltage to the VCO to check that it is not changing with temperature?Are all of the resistors within their tolerance specs? Solid carbon types age high.Does the cover have any direct effect on frequency because of it proximity?Are there any leaky capacitors in the synth control loop?73
Bob F Burns G3OOU
C Eng, FIET, MSE
Secretary of Crystal Palace Radio & Electronics Club: www.g3oou.co.uk
Technical web site: www.qsl.net/g3oou
@BobFBurns on Twitter: http://twitter.com/BobFBurnsIn a message dated 15/01/2014 00:55:37 GMT Standard Time, landrejl@... writes:
Thanks for all the comments on me trying to choose a Heathkit HF rig. I have an SB-301 coming this week, half of my "twins" set. My other current project is my Heathkit HW-2036A 2 meter radio. Still working on my HW-2036A 2 meter radio. The problem I am having is that the synthesizer will not lock when the radio is warm. Found a service bulletin online that said to replace the tantalum capacitor on synth board, 417-801 transistors on VCO board and Q401 transistor on synth board. I have done all this and alignment of the VCO is much better now. However, the radio still won't lock after it gets barely warm, less than 30 minutes on standby. When I leave the cover off the radio and leave on standby, it works fine all day with no problems xmit and receive. Even had a conversation with another ham back and forth for an hour last night and it worked fine the whole time. Put the cover on and it won't last long.
I have tried a hair dryer on low setting over board and synth lock light goes on in less than 5 seconds. Something is real sensitive to heat. The 1 transistor I replaced is Heath #417-801. There are about 7 more of these on the synth board. Any other ideas before I replace all the transistors? Anyone else run into this problem? Thanks in advance for the help!
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