EEVblog Electronics Community Forum
Electronics => Repair => Topic started by: jkf1000 on February 10, 2017, 08:30:07 pm
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I am just in the process of checking my receiver prior to sale and I found a burnt resistor R6 top right on the keypad interface board. I have looked through the manual and googled for more info but have not been able to identify the correct value for a replacement. If there is any one out there with the same or similar receiver could just pop the lid and check for me it would be greatly appreciated. The receiver itself appears to be working 100% and the current measured value accross the resistor in circuit is around 73ohm. Thanks in advance.. Karl
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Looks to be either 56\$\Omega\$ or 560\$\Omega\$ in this picture:
http://radiopics.com/By%20Make/Lowe/Photos/Lowe_HF-125_Keypad%20Option.jpg (http://radiopics.com/By%20Make/Lowe/Photos/Lowe_HF-125_Keypad%20Option.jpg)
I favour 56\$\Omega\$ because I think the ring colour looks black and also it would be difficult to fry a 560\$\Omega\$ with the 12V supply of the radio. Does this radio use the same keypad as the HF150? - If it does you could possibly compare the schematics - I'm guessing that that resistor is used to supply power to the keypad and will be overstressed if the jack-socket is shorted.
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I made the same assumption about powering the keypad. It may be that it has been shorted by plugging in the keypad while the unit is powered. I am not sure if it is the same as the 150 model and I haven't done any reverse engineering but I will explore deeper before replacing it. Personally I still think it is a 560 \$\Omega\$ but not 100% certain. May try that first and check for full operation but with only a shortlist of two values it should be a fairly straightforward fix.. Karl
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Just checked the HF-150 and 225 manuals which supply a full schematic for the keyboard interface (same interface in both) but unfortunately they are different to the earlier 125 model. I am going to try a 560 ohm first and if that works ok leave it at that. On the later models the keypad is fed from a 150 ohm resistor but running off a 8v supply line. Nothing to lose by trying.. Karl
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You might find the schematics handy! ;D
http://www.dream-machine.myzen.co.uk/Lowe/HF-125%20(Schematics).pdf (http://www.dream-machine.myzen.co.uk/Lowe/HF-125%20(Schematics).pdf)
Good luck.
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Thanks for the link but unfortunately the interface board isn't included on any of the schematics I have found, only the main board. I have measured a few voltages and have fitted a 56ohm as a replacement and now everything is back working perfect. thanks to all for their input.. Karl