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Vintage Amateur and Military Radio Amateur/military receivers and transmitters, morse, and any other related vintage comms equipment. |
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10th Feb 2017, 10:41 pm | #1 |
Retired Dormant Member
Join Date: Apr 2016
Location: Rotherham, South Yorkshire, UK.
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Lowe HF-125 resistor identification
Helo to all, just posted this on the EEVblog but with hindsight I thought on here would be a better platform.
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 that could just pop the lid and check for me it would be greatly appreciated. The receiver itself appears to be working 100% and the measured value accross the resistor in circuit is around 73ohm. Thanks in advance.. Karl M0KRL |
11th Feb 2017, 12:45 am | #2 |
Nonode
Join Date: Oct 2010
Location: Tintinara, South Australia, Australia
Posts: 2,324
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Re: Lowe HF-125 resistor identification
http://radiopics.com/By%20Make/Lowe/Lowe_HF-125.htm
About halfway down the page on the above link is a pic of the board (click to enlarge), it looks to be 560 Ohms. Terry |
11th Feb 2017, 1:36 am | #3 |
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Location: Middlewich, Cheshire, UK. & Winter in the Philippines.
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Re: Lowe HF-125 resistor identification
Yes, looks like 560R
BUT diagonally down right from that resistor is some very dodgy looking soldering! Are they all like that? |
11th Feb 2017, 1:37 am | #4 |
Retired Dormant Member
Join Date: Apr 2016
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Re: Lowe HF-125 resistor identification
Thanks for that, I agree on the 560 Ohm. Very good find.The soldering on mine is nothing like that one thankfully. Karl
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12th Feb 2017, 2:31 am | #5 |
Nonode
Join Date: Oct 2010
Location: Tintinara, South Australia, Australia
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Re: Lowe HF-125 resistor identification
I would be concerned at why it burnt up before replacing it.
Terry |
12th Feb 2017, 11:23 am | #6 |
Dekatron
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
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Re: Lowe HF-125 resistor identification
On Lowe receivers the external keypad socket is 2-pole and provides resistor limited power out to the keypad on the same wire as the data from the keypad comes in.
The keypad 'modulates' the voltage on the data / power line by switching another resistance from the data / power line down to 0V, thereby switching the data / supply line voltage between two levels. A problem on the wiring to the external keypad (ie, short-circuit) might have damaged the receiver's internal limiting resistor. |
13th Feb 2017, 1:20 am | #7 |
Retired Dormant Member
Join Date: Apr 2016
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Re: Lowe HF-125 resistor identification
On further digging it appears that simply plugging in the keyboard plug while the unit is powered can very briefly short the supply line to the keyboard module. The resistor is the weekest link in the chain (thankfully) easy fix and lesson learned. Thankyou to everyone.. Karl
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13th Feb 2017, 11:25 am | #8 |
Rest in Peace
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Re: Lowe HF-125 resistor identification
I agree that R6 looks like 560 ohms but it could be a 56 ohm.
Look at the 3 resistors in the picture below, the one on the right is a cut and paste from another part of the board. The third ring on R6 doesn't look exactly the same as the brown rings or the black rings on the other two resistors. I'm just saying there is an outside chance that R6 is a 56 ohms. You may get a clue from measuring the burnt resistor provided it is not open circuit. |
13th Feb 2017, 1:25 pm | #9 |
Dekatron
Join Date: Nov 2011
Location: Surrey, UK.
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Re: Lowe HF-125 resistor identification
What is the maximum supply voltage present within the receiver? Keyboard control sounds like a 5V sort of thing- even a direct short with 560 ohms wouldn't come near to charring it. Even in a 12V situation, 560 ohms would barely dissipate quarter of a watt (oh, alright, it might be nearer 14V, but it would still be hardly stressed!). 56 ohms sounds more likely, really. 73 ohms sounds believable for a toasted "56" ohm film resistor.
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13th Feb 2017, 1:32 pm | #10 |
Rest in Peace
Join Date: May 2003
Location: Harlaxton, Lincolnshire, UK.
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Re: Lowe HF-125 resistor identification
I had missed that the burnt resistor had been measured at 73 ohms so I agree that it was probably a 56 ohm.
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13th Feb 2017, 2:11 pm | #11 |
Nonode
Join Date: Jan 2010
Location: Edinburgh, UK.
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Re: Lowe HF-125 resistor identification
It would be worth fitting Vero pins to the component holes and mounting the replacement resistor on the pins.
Not only will future replacement be easier, the PCB will be protected from damage. Al
__________________
I won't tell you how I discovered that. |
13th Feb 2017, 7:26 pm | #12 | |
Dekatron
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Location: Newcastle, Tyne and Wear, UK.
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Re: Lowe HF-125 resistor identification
Quote:
This project for the HF-225 nicely illustrates the hardware method employed. http://www.veg.nildram.co.uk/hf225.htm |
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13th Feb 2017, 8:28 pm | #13 |
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Re: Lowe HF-125 resistor identification
The voltage at the resistor is just over 10v and the keypad unit has an 8v regulator on its supply. I have replaced the resistor with a 56ohm and all is working perfect.. Karl
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