Author Topic: Display has wrong SMD resistor  (Read 3493 times)

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Offline HighInBC

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Display has wrong SMD resistor
« on: October 18, 2015, 05:50:48 pm »
I have a "Grove LCD RGB Backlight" 2x16 display. Rather than having a potentiometer to adjust the contrast like most LCD 2x16 displays they decided to put in a 1K resistor(R7). I am not sure what they were thinking but for this particular unit it made the contrast so light it was not readable.

I have already managed to fix it by removing the 1K ohm resistor and replacing it with a through hole 220 ohm resisitor:



My repair works fine but it is ugly and delicate.

I think the part I replaced was a 0603 resistor. Is it practical to replace it with the correct part? Can this be done with an iron or do I need special tools?

I described the details of the method I used at Fixing the contrast on a Grove LCD RGB Backlight. Is there a better way to do this?
 

Offline wblock

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Re: Display has wrong SMD resistor
« Reply #1 on: October 18, 2015, 06:10:44 pm »
My repair works fine but it is ugly and delicate.

I think the part I replaced was a 0603 resistor. Is it practical to replace it with the correct part? Can this be done with an iron or do I need special tools?

You've already done the hard part, removing the old one.  Soldering on a new resistor should not be too bad, other than dealing with the small size.  An iron will work fine.
 

Offline HighInBC

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Re: Display has wrong SMD resistor
« Reply #2 on: October 18, 2015, 06:15:03 pm »
You've already done the hard part, removing the old one.  Soldering on a new resistor should not be too bad, other than dealing with the small size.  An iron will work fine.

All I did was press gently on it with the iron while applying a liberal amount of fresh solder. That was the easy part, took about 2 seconds. In the past I have had a terrible time trying to heat both ends at the same time, but since I figured out to add solder it is easy breezy.

I am going to order some 0603 220 ohm resistors and see what I can do. Worst case scenario I end up breaking it again.

Thanks for the response. I have been reading this forum for a while, but just signed up.
 

Offline wblock

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Re: Display has wrong SMD resistor
« Reply #3 on: October 18, 2015, 06:21:55 pm »
All I did was press gently on it with the iron while applying a liberal amount of fresh solder. That was the easy part, took about 2 seconds. In the past I have had a terrible time trying to heat both ends at the same time, but since I figured out to add solder it is easy breezy.

It can be a fight.  Two irons can help, or even special-use tweezers: http://www.jbctools.com/pa120-a-micro-tweezers-product-49-category-5-menu-2.html.

Quote
I am going to order some 0603 220 ohm resistors and see what I can do. Worst case scenario I end up breaking it again.

Get several.  They are small and easy to lose.  You might also consider soldering wires to those pads and running them to an external potentiometer in case the contrast needs to be changed due to viewing angle or backlight color.

Quote
Thanks for the response. I have been reading this forum for a while, but just signed up.

I'm fairly new here, too. :)
 

Offline HighInBC

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Re: Display has wrong SMD resistor
« Reply #4 on: October 18, 2015, 06:26:15 pm »
If you just smother the resistor in a solder blob, this melts both sides at the same time and it pops off quick and easy. I would only do this with solder mask in place, but that is the norm with SMD parts.

I was not planning on ordering just one 0603 resistor, they are 100 for $1 on a popular auction site. With electronics I pretty much always buy way more than I need, the stuff is so cheap and it takes forever to come from China so I like to have a stash of parts. I have it in 0805, but of course they used a different size.

I did consider a potentiometer, but I will have to decide where the screen will be mounted before I add that, needs to be well anchored so it does not put stress on the pads.
« Last Edit: October 18, 2015, 06:28:07 pm by HighInBC »
 

Offline tggzzz

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Re: Display has wrong SMD resistor
« Reply #5 on: October 18, 2015, 06:36:19 pm »
I am going to order some 0603 220 ohm resistors and see what I can do. Worst case scenario I end up breaking it again.

Quite frankly you might as well order a complete set of them, and be done with it. Compare the prices for individual resistors (even 25 off!) with http://www.ebay.co.uk/itm/0603-SMD-1-KIT-RESISTOR-E-24-SERIE-153-VALUES-x-25pcs-/171701000268

Make sure they are well marked! You can also pay extra and get them in books.

Same goes for capacitors
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Offline Mechatrommer

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Re: Display has wrong SMD resistor
« Reply #6 on: October 18, 2015, 06:47:29 pm »
I think the part I replaced was a 0603 resistor. Is it practical to replace it with the correct part?
what about connecting it to 2 wires to a potentiometer glued somewhere, so later you can adjust the contrast without changing part.
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Offline HighInBC

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Re: Display has wrong SMD resistor
« Reply #7 on: October 18, 2015, 06:54:12 pm »
Quite frankly you might as well order a complete set of them, and be done with it....

That is a good idea. I will do that. You can never have too many parts.
 

Online mikerj

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Re: Display has wrong SMD resistor
« Reply #8 on: October 18, 2015, 07:09:11 pm »
I have a "Grove LCD RGB Backlight" 2x16 display. Rather than having a potentiometer to adjust the contrast like most LCD 2x16 displays they decided to put in a 1K resistor(R7). I am not sure what they were thinking but for this particular unit it made the contrast so light it was not readable.

I've never seen a LCD-character module with a built in potentiometer for contrast. Normally you provide the contrast voltage to one of the pins on the connector using an external voltage source (e.g. potentiometer or DAC).
 

Offline HighInBC

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Re: Display has wrong SMD resistor
« Reply #9 on: October 18, 2015, 07:21:17 pm »
I have a "Grove LCD RGB Backlight" 2x16 display. Rather than having a potentiometer to adjust the contrast like most LCD 2x16 displays they decided to put in a 1K resistor(R7). I am not sure what they were thinking but for this particular unit it made the contrast so light it was not readable.

I've never seen a LCD-character module with a built in potentiometer for contrast. Normally you provide the contrast voltage to one of the pins on the connector using an external voltage source (e.g. potentiometer or DAC).

You make a good point. What I meant was that an I2C controller for such screens generally have a pot, and that the screens have a pin for that. What I thought was odd is that they put in a static resistor instead of making it available. Basically you need a way to adjust it, and they did not provide that.

This was advertised as a complete solution ready to go without external parts so that is why I expected a pot to be installed in it.
« Last Edit: October 18, 2015, 07:28:20 pm by HighInBC »
 

Offline tooki

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Re: Display has wrong SMD resistor
« Reply #10 on: October 19, 2015, 01:14:00 am »
It's also a pity they didn't just make contrast software-controllable as it is in, for example, those Nokia 5110 LCDs.
 

Offline crispy_tofu

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Re: Display has wrong SMD resistor
« Reply #11 on: October 19, 2015, 02:44:15 am »
I think the part I replaced was a 0603 resistor. Is it practical to replace it with the correct part?
what about connecting it to 2 wires to a potentiometer glued somewhere, so later you can adjust the contrast without changing part.

Maybe one of those little SMD trimpots (if the range is far enough and size is small enough)  ;D
 

Offline Rasz

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Re: Display has wrong SMD resistor
« Reply #12 on: October 19, 2015, 04:00:21 am »
why bother? it works now. Do you  intend mounting it in a mountain bike(shock/shakes)?
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Offline HighInBC

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Re: Display has wrong SMD resistor
« Reply #13 on: October 19, 2015, 04:28:05 am »
why bother? it works now. Do you  intend mounting it in a mountain bike(shock/shakes)?

I agree this is good enough for use. This will probably be the display for the reflow oven I am working on. I would like to learn to replace 0603s at some point though.
 

Online TheSteve

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Re: Display has wrong SMD resistor
« Reply #14 on: October 19, 2015, 06:17:31 am »
why bother? it works now. Do you  intend mounting it in a mountain bike(shock/shakes)?

I agree this is good enough for use. This will probably be the display for the reflow oven I am working on. I would like to learn to replace 0603s at some point though.

Some good tweezers and an old board to practice on and you'll be able to swap them no problem. Nothing more then a regular soldering iron, tweezers and some solder wick(optional) is all that is needed.
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