Working out resistor value from the colour coded bands

Thread Starter

Acerman

Joined May 30, 2019
16
I have a Yamaha Keyboard which I have owned for 25 years. I noticed recently that although some functions still work the actual keys are playing the wrong notes and some are not playing atall. I opened up the keyboard yesterday and discovered some badly damaged resistors. It looks as though battery acid has seeped in and corroded the resistors. However the majority of them are ok. I need to replace about 10 resistors. They all have identical colour coding . I have been trying to work out the value of resistor that I need to get. The photo shows the colour code of the resistors. I worked out that they are 1kohm. 5 x2 x a 100 multiplier value. I go that from red times green times a red multiplier which is 100. Do people agree. If not what is the value of these resistors?
 

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jpanhalt

Joined Jan 18, 2008
11,088
The bands on resistors are read sequentially as digits, not multipliers. The exception is the multiplier band. A 1 k resistor (4 band) is brown, black, red = 1,0,x 10^2 + tolerance = 1 0 00 Ω + tolerance.

I am not sure what you show are resistors. They may be diodes or something similar (e.g., zener diodes) in glass. The green may be a polarity marker. A clear picture will help. You can remove one end of one and test it.

EDIT:

Sharpened with very old CS3 PS version:
1592561907829.png
 
Last edited:

Thread Starter

Acerman

Joined May 30, 2019
16
The bands on resistors are read sequentially as digits, not multipliers. The exception is the multiplier band. A 1 k resistor (4 band) is brown, black, red = 1,0,x 10^2 + tolerance = 1 0 00 Ω + tolerance.

I am not sure what you show are resistors. They may be diodes or something similar (e.g., zener diodes) in glass. The green may be a polarity marker. A clear picture will help. You can remove one end of one and test it.

EDIT:

Sharpened with very old CS3 PS version:
View attachment 210141
Thanks for your response. I thought that they were resistors.Possibly diodes? Thats interesting. It would probably be eaier to replace these if they are diodes. They do seem to be made of glass.
 

jpanhalt

Joined Jan 18, 2008
11,088
I would certainly test them before replacing them.

It seems to be popular to replace capacitors, resistors, and diodes without knowing they are actually defective. There are actually whole sites devoted to "recapping." I don't think that is a good practice. One not infrequently sees visitors here who have damaged something else in the the process, such as damaging a plated through hole in a via/pad or PCB trace.

The area you show does not look damaged. Can you post clear pictures of the damaged areas? Where would "battery acid" come from? Is the keyboard battery operated? What type of battery is/was used?
 

Thread Starter

Acerman

Joined May 30, 2019
16
Only a limited number are damaged. It is only the ones that are directly affected by the battery acid. I have attached a new photo to show the affected ones. One of them disintegrated when I touched it with the DMM probes.
The Yamaha keyboard can be used by mains but also has a battery operation option. Normal standard batteries that you can buy anywhere (D size). The keyboard has a battery compartment so that it can be used as a portable device. I left some batteries in by mistake and they leaked. The battery compartment is now ruined and very corroded .
 

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sagor

Joined Mar 10, 2019
421
Those all seem to be small signal diodes. They would be used in some form of keyboard matrix to detect which key is pressed.
Remove one of the "good" ones and check with an ohm meter in Diode function that it conducts in one direction only. It should show a voltage drop around 0.5V to 0.7V.
Hard to tell the size of these, but a common small signal diode is the 1N4148.

Good luck
 

Thread Starter

Acerman

Joined May 30, 2019
16
Those all seem to be small signal diodes. They would be used in some form of keyboard matrix to detect which key is pressed.
Remove one of the "good" ones and check with an ohm meter in Diode function that it conducts in one direction only. It should show a voltage drop around 0.5V to 0.7V.
Hard to tell the size of these, but a common small signal diode is the 1N4148.

Good luck
Thanks Sagor for the useful advice. As long as i get the correct replacement components I should be able to get this working again cheaply. It has mini keys and is very useful to me. I had a quick look on ebay and a lot of them are rated at 12 volts. Would those be any good or is the 1N4148 the one to go for?
 

Thread Starter

Acerman

Joined May 30, 2019
16
Go for the 1N4148 from a reliable source. They're inexpensive.
Thank -you. This has solved my problem and hopefully I can get the old girl working again. I have a busy few days ahead but this time next week I may have the time to sort it.
 
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