Help - What does 10 mean resistor schematic???

Thread Starter

ColoradoRobert

Joined Jan 22, 2016
155
I've got a guitar amp that stopped working and when I took it apart I found 2 resistors and 1 chip had fried. I was able to locate the replacement chip but after searching the schematic on the 2 resistors all they read is "10." I have attached the schematic = R215 is at C6 - R61 is at A6 both on page 3. I just need to know what to order. Thanks in advance.
 

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Thread Starter

ColoradoRobert

Joined Jan 22, 2016
155
That's why I asked the question because there are electronics people here. No k behind the 10 seems to mean 10ohm but I'd like to get peoples opinion especially with possible wattage voltage considerations, etc.
 

LesJones

Joined Jan 8, 2017
2,698
They are 10 ohm resistors and they connect different parts of the ground system together. If they have fried then it is probably due to this piece of equipmet being connected to another piece of equipment that had a different potential on it's ground. Check that the ground wire on your amplifier is connected properly. If that is OK then try to remember what equipment was connected to your amplifier before it failed. If you can remember than check the earthing on that equipment.

Les.
 

Reloadron

Joined Jan 15, 2015
5,646
They look to be 10 Ohm resistors. R215 is part of a Ground Lift circuit:
In sound recording and reproduction, ground lift or earth lift is a technique used to reduce or eliminate ground-related noise which is done by connecting signal lines between two or more pieces of equipment so ground loop is established. It interrupts the ground line at some point. It is particularly effective at eliminating ground loops, but it may also increase or decrease noise from other sources.
My guess is a ground issue caused the problem. The cooked resistor is a symptom, unless the root cause is found or known replacing the resistors will likely result in more toasted resistors. Using a low value 10 Ohm resistor for a ground lift would make sense so my vote is 10 Ohms. :)

Ron

Oh well, late as Les beat me to it.
 

Thread Starter

ColoradoRobert

Joined Jan 22, 2016
155
Hope someone will respond to this old post of mine. Checking this amp more with what I have (little knowledge and test equipment),
I ran across opamp U9. Across the bottom of Page 1 of the attached schematic at A5 - U9 opamp seems messed up.

First, let me explain how I read these (remember very-novice). On the pre-amp (page 1 & 2) there are only 3 different sets of opamps.
All have 8 pins or 4 pair across. With my ohm meter (in circuit unsoldered) reading across the pairs all read something, except the 1 pair
on U9. It is dead no matter what combination I make. You can also see U9 on page 2 at 3D. What is your opinion of this? When I goggle the
number CA3080AE, Mouser comes up and shows it but says, "obsolete." They don't give you a direct replacement. I wish they would
because I find their search function hard to use. Do you know how to find a replacement?
 

MrChips

Joined Oct 2, 2009
21,918
Hope someone will respond to this old post of mine. Checking this amp more with what I have (little knowledge and test equipment),
I ran across opamp U9. Across the bottom of Page 1 of the attached schematic at A5 - U9 opamp seems messed up.

First, let me explain how I read these (remember very-novice). On the pre-amp (page 1 & 2) there are only 3 different sets of opamps.
All have 8 pins or 4 pair across. With my ohm meter (in circuit unsoldered) reading across the pairs all read something, except the 1 pair
on U9. It is dead no matter what combination I make. You can also see U9 on page 2 at 3D. What is your opinion of this? When I goggle the
number CA3080AE, Mouser comes up and shows it but says, "obsolete." They don't give you a direct replacement. I wish they would
because I find their search function hard to use. Do you know how to find a replacement?
You cannot test an op-amp (or any IC for that matter) by testing for resistance across any pins, in-circuit or out-of-circuit. Period.
 

Thread Starter

ColoradoRobert

Joined Jan 22, 2016
155
I find that hard to believe but you probably know more than I do. For an argument though, if I have two brand new opamps, exactly the same as the one I feel is bad.... and I read with my ohm meter and compare them and there is a difference doesn't that prove something. Other than it's not the traditional way to test these? BTW, MrChips can you tell me what opamp to replace this one with, since it is obsolete?
 

AnalogKid

Joined Aug 1, 2013
8,608
https://www.intersil.com/content/dam/Intersil/documents/ca30/ca3080-a.pdf

The 3080 at the bottom of the page shows the power connections. The real opamp is located lower center, B5, pointed to the left. This is not a normal opamp, it is an OTA (operational transconductance amplifier). It is used as a variable-gain amp; its gain depends on a control voltage or current fed into pin 5. It looks like this amp has a semi-smart compressor to protect the power amp and speakers. National, ADI, and THAT make VGAs, but not as drop-in replacements for this part.

Ask around on this and other fora. I don't have any of these, but lots of geezers have lots of old parts. Many will send them out for the cost of the shipping.

Digi-Key's parametric search engine is better.

ak
 

Thread Starter

ColoradoRobert

Joined Jan 22, 2016
155
Thank you for the reply AnalogKid. I will keep that handy when I call into Digi or Mouser because I did not know any of that. I did suspect it was different since it was the only one. So maybe my theory is really-wrong = there could be two dead pins and they will not show like all the others, especially the way I am checking them.
 
Last edited:

MrChips

Joined Oct 2, 2009
21,918
I find that hard to believe but you probably know more than I do. For an argument though, if I have two brand new opamps, exactly the same as the one I feel is bad.... and I read with my ohm meter and compare them and there is a difference doesn't that prove something. Other than it's not the traditional way to test these? BTW, MrChips can you tell me what opamp to replace this one with, since it is obsolete?
There is a company that makes a piece of equipment that performs tests along those lines, known as analog signature analysis. One would compare test points on a bad board with those of a good board. Typically, companies would give this task to technicians who know little (and need to know little) about how the circuit functions. I call it a crapshoot.
 

dl324

Joined Mar 30, 2015
11,593
if I have two brand new opamps, exactly the same as the one I feel is bad.... and I read with my ohm meter and compare them and there is a difference doesn't that prove something.
It proves nothing. To test an integrated circuit, you need to apply power and use an appropriate circuit to test them.

The only thing you can measure on an unpowered IC are the input protection diodes, if they exist. Functioning protection diodes doesn't mean functioning IC...

Use your common sense. Can you tell if an appliance functions without powering it and turning it on? Can you tell if a car functions if you don't start it?
 

Thread Starter

ColoradoRobert

Joined Jan 22, 2016
155
Chatted with Digi (techs are gone at Mouser) and they said, "we do not offer a replacement... look on ebay." I see them there in China (up to 20 days delivery), so maybe that is my best choice; if this is bad. If not, another 6 bucks gone.
 

Thread Starter

ColoradoRobert

Joined Jan 22, 2016
155
There is a company that makes a piece of equipment that performs tests along those lines, known as analog signature analysis. One would compare test points on a bad board with those of a good board. Typically, companies would give this task to technicians who know little (and need to know little) about how the circuit functions. I call it a crapshoot.
Crapshoot for some for me it's a future. Lol
 

dl324

Joined Mar 30, 2015
11,593
I see them there in China (up to 20 days delivery), so maybe that is my best choice; if this is bad. If not, another 6 bucks gone.
That's probably your worst choice. Some companies sell salvaged components that they clean up; with no consideration for functionality. They may also take some generic opamp and relabel as a more exotic CA3080.
 
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