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Using a logic probe to test an IC

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gkmaia

Member
Is it possible to know just from the pins descriptions bellow what results I should expect from a logic probe?

In terms of low, high or pulse? In order to diagnose if the IC is working?

It's the IC8 Chorus.



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mbarazeen

Member
only steady state logic or slow pulses can be monitored by logic probe.
"just from pins description" you can not check the IC unless it is described in detail on manufacture's maintenance guideline.
 

BusyBee

New Member
In general terms you would need to know the details of the software running to check a working processor system with a logic probe. In some cases it is possible to write test software which effectively holds lines at logic levels for testing, but a very good understanding of the system (as well as ready ability to change system software which is perhaps unlikely here) is required. With some feeling of what is going on though it may be possible to determine if a logic line is being held high or low when it should be changing state.

Tracy
 

dr pepper

Well-Known Member
Most Helpful Member
Its a 3 to 8 line decoder, if you look at the datasheet for it it tells yo waht to expect output wise.
However if the chip runs at any kind of speed, and it probably does you wont learn much from a logic probe, unless you know exactly what the chip is controlling and when.
 

gkmaia

Member
Sorry, I may be asking something very stupid as I am not that experienced.

If I use and oscilloscope (not logic probe) to check the types of signals the IC is sending and receiving I could diagnose if the IC is roughly doing what it is supposed to do or of it is shorted.

For example on VDD , GND and a few other pins I should expect a flatline.
On pins that deal with logic data such as data input , RAM, CPU bus... I should expect squarewaves.

From a generic approach. I don't want to check every function in the IC, but rougly determine if it is sending and receiving readable data from the data pins.

Does that make sense? Sorry as i said I am not that experienced.
 

Pommie

Well-Known Member
Most Helpful Member
A 3 to 8 decoder is normally used to select between different devices (chips) and would normally run at the processor speed. What makes you suspect that particular ic?

Mike.
 

gkmaia

Member
A 3 to 8 decoder is normally used to select between different devices (chips) and would normally run at the processor speed. What makes you suspect that particular ic?

Mike.
That IC controls the Chorus on the Keyboard. When chorus is enabled in the software the sounds gets cracked. When chorus is disabled in the software it sounds perfect.

The chorus IC has also 6 dedicated RAM ICs. I need to check how it communicates with these ICs. The passive components between them have been tested and are fine.

The synth, Reverb, CPU, DAC blocks seem to be working just fine when Chorus is disabled.

I cannot replace that IC, very rare. But I can replace the RAM. But overall it is just a good exercise to learn more about electronics and understand better how to diagnose when you don't have a lot of data available.
 

Pommie

Well-Known Member
Most Helpful Member
It's very unlikely to have anything to do with the 139 chip as that just selects the chorus chip to read/write to it. Do you have the complete schematic that you can post?

Mike.
 
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