Comments on: Multiple DC Voltage Testing Points of Mainboard

By: Jestine Yong

Jestine Yong — Mon, 29 Nov 2021 12:02:01 +0000

In reply to Lynn Blakely.

Hi Lynn,

You can click on this link to read the explanation of nodal impedance.

Jestine

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By: Jestine Yong

Jestine Yong — Mon, 29 Nov 2021 11:55:08 +0000

In reply to Waleed Rishmawi.

Hi Waleed,

You are welcome.

Jestine

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By: Jestine Yong

Jestine Yong — Mon, 29 Nov 2021 11:53:47 +0000

In reply to Yogesh Panchal.

Hi Yogesh,

Yes, very useful to troubleshoot same type of circuit board.

Jestine

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By: Waleed Rishmawi

Waleed Rishmawi — Mon, 29 Nov 2021 08:01:47 +0000

it is like making your own (kind of) schematics with all these test points. yes it is lot of work but at the end it is a time well spent and will cut down on your repair time. that is an excellent idea. thanks for sharing

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By: Yogesh Panchal

Yogesh Panchal — Mon, 29 Nov 2021 07:28:13 +0000

Sir,
Thanks for sharing Tips.This practice is very useful when same type of circuits comes to you for the repair and you have references ready with you.

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By: Jestine Yong

Jestine Yong — Mon, 29 Nov 2021 01:11:39 +0000

In reply to Paris Azis.

Hi Paris,
Amazing! Thanks for your superb explanation!

Jestine

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By: Lynn Blakely

Lynn Blakely — Sun, 28 Nov 2021 21:25:49 +0000

I am enjoying reading all of the article, and all the comments, I don't know the the term "nodal impedance" does it mean a resistance reading for a component to ground?

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By: Paris Azis

Paris Azis — Sun, 28 Nov 2021 17:25:26 +0000

Very interesting article, Jestine, and very controversial the topic among the technicians’ global community, especially as regards these pros and cons...
In any case, troubleshooting any kind of circuit without a schematic is like looking for fleas in the hay...
In such a case and if the device under repair has come for the first time, in my opinion it is not worth it to do all this endless job of keeping such a detailed voltage records. The only exception I see, is the possible very high cost for the owner of the equipment in order to get a new similar replacement, especially if we talk about industrial equipment. In this case, if there is a reasonable agreement with the owner about a proper payment for the intended repair, then is worth it to spend the needed amount of time in order to keep such a record (which could also be used for additional future repairs). Otherwise this effort is meaningless.
I (and many other technicians I guess) happened to make such repairs within this frame of evaluation criteria and with the owners’ agreement.
As regards the methodology itself, I not only agree that it is effective, but also I would say that the more detailed the record the more effective the method is. But, again, under the light of all said above.
Apart from that, I prefer the voltage testing method to be limited in key points of the circuit. In order to do that, a previous analysis of what I have in front of me is necessary. And above all, a thorough visual inspection is of first priority. Also if the circuit is dirty, a proper cleaning of it is the first step. Then the visual inspection follows and finally these specific voltage tests.
I also have got the habit to measure beforehand the power consumption of the device under repair and evaluate the reading carefully. After the repair, I check for any deviations from the first measurement. This is also indicative factor of the effect of the repair itself been done.
Now, in cases that there is expectancy for same devices to come for repairs, then it is worth it to keep detailed voltage records of the circuit.
When working myself with VTRs at the official services of Panasonic and JVC, long ago, I was using a similar alternative method instead of keeping detailed voltage records. I had been using extensively the signature analysis method, using the component tester of the oscilloscope, having a working PCB as reference and comparing any other similar one with it.
The same method is ideally applicable on stereo amplifiers, given that their structure is always symmetrical, that is, the defective channel (and in most cases only one is defective) is a replica of the other. Therefore a “mirror” point by point checking method is very easily implemented and extremely time effective and conclusive.
Personally speaking, I consider the signature analysis method much more conclusive than any other.
If a specific voltage testing method is not clearly successful in finding the culprit component, the signature analysis will surely succeed to spot it.

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By: Jestine Yong

Jestine Yong — Sun, 28 Nov 2021 13:31:31 +0000

In reply to Mark.

Hi Mark,

You are welcome. IC short can be due to overvoltage or surge in the DC supply pin, quality of IC being used, circuit design such as where the IC is position/located (is it located at a component that run quite hot), dry joints in IC leads causing small spark between the leads and the circuit trace and etc.

Jestine

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By: Jestine Yong

Jestine Yong — Sun, 28 Nov 2021 13:24:37 +0000

In reply to Similinga mnyonge.

Hi Similinga,

Good sharing. Yes using nodal impedance and diode reading to test a circuit board is good without have to power it on. One can always check the IC input protection circuitry. Many problems in digital equipment in service are due to damage in the input/output region of the equipment. Having the VI Curve tracer is also an added advantage.

Thanks.

Jestine

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