Newbie Question Schematics reference resistance measurements

[Lisa_k]

Hi There
I am new to learning how to read schematics and have seen a few videos on the subject where people have spoken about how manuals have given reference resistance values but never really elaborated on how to check them.

I'm sorry if this has been asked before, I've made a search, perhaps I am using incorrect terms

I have a sony service manual with reference measurements, would I be right in thinking a measurement from pin 14 and pin 25 would get 1.4k?

[sam_sam_sam]

Re: Newbie Question Schematics reference resistance measurements

For me to give you a better answer you need to show the hole page and show what note #2 says
Because I do not want to assume anything because I have not seen all of the page

No it not something that is widely known if you have just started learning how to troubleshooting from a circuit diagram

But usually there is something in the notes somewhere in this manual if the manual is worth a crap should tell you this at least the ones I have run across but you will have to maybe go through the manual to find this information

Sometimes they will tell you that certain switches might have to be in the ON or OFF position or whatever that position might be if it is a selector switch with more than two positions

Sometimes you will see where it will tell which way the meter leads needs to be to get the results that they are telling you

But generally speaking the reference is ground but not always

[Lisa_k]

Re: Newbie Question Schematics reference resistance measurements

Thank you for your reply it was most helpful.
From what I gather with what you have suggested and with what I have in the manual (page 5 section 2) the resistance is measured with respect to ground under no load.

I could be mistaken but note 2 is in relation to the sine wave that is output

I can share the service manual if that is alright to do so?
If not there are a few copies of it online under the name of Sony-PS-DJ9000-Service-Manual.pdf

In any case I have attached the notes for the schematic diagram


Thanks again

[jons]

Re: Newbie Question Schematics reference resistance measurements

Those are dc voltage not resistance readings.

[sam_sam_sam]

Re: Newbie Question Schematics reference resistance measurements

Those are dc voltage not resistance readings.

Voltage reading are the norm but I have seen in some manuals with resistance reading as well that is why it is important to find the page that you posted to know what you are measuring

This is a very important thing to keep in mind when you are comparing your measurements and comparing your results

“ Voltages are taken with a VOM (Input impedance 10 Ms2).
Voltage variations may be noted due to normal production tolerances.”

I have not seen “Ms2” so I not sure exactly what this is someone else needs to chime in to what this means

[eccerr0r]

Re: Newbie Question Schematics reference resistance measurements

In service manuals it's typical to print expected voltages near wires with an arrow or using a different color font. There is no standard for this so expecting to learn from examples, you really need a lot of examples, as well as read the rest of the manual (usually printed on the same page but not always) that describes what the voltages are and what conditions are needed to get that voltage on a working device.

Also yes voltages may be off a bit but still be okay. To know requires a bit of experience.

Ms2 means MΩ except someone cheesed the font.

[Lisa_k]

Re: Newbie Question Schematics reference resistance measurements

Thank you to everyone that has helped. I think you are all right. I was hopefull that it wasn't voltage, as measuring voltage whilst the unit is on is quite intimidating.

Here is the schematic


I will measure for volts, but would any ground do?

[R_J]

Re: Newbie Question Schematics reference resistance measurements

Be careful around the A/C input, but after the transformer the voltage is a lot lower (25v & 12v), It looks like any ground would do, Page 7 shows a good ground point (eyelet marked E)
You could provide the problem with the turntable, then we could help you better.

[Lisa_k]

Re: Newbie Question Schematics reference resistance measurements

Be careful around the A/C input, but after the transformer the voltage is a lot lower (25v & 12v), It looks like any ground would do, Page 7 shows a good ground point (eyelet marked E)
You could provide the problem with the turntable, then we could help you better.

hi there,
I've avoided any AC transformers or any huge caps and tried to keep near the IC's


The turntable itself works great, although I noticed that the platter jutts forward when powered on and that the strobe drifts forwards with quartz lock enabled.
I can make it very stable with the pitch fader however.


A few strange measurements on IC2 (ic9242) apc and afc were way off. I noticed the resistors are spec'd at 150k but my DMM reads under 60k

I also noticed the dc motor driver ic01 (Ta7259p) has lower +vin then spec'd (1.1 instead of 2.2)

As I was tracing along the board i noticed lots of ceramic caps that look like they have been hacked on, it was at this moment i realised I was out of my league on this one. I think i will leave it be as its mostly working correctly.

but a massive thanks to everyone that has reached out I got over my fear of taking a voltage when powered on which was a huge win with all your help

[Crystaleyes]

Re: Newbie Question Schematics reference resistance measurements

hi there,


I noticed the resistors are spec'd at 150k but my DMM reads under 60k

For future reference, remember to desolder and lift one leg of resistors in order to get an accurate measurement, as often they are in parallel with other resistors or components which will affect your readings.