Notifications
Clear all

Tech Chat Reading circuit diagrams

Page 1 / 2
 
19Seventie
(@19seventie)
Trusted V-Ratter Registered
Posts: 85

Hi all

I've been repairing and restoring sets for about 3 years or so now but I've always struggled with reading circuit diagrams. I understand the basics like what the symbols mean and things like that, but I tend to get stuck sometimes on what voltages to expect for example. 

I was just wondering if anyone would be willing to give any tips and tricks, and just general pointers to make reading them easier to follow and understand?

(Sorry if not allowed here, it seemed the best place to me)

Thanks
'70

ReplyQuote
Topic starter Posted : 04/01/2022 1:17 am
Nuvistor
(@nuvistor)
Famed V-Ratter Registered
Posts: 4143

@19seventie 

Best to learn some basic theory, ohms law, how valves/ transistors  work etc, then go on to how each stage in the set works. I don’t mean you need to be able to design a set but  the basics of how they work will open up a new world.

Have a look on this sites data library for suitable books, other members may offer other suggestions.

 

ReplyQuote
Posted : 04/01/2022 9:06 am
Cathovisor
(@cathovisor)
Illustrious V-Ratter Registered
Posts: 5789

@19seventie With silicon transistor amplifiers, if you remember the base is always 0.6V higher than the emitter you can soon work out what to expect with a simple application of Ohm's Law.

Amos and James is probably the definitive work on the principles of transistors but a good, broad book is/was Horowitz and Hill.

I learned a lot just from simple study of circuit diagrams - start with a valve radio or three. Some of the pre-war books were very good explaining valve practice - I'll try and dig out some titles for you later.

ReplyQuote
Posted : 04/01/2022 12:48 pm
19Seventie
(@19seventie)
Trusted V-Ratter Registered
Posts: 85

Hi

I've been reading a little bit about ohms law and will continue. I do understand the basic principles of but thats about it. I've got a book on transistors which I've had for a while and do occasionally refer to. Maybe it's time for a proper sit down and re-read of it. It's been a while and when I did read it it went a little bit over my head. I actually forgot I had that book until now!

I didn't know that about the base and emitters, so I'll definitely try and keep that in mind. The book I mentioned is in fact from Amos which was lucky! It's the second edition so will keep an eye out for the first too.

I've learnt a fair bit from just studying sets and their diagrams, but I think that's got me as far as it's going to now. Pre war books sound like they'd be a great introduction as they're probably aimed at those with less experience from the start too!

Thanks
'70

ReplyQuote
Topic starter Posted : 04/01/2022 10:03 pm
crustytv
(@crustytv)
Vrat Founder Admin
Posts: 11262
Posted by: @19seventie

I didn't know that about the base and emitters, so I'll definitely try and keep that in mind

Those of us that did not set out on a career in Radio/Television or even study electronics at school, encounter the same problems you describe. You are lucky having youth on your side, more readily tuned to soaking in new information. I came to this hobby in my mid 40s after a 28-year career in IT. When I was trying to get my head around transistors and testing them, I condensed what I learned about them, into this blog page.  You may or may not find it of use.

Keep at it, it will all start to make sense, these might also be of interest

ohms law

Test a diode

Test a bridge rectifier

Test a Thyristor

p.s.
Another tip I was given and stick to religiously, before anything else, always start with the voltage rails. Get them all understood and working, and where they go to the various circuits stages. You will find this never more so relevant than on the 3000/3500 PSU (I believe you have one still to fix). Where, the 240V, 30V and 58-65V rail interdependencies, are key to it functioning.

 

ReplyQuote
Posted : 04/01/2022 10:29 pm
Red_to_Black
(@red_to_black)
Noble V-Ratter Registered
Posts: 1745

I started in electronics as a hobby when I was in junior school aged about 7 or 8, I started building simple transistor circuits from library books first off using salvaged components from scrap boards, this was a steep learning curve at the time because I had no one to ask, as family didn't understand it, school didn't want to know/or more likely didn't understand it either 🙂

I learnt more by doing stuff on a breadboard (ie. building stuff), thus learning the difference between resistors in series and parallel, capacitors also in series and parallel, PNP and NPN transistor differences, all this was done by a lot of trial and error, probably more error than anything back then.

You have to learn to crawl before you can walk, before you can run so to speak, nobody was born knowing how to read circuit diagrams, it takes a lot of learning, you just have to keep at it.

Electronics/Electrical work has been my lifetime career and I am still learning now and I am still using and reading circuit diagrams daily at work 40 odd years later!.

Even very complex diagrams are just made up of a lot of simpler circuit blocks and subsystems, the key is picking out the salient points and recognisable circuit blocks, not to try to assimilate the whole diagram, especially on complex systems such as TVs and VCRs which to be fair has used some fairly exotic circuitry over the years.

ReplyQuote
Posted : 04/01/2022 10:55 pm
Sundog
(@sundog)
Trusted V-Ratter Registered
Posts: 161

Let's not forget that there are also different conventions. There are at least 2 ways of drawing connection wires' crossing and their junctions, and multiple ways of drawing component symbols.

When one looks at schematics from different decades and countries it must be confusing for a beginner.

Don't be put off though, it has kept my interest for over 60 years, and I hope for some more!

ReplyQuote
Posted : 05/01/2022 8:55 pm
Red_to_Black
(@red_to_black)
Noble V-Ratter Registered
Posts: 1745

@Sundog 

Tell me about it! some Philips and Thomson diagrams were difficult at first, Panasonic and Sony diagrams had a strange way of depicting similar things!, Salora and B&O could be a law unto themselves.

When you start to get into industrial diagrams you might think things would change and be more standardised?, not a bit of it! although we are supposed to be following 'global standards' every designer and/or the particular software package the different manufactures use now can be very different depending whom you work for at any given point in time.

The point I was trying to get across to 1970 was don't be dis-heartened Rome wasn't built in a day 🙂

ReplyQuote
Posted : 05/01/2022 11:39 pm
19Seventie
(@19seventie)
Trusted V-Ratter Registered
Posts: 85

Thank you for those links crusty, I'll definitely check those out after, they should definitely be of help to me. That's right about the 3000 I have, I'm hoping to be able to use it as a learning exercise rather than my old method of replacing suspect components and seeing if it makes a difference or not. That method works but it's a lot of faffing about when it could be done better. The 3000 and its PSU should be a great set to use just on the sheer amount of information devoted to one section of one set. 

I did think about building things, such as audio amplifiers, but have never gone on to do so, I've stuck to completing pre-existing repair projects but maybe I should look into building some basic things to get a bit of an idea and not have to worry about ruining things. I think that has held me back a bit too, where I'm repairing things I tend not to experiment too much as I don't want to risk further damage. 

I think that I'm actually okay with recognising symbols in circuit diagrams, I'm sorta used to that part, for me it's more following traces and knowing what to expect and what part of the circuit diagram is which. I can of course trace back from say the speaker to the sound sections, but i struggle to know where it starts, for example. 

I think my main hold up is knowing whether traces are coming or going (so to speak) and, like i said, which voltages to expect where there's several along a trace on the diagram, but im sure with the help given here and more experience ill come to get to know what to expect and the likes. 

EDIT: Posts crossed with Red to Black. Maybe I don't know symbols and depictions as well as I thought then! Luckily I've not come across any that have symbols and stuff thats confused me. But then again diagrams just confuse me as a whole, that's why we're here! 🤣 

Thanks all
'70

ReplyQuote
Topic starter Posted : 05/01/2022 11:39 pm
Cathovisor
(@cathovisor)
Illustrious V-Ratter Registered
Posts: 5789
Posted by: @red_to_black

Tell me about it! some Philips and Thomson diagrams were difficult at first, Panasonic and Sony diagrams had a strange way of depicting similar things!, Salora and B&O could be a law unto themselves.

The various ways of drawing transistors could be fun - and don't get me started on the notation for logic gates!

Wasn't this

transistor

the European standard symbol for a transistor? That's taken from a Leak amplifier manual.

ReplyQuote
Posted : 06/01/2022 2:12 pm
Katie Bush
(@katie-bush)
Illustrious V-Ratter Moderator
Posts: 5150
Posted by: @cathovisor

@19seventie With silicon transistor amplifiers, if you remember the base is always 0.6V higher than the emitter you can soon work out what to expect with a simple application of Ohm's Law.

Oh, now, what was that little line I once heard, many, many moons ago? - Something along the lines "My 'sister goes point six, Base over Emitter when her Collector comes to call". I'm not a hundred percent sure quite how it was worded.

ReplyQuote
Posted : 06/01/2022 3:13 pm
Boater Sam
(@boater-sam)
Reputable V-Ratter Registered
Posts: 413

I have been reading circuits for..................62 years! Heck, I'm so old.

I am fine with most but the American sideways valve drawing still causes me some angst.

I find the block IC diagrams lack information but as the chips are too small for me to read the numbers now it matters little.

ReplyQuote
Posted : 06/01/2022 6:05 pm
Sundog
(@sundog)
Trusted V-Ratter Registered
Posts: 161

I'll throw in some more confusion - nomenclature - not exhaustive by any means.

Transistor: T, Tr, Q, V, Vt,

Valve: V, Vt

CRT: V, Vt, Q, 

Diode: D, M, Mr, Br, Vd, 

LED: D, LED, 

Varicap diode: D, BB, ,

Zener diode: D, Z, ZD,

Integrated circuit: IC, I, 

Inductor: L,

Variable inductor: L,

Resistor: R,

Potentiometer: R, P, Vr, 

Capacitor: C, 

Variable Capacitor: C, Vc, 

Transformer: T, Tr,

Relay: RL, RLA, K,

Solenoid: L, K,

Loudspeaker: L, Ls, Sp, 

Crystal: X,

Switch: Sw, S, 

Connector: Cn, J, C, X, P, U, K, Sk, 

Supply lines -ve, +ve, LT, HT, +B, HV, EHT, 

Just for some fun, for those who haven't seen it:

circuit diagram

 

ReplyQuote
Posted : 06/01/2022 7:40 pm
Cathovisor
(@cathovisor)
Illustrious V-Ratter Registered
Posts: 5789

@sundog Fairly sure I've seen "W" used against a transistor before now.

ReplyQuote
Posted : 06/01/2022 9:17 pm
Sundog
(@sundog)
Trusted V-Ratter Registered
Posts: 161

Yes, I guess that must be well known on this forum: Thorn I believe.

I wonder what made them choose W.

ReplyQuote
Posted : 06/01/2022 9:45 pm
19Seventie
(@19seventie)
Trusted V-Ratter Registered
Posts: 85

@katie-bush 

I'll have to remember that little rhyme! Plenty of rhymes I used in school that I still use to this day so should stick! 

@boater-sam

The best I can do with IC's are measure voltages on the pins and take a punt at whether it's good or not, usually using other information like stock fault lists etc. (PS i forgot to say, I love your barker 88 profile picture, i've got one here waiting restoration too)

@sundog

I've actually taken a screenshot of that and will keep it in my electrical help folder on my PC, things like that are certainly handy to refer back to for me, and I'm sure many others too! Thank you

Funnily enough could make some sense of most of the diagram you sent! 

Thanks again all! Really appreciate the help!
'70

ReplyQuote
Topic starter Posted : 06/01/2022 11:41 pm
Jayceebee
(@jayceebee)
Noble V-Ratter Registered
Posts: 1623
Posted by: @sundog

I wonder what made them choose W.

I’ve always wondered if it came from Westector?

ReplyQuote
Posted : 06/01/2022 11:49 pm
mfd70
(@mfd70)
Active V-Ratter Registered
Posts: 228

One thing to remember when reading voltages in vintage electronics, which often catches me out, is the Fluke true RMS meter (or equivalent) you are using would be more accurate and have a higher input impedance than anything in existence outside a research lab back then. Voltages can be out by quite a bit from the stated values in the manual and not effect the operation of the circuit. Old British TV and monitor manuals from as recently as the eighties would state that the voltage readings were measured with an AVO 8 and we always had a "good" AVO in the workshop for voltage checks.

ReplyQuote
Posted : 07/01/2022 1:01 pm
Sundog
(@sundog)
Trusted V-Ratter Registered
Posts: 161

@mfd70 Indeed 20KΩ/Volt was the standard then for taking DC measurements.

ReplyQuote
Posted : 07/01/2022 1:06 pm
Sundog
(@sundog)
Trusted V-Ratter Registered
Posts: 161

@jayceebee Perhaps. I can't think of anything better.

ReplyQuote
Posted : 07/01/2022 1:11 pm
Page 1 / 2