Measuring component readings

[Jonathan Wilcox]

I'm fixing a turntable and want to know how to test individual components on a circuit board. Can anyone advise me on what are the most important parts to test and how?

I have watched a few videos and have figured I need my multimeter on diode mode, wires on pos/neg and reading should be between 0.3 - 0.7 but that's about all.

Also what does it mean if a diode is below or above reading?

 

[StephenRowley]

You need the circuit digram for the RP or at least a decent idea of the general wiring layout of it. Also it not simple as measuring with the values of invidual components in circuit as there values won't tally with their rating when in circuit.

You need to test it while powered up which brings the whole danger associated with 240v supplies.

Then you need your circuit digram measure voltage rails and possibly an oscillascope to trace the signal path.

 

[littlespark]

Try an electronics forum. This is more for electricians.
Saying that, someone here might have a clue.

This is your business? Fixing turntables?

 

[Wilko]

Hi JW and welcome to the Forum.

Yes, tell us a bit more about what's happening, what equipment you've got etc. Testing components is not easy when they are still mounted on a circuit board but I would not be unsoldering thing to measure them as a first step. I start with the manufacturer's circuit diagram and use their indicated test points. 3.7V at tp1 etc.

 

[SparkyChick]

It's also worth mentioning 'bad caps' just in case you've never heard the term before.

It relates to the failure of some capacitors and usually manifests itself as bulging or leaking aluminium cans. If you Google 'bad electrolytic capacitors' you'll get a wealth of information.

I've rescued many items of home electronics and computer gear just by changing out the affected parts.

But as @Wilko says, please tell us a bit more about the problems you're having.

 

[Lucien Nunes]

To troubleshoot electronics effectively, you need a reasonable knowledge of how the circuit works and what signals and voltages to expect at various important points. Faultfinding by testing individual parts is slow, likely to miss the root cause of many faults, and may not find a fault at all. Individual component tests are mainly used once the fault is localised, to confirm a diagnosis and to identify the extent of the damage where multiple parts are affected, in which case the parts under test are likely to need replacing anyway.

Testing in-circuit vs. disconnecting parts depends on the influence of each part on others around it. For example, a resistor shunted only by a polyester cap can be tested in-situ without caveats. One shunted by a BE junction of a transistor may be testable according to the value of the resistor and the nature of the transistor. One shunted by a transformer winding probably can't be tested in situ.

What is your specific problem with diodes here? TT Model? Symptoms? Readings?

FWIW there is a good vintage electronics forum concerned mainly with radio/audio/TV, where there is a wealth of knowledge and experience and no bull/audiophoolery. UK Vintage Radio Repair and Restoration Discussion Forum - https://www.vintage-radio.net/forum/

 

[Jonathan Wilcox]

Hey guys,

Thanks for all your responses. No problems to report; I'm comfortable exchanging all the parts with advice from qualified electricians.

I am asking as I would like to notify clients of any soon-to-blow components and also to ensure I am swapping out the correct part if an unknown issue was to occur - I just want to be prepared really.

I currently have everything needed to repair a turntable really apart from expensive oscillators and reflow ovens. At the moment I'm using a cheap multimeter, lead-free solder, a soldering iron with a stand (reaching 350F) rosin paste for flux, a wet sponge to wipe soldering iron, solder sucker. Lots of other equip like iso alcohol for cleaning and lubricating.

I guess I'd like to find a guide that will show me how to test for the culprit, which also shows me what the expected readings of healthy components are. I'm trying to find a circuit diagram for a technic 1210 turntable but finding it difficult.

Thanks for the form links! and yes it is my part time occupation alongside digital marketing! the joys....

 

[static zap]

Spotted an ebayer -offering a pcb upgrade.
" -Updated mother board ICs removing faults with older models, torque issues and inconsistent rpm."
May be some clues with the parts he uses .. never quite go into modern turntables ... Weirded out by Amstrad ? linear one !

 

[Lucien Nunes]

I guess I'd like to find a guide that will show me how to test for the culprit, which also shows me what the expected readings of healthy components are

I don't think there's a single book that will tell you all of that. Good troubleshooting and preventative maintenance requires a synergy of knowledge (maths, physics, electronic theory, rote learning of facts and figures), experience (familiarity with strengths and weaknesses of different parts, different circuit designs, typical behaviour modes) and insight (obscure chains of cause and effect, reconciling incompatible or impossible evidence, recognising your own errors and false conclusions).

To make things easier for people unfamiliar with specific models, manufacturers sometimes provided troubleshooting flowcharts or blow-by-blow circuit descriptions as part of the service information. They will give you instructions like: 'Check for 2.6-3.0V p-p sawtooth at TR3 emitter. If low or missing, check TR3, 4, R12 and proceed to step 17.' This helps to fast-track to any of the most likely faults that the manufacturer could foresee, but they are specific to individual models. With experience, waveforms and voltages shown on a schematic are usually sufficient to understand what should be going on, so that you can draw your own conclusions if it is not.

There is the 'brute force' repair method of changing all likely bad / life-expired parts, in the hope that any faults will be amongst them. This teaches you nothing about faultfinding and electronics but if the faults are mainly of one kind you can get quite good success rates. This doesn't work for more complex pieces of kit because a) you might have to change a thousand parts, b) you tend to create additional faults as you work, and c) the completed device might then need setting up from scratch, requiring as much knowledge as troubleshooting it properly in the first place.

Not trying to rain on your parade but there is no shortcut to what is a complex skill and craft. I've been doing it daily for 30 years and I have a hell of a lot to learn.

Do you mean Technics SL-1210? I found a schematic in 10 seconds....

 

[Jonathan Wilcox]

Yes, Technics SL-1210 - oh nice one would you be able to send it over please?

And ok I guess I have a lot to learn. Can anyone recommend some books or best ways of learning what I set out to achieve?

 

[sean_ork]

Sign of the times - start a "business" then learn how to do it via YouTube.

service - https://www.technologicturntableservicing.com/service/

 

[Lucien Nunes]

would you be able to send it over please?

Er, no, I'm not going to pay for it or infringe the copyright. You can do those yourself.

BTW, you're not in the business of wind-up gramophones are you?

 

[Jonathan Wilcox]

Er, no, I'm not going to pay for it or infringe the copyright. You can do those yourself.

BTW, you're not in the business of wind-up gramophones are you?

Sorry, Lucien. I didn't realise. I'm not sorry but here is a guy The Gramophone Guru – Expert repairer of wind-up gramophones and phonographs - http://gramophoneguru.com/

Sign of the times - start a "business" then learn how to do it via YouTube.

service - https://www.technologicturntableservicing.com/service/

OK thanks Sean, could I ask why the link to my page? thnx

 

[DPG]

I think things have been covered pretty well by Lucien. If you are embarking on providing electronic repairs to component level then you have some reading and learning to do.

A college course would also be useful, although the number of colleges offering the old C&G electronic repair courses will be pretty much nil now I imagine. ONC electronics would be a good course to consider.

To add to Sparkychick's comment about capacitors - for testing electrolytic capacitors then I would recommend an ESR meter. Rather than measure the capacitance value (which if taken alone can be misleading), these give a reading of the capacitors effective internal impedance - this is a type of 'goodness' factor of the component. Electrolytic caps are probably the component most affected by age, etc. due to how they are made.

 

[sean_ork]

OK thanks Sean, could I ask why the link to my page? thnx

Your website says your day job is "digital marketer" - but you've had to ask why I've posted a link to your website.

You appear to be running a business of some sort offering test and repair services on an electronic item.

Your site states "check fuse, voltage regulator, diode components"

Yet you are asking electricians for advice on testing the most basic of components, including one which according to your site you allready test.

Something is amiss.