Juno-106 Restoration story/Power Supply woes

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Re: Juno-106 Restoration story/Power Supply woes

Postby Mooger5 » Sun Jan 13, 2019 1:15 pm

Thanks for the link. That meter seems well built but it only reads ESR.

I´m buying and recommending the other one because it reads lots of other stuff.
Why do you say it can´t read ESR in circuit? I see a cap attached to the ZIF socket. I think it´s possible to attach test leads instead and use them to test the caps directly on PCBs...

I built one years ago and still use it. The principle is very simple. It consists of a square wave oscillator running at a fixed high frequency. Then it goes a through a passive lowpass filter (or some diodes, can´t remember) to fake a sinewave. The osc output then goes through a small mains 220/12 transformer used for stepping the signal down to a very faint level. (If the cheap ebay meter outputs a test signal as low as this, it will be capable of reading in circuit).
Then the return signal is read by a microamp meterand that´s it.
Caps are reactive. The higher the frequency the more they will appear as a short circuit to AC. You can regard DC as just an infinitely low frequency AC. The rest is simple: to calibrate the uA meter we short circuit the test probes and move the needle to maximum Amperage. This equates to zero Ohms, or the lowest ESR possible. Then we use a 1 ohm resistor, and the needle should move bit to the left, then a 2 ohm resistor and the needle moves another bit, and so on. Simple and effective. Of course the uA scale is now an ESR scale and must be redrawn, but I´m not very good with graphics. I just use it intuitively and just KNOW when a cap is good or not by looking at the scale.

I can post some pictures of it later.
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Re: Juno-106 Restoration story/Power Supply woes

Postby Yekuku » Mon Jan 14, 2019 11:23 am

Goodmorning Mooger5 and thanks for the explanation it was very informative .
I got one a similar to this one :
Image
While it is a very helpful tool, due to its automatic nature, it can not be forced manually into reading ESR or test a specific component type.
What I mean is when you use it in circuit, the surrounding components affect the test results and most of the times it does not recognize the capacitor under test or misidentifies it as another component, so it does not display its ESR.
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Re: Juno-106 Restoration story/Power Supply woes

Postby Mooger5 » Mon Jan 14, 2019 2:12 pm

I see. Theye fully automatic. Thought you could tell the meter whst tests to run. But it instrad scans the zif terminals to guess the component type.
The voltage used by a incircuit esr mtr has to be lo enougj to prevent it from triggering adjacent components to the cap under teston the pcb.
Since the auto tester is designed to detect semiconductors as well, it does exactly the opposite.

Anyway it can be useful for tezting salvaged caps or those that have been in storage for a long time...
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Re: Juno-106 Restoration story/Power Supply woes

Postby Mooger5 » Mon Jan 14, 2019 2:22 pm

Btw that meter you linked to is not as expensive as some I have seen.
The gadget I built is mostly from salvaged parts but still had to pay for the ampmeter, the project box and the probes.
Add to that a few hours of work and the usual hassle and that ready made tester now looks a worthy investment.

Cheers
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Re: Juno-106 Restoration story/Power Supply woes

Postby Yekuku » Mon Jan 14, 2019 3:09 pm

Unfortunately there is no way of testing components manually. :(
I got mine for $7 , 3 years ago and it upgraded my workflow.
Just like you said, I made an adapter with 3 probes ( parrot clips) and I am using it to test components in circuit , especially transistors. I had some problems with power MOSFETS which were not identified, but this was due to the unit not having enough power to turn them on.
It is great for quickly testing salvaged parts, although big capacitors need a few more seconds to get a reading.
Best $7 ever spent !
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Re: Juno-106 Restoration story/Power Supply woes

Postby The LT » Fri Jan 18, 2019 1:09 pm

Ordered the last batch of replacement parts. 80012As, 5534s, bender faders, foil caps, etc. Once they get here from the US this will hopefully result in both units singing. :)
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Re: Juno-106 Restoration story/Power Supply woes

Postby Yekuku » Fri Jan 18, 2019 11:46 pm

Good luck LT, let us know how it goes ! :ugeek:
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