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Old 8th Mar 2017, 11:47 pm   #41
indigo.girl
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Default Re: Dynatron SRX30D: LH quieter than RH output

Quote:
Originally Posted by gezza123 View Post
here is your circuit.
Thanks Gezza - you are a life saver!

I've now been able to check out the spec voltages on the pre-amp circuits (500 series components) and all voltages check out OK.

When I bypass the pre-amps and input a signal at C301 (the cap that connects to pin 2 of the MC483 chip on LHS) I still get a much weaker output compared to the same position on the RHS. So I can rule out a fault with the preamp.

I'm wondering if my problem could be with the balance slider. To do these tests on LHS or RHS only I have to move the slider all the way up or down. If the slider itself was faulty I may think I am at max LHS but this may not be the case. Is there anyway I can test the slider?

Also, I'm not familiar with this MC483 chip and so I'm not sure where I should do any signal injecting in this bit of the circuit. Any ideas were to inject next?
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Old 8th Mar 2017, 11:56 pm   #42
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Default Re: Dynatron SRX30D: LH quieter than RH output

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Originally Posted by Hetrodyne View Post
If the fault is common to radio on AM FM and the gram and the fault is transferred to the other main amplifier if the input plugs to the main amplifiers are swapped do the two channels sound different even with the mono/stereo switch set in mono? Have the input capacitors to the tone circuit been check, and the switches/plugs and sockets around this part for poor solder joints. I see the input capacitors to the tone circuit have been changed with no improvement.
Good test idea - thanks Heterodyne. When I switch from STEREO-MONO I still get the same problem with LHS audio very weak. The mono-stereo switch is after the pre-amp and just before the tone control section so this also suggests that the problem must be in the tone control section.
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Old 9th Mar 2017, 10:02 am   #43
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Default Re: Dynatron SRX30D: LH quieter than RH output

If I've read all this right you've established that the fault lies before the main amplifier, if that's the case then there's two ways to approach this, one way would be to start around the preamp boards output circuitry with signal injection and work back to the preamps input, the other way would be to try and eliminate the unobtainium part (MC483) out of the equation first.

Time difference wise there's not a lot in it so I would set the volume control to full, the balance control to midway and the contour switch to on and inject a signal at the top end of the volume control (as viewed in the schematic) and compare both channels as a starting point and take it from there.

Lawrence.
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Old 9th Mar 2017, 10:58 am   #44
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Default Re: Dynatron SRX30D: LH quieter than RH output

That's the way I understand it Lawrence, agree with the signal injection.
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Old 9th Mar 2017, 11:11 am   #45
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Default Re: Dynatron SRX30D: LH quieter than RH output

Might be worth checking the output plug/socket to the main amp on the left channel as it is the only other part in the signal chain that doesn't swap places when swapping main channels. A poor 'earth' return because of a faulty pin in the output socket or a poor solder joint could cause this fault.
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Old 9th Mar 2017, 11:39 am   #46
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Default Re: Dynatron SRX30D: LH quieter than RH output

I remember these you need to swap over the MC483's to confirm this is at fault as has been said they were unobtainable years ago!
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Old 9th Mar 2017, 12:08 pm   #47
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Default Re: Dynatron SRX30D: LH quieter than RH output

Are there two separate chips, I thought both channels where in one chip, if two and they are in sockets then this would be the first thing to try. Even if just one chip it might be worth carefully easing it out of the socket as the pins can get a bit tired or corroded and need a clean.
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Old 9th Mar 2017, 2:53 pm   #48
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Default Re: Dynatron SRX30D: LH quieter than RH output

I've located the problem!! I've been signal injecting step by step along the circuit and found a problem around the coupling capacitor C313. This had been replaced (post #28 but had not solved the problem at the time) however resoldering around the area has now solved the problem.

Thanks for your help everyone - has been a great learning exercise for me. Must get my signal injector out first before swapping caps I think next time!
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Old 9th Mar 2017, 3:01 pm   #49
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Default Re: Dynatron SRX30D: LH quieter than RH output

Good result then

Measurements, signal injection/tracing plus a bit of circuit theory is the only way to become a good troubleshooter for sure.

Wot's next?

Lawrence.
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Old 9th Mar 2017, 3:01 pm   #50
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Default Re: Dynatron SRX30D: LH quieter than RH output

For anyone following this is the future:

The circuit diagram in this manual appears to be the one for SRX29A and is slightly different to the one for SRX30D. The SXR29s have a different preamp stage (the 500 series components) to the SRX30. Here are the board layouts for SXR29 vs SXR30:

SRX29:

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SRX30:

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In the circuit diagram there are 4 transistors labelled TR501, 502, 503, 504.
However, on the SRX30 layout TR502 is called TR506. The rest are the same.
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Old 9th Mar 2017, 3:07 pm   #51
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Default Re: Dynatron SRX30D: LH quieter than RH output

Quote:
Originally Posted by ms660 View Post
Wot's next?
Putting the damn thing back together and figuring out the tape mechanism... it ain't over yet
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Old 9th Mar 2017, 3:11 pm   #52
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Default Re: Dynatron SRX30D: LH quieter than RH output

Good luck...!

Lawrence.
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Old 9th Mar 2017, 3:11 pm   #53
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Default Re: Dynatron SRX30D: LH quieter than RH output

For future troubleshooters here are a few more pages from the manual showing layout.
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Old 9th Mar 2017, 3:23 pm   #54
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Default Re: Dynatron SRX30D: LH quieter than RH output

I never liked working on any cassette mechanism. The electronics ok, but not the mechanics.
Have fun.
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Old 9th Mar 2017, 4:33 pm   #55
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Default Re: Dynatron SRX30D: LH quieter than RH output

Well done,Indigo-girl

I will put that TR506/502 IN THE BOOK
should look something like this when you have finished.

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Old 9th Mar 2017, 5:04 pm   #56
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Default Re: Dynatron SRX30D: LH quieter than RH output

The Cassette Deck unit electronics/mechanics on your Dynatron was also sold as a stand-alone Stereo Unit unit by Philips and Pye. I had one with DNL noise reduction and I must say it really did sound very good on Chrome Tapes. The features/benefits of DNL against Dolby is worth another thread of its own.....
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Old 11th Mar 2017, 5:30 pm   #57
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Default Re: Dynatron SRX30D: LH quieter than RH output

I SPOKE TO SOON!! My fault is back!

I have disassembled again and redone the signal injection and the problem is the MC483 chip. Yesterday resoldering the capacitor that is connected to pin7 solved the problem and the LH channel had definitely kicked back in. All I can think it that the heat transfered to the chip and freed something up that has now returned to faulty....

All that's left to do I think is to remove both chips and swap them round to confirm its the chip at fault.... but I guess if MC483 is not available any more there's nothing I do to get this one back up and running :-(
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Old 11th Mar 2017, 5:45 pm   #58
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Default Re: Dynatron SRX30D: LH quieter than RH output

It's the spawn of the devil...fingers crossed.

Lawrence.
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Old 11th Mar 2017, 6:59 pm   #59
indigo.girl
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Default Re: Dynatron SRX30D: LH quieter than RH output

Well I almost can't believe this but I've just melted the solder briefly on each of the pins of the faulty MC483 and its cured the fault again. Left it for 30mins and the fault is back. What on earth is going on??
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Old 11th Mar 2017, 7:09 pm   #60
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Default Re: Dynatron SRX30D: LH quieter than RH output

Expansion and contraction making and breaking a connection inside would be the usual explanation.

Lawrence.
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