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Old 15th May 2019, 12:06 pm   #1
Tully Bascombe
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Default Dynatron Jewel TP30 - first attempt at repair/restoration

Got myself this Dynatron Jewel at a reasonable price for my first newbie attempt at restoration. At first I thought it was dead but after much head scratching it suddenly sprang to life, albeit with low volume and a hint of distortion.

I'm sure the culprits are the electrolytic caps in the amp section which have odd values such as 350uF and 8uF. I guess it's OK to replace these with the nearest equivalents, 330uF and 10uF? And does voltage rating matter as long as it's more than the 18V operating voltage of the radio?

Cheers,
Tully
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Old 15th May 2019, 12:38 pm   #2
Herald1360
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Default Re: Dynatron Jewel TP30 - first attempt at repair/restoration

Your e-cap strategy is fine. You might have problems with the AF11x transistors, they are now notorious for tin whisker problems. There are many possible replacements but two possible direct electrical though not pinout subs are the AF12x series and the Russian GT322b types. Lots of posts here on the topic!

https://www.service-data.com/product...25/1893/a11325

May be helpful if you haven't already got service data.
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Old 15th May 2019, 1:04 pm   #3
Tully Bascombe
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Default Re: Dynatron Jewel TP30 - first attempt at repair/restoration

Luckily this radio does not appear to suffer from the notorious AF11X whisker problem, yet! It's pulling in well on both MW and LW albeit at lowish volume.

If I can avoid replacing those pesky transistors, so much the better.
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Old 21st May 2019, 10:06 am   #4
Tully Bascombe
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Default Re: Dynatron Jewel TP30 - first attempt at repair/restoration

Some progress on the Jewel. I've pulled all the electrolytics from the PCB and tested their state of health.

Here are the results according to the LCR-T4 component tester:
CCL 350uF 9V(?) - open, dead
CCL 2uF 50V - 6.9uF ESR 9 ohms, Vloss 11%
CCL 8uF 50V - 9.3uF ESR 0.14K ohms, Vloss 20%
CCL 8uF 50V - 14uF ESR 1.8 ohms, Vloss 2.3 %
Plessey 100uF 6V - open, dead
Plessey 100uF 12V - 113uF ESR 7.2 ohms, Vloss 5%

Dynatron did not make this servicing job easy as all the component leads have been bent over on the copper track.

Next job is replacing all 6 caps and hopefully the low audio output will be fixed.
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Old 21st May 2019, 12:07 pm   #5
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Default Re: Dynatron Jewel TP30 - first attempt at repair/restoration

It was standard practice on early PCBs to bend the component legs over before soldering. It would hold the components in place until they were soldered, either by hand or solder wave machine. Later you may find the leads have a sort of crimp spread instead done by a powered lead trimmer tool.


Modern SMD boards use a hot melt glue spot when the parts are placed. When the board goes through the oven, the glue softens and the surface tension of the solder together with the cunning layout of the solder pads pulls all the connections and the chip into perfect alignment.
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Old 21st May 2019, 12:15 pm   #6
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Default Re: Dynatron Jewel TP30 - first attempt at repair/restoration

Capacitors should be replaced, as the OP says, with the nearest modern 'preferred' value -i.e. 330uf for 350uf 10uf for 8uf, etc. The working voltage should be equal to, or greater than, that of the original component.
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Old 22nd May 2019, 2:56 pm   #7
Tully Bascombe
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Default Re: Dynatron Jewel TP30 - first attempt at repair/restoration

I have now completed the re-cap which has improved the volume level but not as much as I was expecting for an 18V set of this type. Max volume gives a comfortable listening level on a strong station but it's certainly not loud.

Difficult to know if this is normal for this model or if there's something else wrong. Troubleshooting isn't easy as no voltages are given on the circuit diagram.

Sensitivity is good so the RF section appears to be healthy.
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Old 22nd May 2019, 9:12 pm   #8
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Default Re: Dynatron Jewel TP30 - first attempt at repair/restoration

Possibly (probably) one of the IF transistors have the whisker problem or the overload diode D1 or detector faulty. Although voltages are not shown you can always use a similar radio circuit with voltages to get an good idea if the voltages are way out.
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