Dynatron SRX25 Radiogram with Garrard 40B, Sound Issue

[Kanyehobbitkind]

Originally Posted by ms660

With the taped transistors still removed from their heatsinks, switch on and try and measure any voltage between the metal of those transistor cases and chassis,

with the attached picture from earlier provided from left to right it goes

The one on the very left won't stop fluctuating but it's in the mV
-31.01

-13.97
-14.18

[ms660]

So...the three you have quoted, is that volts, millivolts?

Lawrence.

[Kanyehobbitkind]

Sorry the other 3 are Volts it's only the first that is Millivolts

Thank you
Kane

[ms660]

Looks like they're leaking, so try the tape trick again that was suggested earlier, when taped and fitted in the heatsinks there should be no voltage reading between the heatsinks and chassis, if there's no voltage readings then the heatsinks can be fitted back on to the pillars.

Lawrence.

[Kanyehobbitkind]

Oh I took them out of the heatsinks first then measured the voltage through the top, did I do that wrong?

Thank you
Kane

[ms660]

You measured them correctly.

Lawrence.

[Kanyehobbitkind]

Originally Posted by ms660

Looks like they're leaking, so try the tape trick again that was suggested earlier, when taped and fitted in the heatsinks there should be no voltage reading between the heatsinks and chassis, if there's no voltage readings then the heatsinks can be fitted back on to the pillars.

I re-taped them, put them in the heatsink then measured the voltage, no voltage readings when they were fitted back onto the pillars.

Thank you
Kane

[ms660]

Just to be clear on all this, the voltage check between the chassis and the heatsinks should be done with the taped transistors fitted to the heatsinks but without the heatsinks being fitted to the pillars or touching anything else, if that results in a measured voltage then the insulation technique has failed, if there's no voltage reading then the insulation technique has worked.

Either way, there would be no voltage reading between the heatsinks and chassis if the heatsinks are fitted to the pillars.

Lawrence.

[Kanyehobbitkind]

Each of them is showing Millivolt readings when the heat-sink isn't connected to the pillar however there is still sound now but I can't fully explain why.

Thank you
Kane

[ms660]

If you were using a digital multimeter then a small voltage reading is possible, if you have the sound ok on both channels then that's good.

Lawrence.

[Kanyehobbitkind]

Awesome!

My only other Issue, I've just got an old record from the shop and put it on the turntable, and the sound on full volume, but it's very very quiet,

I accidentally put pressure on the balance knob and the sound became louder, not as loud as it should be but louder than having to put the speaker to my ear

Is this a totally separate issue?

Thank you
Kane

[ms660]

Sounds like a poor contact somewhere or maybe a pickup cartridge problem.

If you can post a photo of the pickup cartridge someone might recognize it and be able to advise as to its reliability.

Lawrence.

[TonyDuell]

It is possible you have a bad contact in the balance control potentiometer (or in one of the others, such as the volume control) and pressing on the knob improved it. These potentiometers consist of a carbon track (which acts as resistor) with a moving contact (often called the 'wiper') that moves along it, tapping of part of the resistor.

I have just had a similar problem in a Philips N4450 tape recorder where the control potentiometers had bad contacts. As that unit uses rather unusual potentiometers, I carefully took the old ones apart and cleaned the contacts). But if you can get a replacement that is generally a better idea.

[Michael Maurice]

Originally Posted by TonyDuell

It is possible you have a bad contact in the balance control potentiometer (or in one of the others, such as the volume control) and pressing on the knob improved it. These potentiometers consist of a carbon track (which acts as resistor) with a moving contact (often called the 'wiper') that moves along it, tapping of part of the resistor.

I might have agreed with you if the balance pot was like a volume control ie a dual log/antilog pot. But in the Dynatron the bvalance control is a single pot with the slider going to ground (via a capacitor)

It is worth spraying switch cleaner into all the pots and switches to clean them out.

[TonyDuell]

Clutching at straws here, but what if that capacitor was leaky/shorted and pressing the balance control opened the wiper connection?

[Kanyehobbitkind]

Originally Posted by ms660

If you can post a photo of the pickup cartridge someone might recognize it and be able to advise as to its reliability.

Is the pickup cartridge underneath the balance knob?

I figured it out kind of anyway, because underneath the the knob with all the wires a resistor was touching a wire which has a slit in it, which when I pushed down on the resistor stopped the contact between them.
So as far as I can tell it's all working!!

Just need to clean it all up now and make it presentable.

Thank you so much for all your help!
Kane

[Techman]

The pickup cartridge is the bit the stylus fits into on the end of the tone arm. It's probably a Goldring G850 magnetic type.

Good to hear it's all working now.

[Kanyehobbitkind]

Hey again it's only me,

Last night I got the unit home in the boot of my car, got home and the left output isn't working now, I'm honestly starting to think it never was but I'm sure it was,

Any ideas on what it could be?

Sorry to be a pain
Thank you
Kane

[Bookman]

Hi Guys,
I have recently stripped down a few of these units and there would seem to be some good points as well as bad points.
The bad points are the number of plug connectors that are used and the corrosion/oxidisation that is plainly visible on them. I would imagine that they could easily give rise to a fault. This would apply both to the turntable input and the power source.
In terms of the latter there is a transformer located within the unit. It has a 24V (approx) secondary output that feeds a bridge rectifier. There is then a centre tapped output that has a 6.3V a.c output which is probably for the illumination.
Here again the contacts may be an issue and one ought to check them. Indeed, once these have been discounted as possible problem issues the whole system may need a good spray of suitable cleaner/de-oxidiser. Note that there is a fuse located within the amp assembly just behind the power source plug; check that out as well.
I will have a few free output transistors available as spare that I could send you but check out the other issues first. I have also read, on several occasions about units for sale that have had speaker output plug connections by passed?
Regards
Joe

[Kanyehobbitkind]

Hello there,

I've understood about 3% of that haha,
I'm not sure what a centre tapped output is? Or where that or the 6.3v illumination one is? ( all the lights are working efficiently it's literally just the left speaker output that isn't working now)
Thank you
Kane