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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 7th Sep 2006, 9:20 pm   #41
Superhet Si
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Default Re: Are AF11*'s repairable?

You could try araldite as this sets quickly and with little heat generation.
It also conducts heat fairly well and the junctions of the transistor will push through the low viscosity of the freshly mixed glue. Yummy!!
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Old 17th Oct 2006, 8:19 pm   #42
Kat Manton
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Default Re: Are AF11*'s repairable?

Hi,

My dead AF11x collection seems to have increased with the addition of Hackers RP30, RP35 and yet another RP18 to the collection, none doing anything other than going "plop" at switch-on.

Watch this space for results of a bulk AF11x resurrection session, coming soon...

Regards, Kat
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Old 21st Oct 2006, 9:04 am   #43
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Default Re: Are AF11*'s repairable?

Hi,

I've just been reading a new item on the NASA Goddard Space Flight Center Tin Whisker (and Other Metal Whisker) Homepage, specifically "Evaluation of Conformal Coatings as a Tin Whisker Mitigation Strategy, Part 2".

It seems the whiskers managed to penetrate the various coatings tested.

Fascinating stuff. But, going by that research, it looks like coating the inside of our transistor cans will merely slow whisker growth down a bit.

Regards, Kat
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Old 21st Oct 2006, 1:28 pm   #44
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Default Re: Are AF11*'s repairable?

Hi again,

I've made a start.

The victi... research subject in question: One red Hacker RP30 Herald, serial 67656. Found to have an oscillator which didn't, cause... you guessed.

I decided to take the transistor apart, but it proved somewhat recalcitrant. I'd definitely got it hot enough to melt the solder, only the 'lid' seemed to be on tight. Eventually I gave up, thinking I'd probably destroyed it anyway.

Once it'd cooled off, just out of curiosity I checked it anyway. My meter claimed there was still a couple of diode junctions inside and there was no leakage from anything to the screen lead. So I tacked it temporarily on the back of the board and... one working Herald. I've since fitted it properly and I'm sat listening to it as I type this.

So, heating the case up melts the whiskers; not exactly unexpected. I'll make a note of what I've done and when and pop it inside the radio. Let's see how long this lasts...

Regards, Kat.
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Old 8th Nov 2006, 12:02 am   #45
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Default Re: Are AF11*'s repairable?

Tried this with the transistor in circuit just placed the soldering iron on the top of the can, waited till the solder on the rim was melted and cooled with a damp cloth...can't get much simpler than this..Peter
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Old 8th Nov 2006, 8:51 am   #46
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Default Re: Are AF11*'s repairable?

Quote:
I decided to take the transistor apart, but it proved somewhat recalcitrant. I'd definitely got it hot enough to melt the solder, only the 'lid' seemed to be on tight. Eventually I gave up
I have also noticed this, the very first Hacker that I restored (an RP18)also had transistors that I simply could not get apart. I even tried with a mini gas blowtorch .

However like Kat, I thought I may as well test them before binning, and was shocked to find they actually worked.
Even after 2 years, the set still performs wonderfully.

I have another RP18 that I am restoring for a friend, so I will try this first before struggling to remove the transistors.
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Old 8th Nov 2006, 9:34 am   #47
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Default Re: Are AF11*'s repairable?

This idea casts a very different light on the viability and therefore the chances of survival of more than a dozen sets in my little collection alone.

I have now tried the soldering iron on the can technique with no fewer than eight AF11*s and have achieved the desired result in every case! Remind me, what was all that heatsink, in & out in a second, don't let Ge devices get hot, all about?!

I can only wait and see how long-term reliability pans out, but at this rate, I'll be able to turn my pile of AF127s and 125s into spending money for Christmas!
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Old 8th Nov 2006, 6:36 pm   #48
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Default Re: Are AF11*'s repairable?

My guess is there are a couple of reasons why this works:
1. the heat is applied to the can which is insulated from the Ge and is only applied for a short time and cooled down quickly.
2. there is a big blob of silicon grease over the Ge with a high thermal capacity which prevents the Ge temperature rsing too quickly.

Even so I turned on a radio immediately after cooloing and it was dead presumably from chronic leakage but gradually recovered as it internally cooled.
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Old 9th Nov 2006, 5:36 pm   #49
G0PKH - Pete
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Default Re: Are AF11*'s repairable?

Well,

The Hacker Sovereign RP18 I was repairing for a friend now works, all 4 AF114's responded well to the treatment. Once I had replaced the diodes in the ratio detector, it sounded even better, one had gone leaky, and I couldn't balance it.

This technique certainly seems to work, for how long we can't be sure.
Even better was the fact that I performed the act with the transistors in circuit. They are a to remove in the RP18.

Pete
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