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Old 28th Jul 2018, 1:09 am   #33
Argus25
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Join Date: Oct 2016
Location: Maroochydore, Queensland, Australia.
Posts: 2,679
Default Re: Hacker Sovereign 11

One of the things that characterizes a good repair, from a poor one, it is a "targeted repair" based on measurements and deductions. The worst thing a technician can do is to start replacing parts with a "stab in the dark" approach. The reasons for this are multiple and more complex than you might first think:

1) More pcb damage is done. Remember in these old radios the adherence of the foil to the phenolic board is much more fragile and heat sensitive than a modern pcb and there are no plated through holes which give extra support to component pads. So care and temperature controlled de-soldering & soldering is required to preserve the pcb.

2) New faults can be introduced if there are issues with the substituted parts.

The above can lead to a cyclical degradation of the board being repaired.

3) But, here is the worst of it:

Human psychology explains that this blind approach to servicing electronic equipment is rewarded and sustained by the phenomenon of intermittent reinforcement. For example if this cut & try approach works only 1 in 7 times, that reinforces the technician's bad behavior and it is very difficult to extinguish it, even with a run of multiple losses or failures. (this is why rewards in gambling, for example the Pokies or scratch tickets, give a reward at a rate of about 1/7, so the gambling is reinforced) This was all worked out many years ago with an enclosure called a Skinner Box, with a rat being rewarded with a grain of rice for pushing on a metal bar and various reinforcement schedules were tried. If the rat is rewarded for pushing on the bar at a rate of about 1 in 7, and then if the reward is withdrawn, the rat keeps trying for the longest number of attempts before it gives up. Turns out it is about the same rate for humans.(I certainly don't mind being compared to a rat myself, they are spectacularly intelligent animals for their size and I'm very fond of them)

Therefore, the best move is to take multiple measurements on the faulty pcb before concluding & doing anything.

As noted in my previous post the minimum equipment is a multimeter +/- a crystal earphone.

So do what you are doing, take your time, think about it, read about these amplifier circuits, make measurements (especially the 1/2 rail voltage) and collect some data. Then with that data the forum members can also help guide you to the fault and it can be a "targeted repair".
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