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Success Stories If you have successfully repaired or restored a piece of equipment, why not write up what you did and post details here. Particularly if it was interesting, unusual or challenging. PLEASE DO NOT POST REQUESTS FOR HELP HERE!

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Old 13th Apr 2018, 11:45 am   #1
vinrads
Octode
 
Join Date: Feb 2009
Location: Chesterfield, Derbyshire, UK.
Posts: 1,615
Default Hacker Hunter RP38A

This radio was a repair I took on from a forum member. As I suspected both the output transistors and let's call it the driver were s/c, the insulation had melted on the outputs, which suggested to me that it had been run on an external power supply.
Having read up on this module I checked all the resistors, most were found to be way out of spec, so I replaced them all including the two pre sets. Also all the transistors were replaced.

With a 0 to 10ma meter in circuit, there is a convenient link for this purpose, a tweak on the pre set gave the 3 m/a quoted in the circuit then set the mid point. This has a direct effect on the idle current, but a bit of re tweaking got it spot on.

When connecting the amp to the radio I was greeted with a howling noise, not motor boating but a constant tone. I tried all the usual suspects like the five pin plug/socket, re soldered all the earth connections, on off switch high resistance, still the same. I found by reducing the 0.1uf capacitor on the input by half the set worked fine. But I needed to find the cause of the problem, tried linking parts of the print on the audio board, no the fault still persisted. Then I linked the earth on the amp board directly to the chassis of the radio, fault cured. In effect bridging the screen on the screened lead, which of course I had checked for continuity before, so I had spent too long on this at that stage. I soldered the link on the five pin plug, and to the radio chassis.

Then I noticed that the slightly noisy amp had gone very quiet. Did the link cure it, don't know, maybe someone who has the same radio would like to try it. Mick.
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