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Old 30th Apr 2019, 7:54 pm   #1
Radio Surfer
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Location: Tiree, Argyll & Bute, Scotland, UK.
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Default Hacker RP37A Inter Station Muting Issue

Hello,

Here's my first query on the forum after joining a few weeks ago. Hopefully, someone may have seen this before and have some advice.

I've finished renovating a Hacker RP37A and have been really pleased with the results with only a few cosmetic jobs to complete. The radio has been working really well and I can listen to FM radio once more. I posted a note in the new membership forum on why I ended up buying a Hacker and the frustrations of DAB radio and the internet options.

Anyway, all has been working well apart from a problem for which I now see the cause but not the solution. It seems that as the batteries run down, the inter station muting (with button depressed) cuts the radio off and requires the internal thumbwheel preset for the I-SM sensitivity to be adjusted (typcally adjusting weekly). The adjustment is very sensitive with what seem to be dead spots. I've tried cleaning with normal electrical contact cleaner, but that's not made any difference. Having just put some new batteries in, I've had to adjust again. The adjustment wheel has a paint mark in light green which shows the ideal "sweet spot" with fully charged batteries, presumably marked during initial manufacture set up?

The old batteries show a combined voltage of 16v, compared with the new just over 18v.

Any thoughts on what the issue might be?

Regards, Richard

PS, the radio has just turned off as I type this, after about 2 hours with the new batteries so maybe not linked to the batteries running down. A quick tweak of the preset and all is fine again.
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Old 1st May 2019, 8:09 am   #2
Nuvistor
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Default Re: Hacker RP37A Inter Station Muting Issue

16v should work the radio correctly, you say the control has dead spots, perhaps it is just a faulty control.

Is the battery life poor, check the current drawn from the batteries is it in line with the service manual?
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Old 1st May 2019, 9:46 pm   #3
Radio Surfer
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Default Re: Hacker RP37A Inter Station Muting Issue

Hello Frank,

I gave the preset another clean with Servisol. Ideally I'd like to remove the plastic wheel, but couldn't see an easy way of doing this. Now at least the dead spots are gone and it turns smoothly. I adjusted the preset to the point hissing just drops out and all was fine for about 2 hours before silence resumed. With the ISM button out the radio is now quiet and muffled, something new.

I've downloaded a service manual for an equivalent Hacker with the same FM set up (was there never one for the 37A?) and will go through some tests when work allows. Looks like it might be a bit more involved than I first thought.

Anyone with some bright ideas, please pass them on.

Regards, Richard
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Old 2nd May 2019, 6:59 pm   #4
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Default Re: Hacker RP37A Inter Station Muting Issue

Differences between the 37 and 37A.

The voltage on the batteries should not drop from 18v to 16v with just 2 hours use, if that is occurring it needs investigation.
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Old 3rd May 2019, 10:46 am   #5
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Default Re: Hacker RP37A Inter Station Muting Issue

Hello Frank,

Thank you for the documents, more bed time reading.

Just to clarify, the drop in voltage was over a 3 week period using radio on average 10 hours a day during which it was fine. Since replacing the batteries, it has more recently deterioted, lasting a couple of hours before ISM fails and needs resetting, to a few minutes. Now I can only get a distorted signal with the ISM button out, so what was an intermittent problem has progressed to something more permanent. On the positive side, that should be easier to identify. With intermittent issues you can never be sure you've fixed it and be led down the wrong path.

Once I've read the notes I have and more importantly got some free time (work and decorating still to do!) I'll start testing and narrowing down possible areas. I'm now thinking it's nothing to do with the thumbwheel and probably a capacitor/transistor breaking down.

Hopefully, I'll be back with a success story soon(ish).

As always, any suggestions welcome.

Regards, Richard
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