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 Post subject: Bridge rectifier RE A 65br9
PostPosted: Mar Wed 07, 2018 2:53 am 
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I have an RCA 65 BR9 portable radio that gets no voltage to its on board battery, and all signs point to it having a dead rectifier. Coming out of the power transformer I get 4 volts ac which seems right to me considering this set works off of a 2 volt battery. Coming out of the bridge rectifier assembly, I get nothing ac or dc. Schematically speaking i can't see anything else between the transformer and the rectifier, so would my diagnosis of a bad rectifier be correct?


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 Post subject: Re: Bridge rectifier RE A 65br9
PostPosted: Mar Wed 07, 2018 5:00 am 
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Location: Oxford, MI
Here's the schematic: http://www.nostalgiaair.org/pagesbymode ... 015060.pdf

It looks like part of S1 also controls the charging of the battery after the rectifier, and L10, a filter choke is in series with the lead going to the negative side of the battery. Both of these could be suspect.

I believe that the rectifier employed is of the copper oxide type and there is a way to repair them if they have issues. the first thing to try is tightening the mounting bolt as they sometimes just loose contact, but in more advanced cases the oxide layer can be reformed. IIRC, the procedure involves impressing a high voltage across the terminals.

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 Post subject: Re: Bridge rectifier RE A 65br9
PostPosted: Mar Wed 07, 2018 6:27 am 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: North of Mpls, Minnesota
The method of reviving a copper oxide rectifier is to short the output for about 30 seconds.

Dave


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 Post subject: Re: Bridge rectifier RE A 65br9
PostPosted: Mar Wed 07, 2018 7:20 am 
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Joined: Dec Sun 13, 2015 2:17 am
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Good to know, thanks. If I was to replace the original rectifier with modern diodes, what would the current demand be?


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 Post subject: Re: Bridge rectifier RE A 65br9
PostPosted: Mar Wed 07, 2018 8:56 am 
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Dave is correct about the rectifier, I had to recheck my notes. The idea is that the oxide layer will reform after the rectifier discs are heated by shorting the output and then cool down.

Current output for the charger will vary depending on the charge state of the battery but will likely range from between 1.5-2.0 amps. If a silicon bridge rectifier is used the issue would be that copper oxide rectifiers have a forward voltage drop that is less than that of silicon.

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 Post subject: Re: Bridge rectifier RE A 65br9
PostPosted: Mar Wed 07, 2018 9:05 am 
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Location: North of Mpls, Minnesota
There hasn't been a good replacement for copper oxide rectifiers until recently. They now have Schottky which are very close. I would try 15SQ045 which is a 15 amp 45 volt Schottky.

Dave


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 Post subject: Re: Bridge rectifier RE A 65br9
PostPosted: Mar Thu 08, 2018 6:32 am 
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Joined: Dec Sun 13, 2015 2:17 am
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I found some 1n5392 diodes in a box of junk that tested good. Would they be up to the task?


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 Post subject: Re: Bridge rectifier RE A 65br9
PostPosted: Mar Thu 08, 2018 7:25 am 
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Location: Oxford, MI
1N5392 datasheet is here: https://www.vishay.com/docs/88514/1n5391.pdf

It looks like the current capability is a bit undersized for this application and the forward voltage drop is 1.4V which will reduce your charging voltage quite a bit. I would not recommend it.

The Schottky diode that Dave is referring to seems to be a good fit. It looks to be available from most vendors for about a buck a piece. Four would be required for a bridge.

However, has the rectifier been determined to be at fault? It may not be the sole culprit for why the battery is not charging.

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 Post subject: Re: Bridge rectifier RE A 65br9
PostPosted: Mar Thu 08, 2018 8:17 am 
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Joined: Dec Sun 13, 2015 2:17 am
Posts: 124
Ok thanks. I got the suggested diodes coming. The rectifier was indeed the fault. I tried shorting it and at one time was getting almost a volt of Dc through. at times I would also get the same amount of ac that the secondary of the power transformer was making which tells me that the unit is shorted. I took it out of the circuit and the fluke meter revealed it to be shorted. I checked it with a diode checker, and it failed that as well.


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 Post subject: Re: Bridge rectifier RE A 65br9
PostPosted: Mar Thu 08, 2018 9:28 am 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: North of Mpls, Minnesota
I just ordered some of these and will find out how they work after they arrive.
https://www.ebay.com/itm/10pcs-15SQ045- ... 2749.l2649

Dave


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 Post subject: Re: Bridge rectifier RE A 65br9
PostPosted: Mar Thu 08, 2018 8:35 pm 
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Joined: Dec Sun 13, 2015 2:17 am
Posts: 124
Ok. I will do the same with what I ordered. I got mine from Amazon.


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