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 Post subject: Vintage RCA Multimeter Repair
PostPosted: Aug Thu 12, 2021 10:01 pm 
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Joined: Aug Wed 04, 2021 3:43 pm
Posts: 124
Hello,
I'm restoring an RCA WV-536A Taut Band multimeter. There is zero information on the internet about this meter. I've identified 3 burnt resistors and 1 broken Zener diode. 1 of the resistors is burnt with no markings and the Zener has no marking. How is it possible to determine these 2 parts if at all? I've attached 2 photos so you can get an idea of what I'm working on here.

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Thank you for any and all help.
Robb

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 Post subject: Re: Vintage RCA Multimeter Repair
PostPosted: Aug Thu 12, 2021 11:27 pm 
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Joined: Jun Sat 09, 2007 8:14 am
Posts: 5098
Location: Melbourne, Florida
You might want to post a picture of the whole meter. Someone may recognize it but not remember it by model number.

RRM


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 Post subject: Re: Vintage RCA Multimeter Repair
PostPosted: Aug Fri 13, 2021 12:25 am 
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Joined: Aug Wed 04, 2021 3:43 pm
Posts: 124
Good idea. Here are some before removal pics too. Maybe someone will recognize the Zener diode to be replaced.

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Screenshot_20210812-191423_eBay.jpg [ 515.76 KiB | Viewed 1214 times ]
Screenshot_20210812-191423_eBay.jpg
Screenshot_20210812-191423_eBay.jpg [ 515.76 KiB | Viewed 1214 times ]

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Robb
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 Post subject: Re: Vintage RCA Multimeter Repair
PostPosted: Aug Fri 13, 2021 3:05 am 
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Joined: Jun Sat 09, 2007 8:14 am
Posts: 5098
Location: Melbourne, Florida
Before people can help you you need to say what works and what doesn't.

RRM


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 Post subject: Re: Vintage RCA Multimeter Repair
PostPosted: Aug Fri 13, 2021 5:06 am 
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Joined: Aug Wed 04, 2021 3:43 pm
Posts: 124
I've removed the 3 damaged resistors and broken Zener so I don't know the answer to that question. I did put a 1.5v C cell in and check resistance. I was able to get the meter to move on all 3 scales while shorting the test leads. The meter deflected but I couldn't zero it....also the 3 scales were dc 1000 volt position, Rx1 and Rx100 scales. Almost like the rotary switch is not in the correct position.

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 Post subject: Re: Vintage RCA Multimeter Repair
PostPosted: Aug Fri 13, 2021 12:16 pm 
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Joined: Nov Wed 30, 2016 7:35 pm
Posts: 11087
Location: Sunbury, Ohio 43074
With some resistors removed, the meter will undoubtedly think the switch is in the wrong position. Your best bet is to draw out a schematic of the unit. It's the only way we'll be able to help you figure out what to replace the bad parts with.

Are you certain the broken diode is actually a zener, and not just a diode ?

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 Post subject: Re: Vintage RCA Multimeter Repair
PostPosted: Aug Tue 17, 2021 3:33 pm 
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Joined: Aug Wed 04, 2021 3:43 pm
Posts: 124
Your are absolutely correct in that it is a germanium diode. When I test the good one up top with my DMM I get .3v across it and open when the leads are reversed. My question is since this is a multimeter should I choose a higher voltage value for them or a lower voltage value? Say 10v or 100v there is absolutely no visible indication on the remaining diode.

I was able to determine all 3 resistor values. 2 of them had burns but the value was readable and confirmed with a DMM. The 3rd resistor got the scrape and read resistance to the damage then do the opposite direction. I came up with 70 ohms so I went with 75 ohms to add a bit for the damaged area which by the way is clearly visible.

Once I install the resistors the only thing setting me back is the germanium diode. Sorry but I'm not capable of drawing out the schematic. Perhaps someday. Sorry for the delay but I've been under the weather.
Thanks guys.

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 Post subject: Re: Vintage RCA Multimeter Repair
PostPosted: Sep Tue 14, 2021 4:29 pm 
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Joined: Aug Wed 04, 2021 3:43 pm
Posts: 124
The diodes in the meter are SD-46 germanium diodes. They are rated for 50 volts, 30 milliamps. Can these be replaced or at least the missing one...with a higher rated diode? The SD-46 is not readily available. I can get it out of the Russian Federation on eBay if need be. Say 60 volts 50 milliamps? What are the ramifications of doing this?

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 Post subject: Re: Vintage RCA Multimeter Repair
PostPosted: Sep Tue 14, 2021 11:56 pm 
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Joined: Jan Sat 25, 2020 5:23 am
Posts: 700
Location: Colorado Springs, CO 80917
Quote:
2 of them had burns but the value was readable and confirmed with a DMM.

You may be able to return those, then. Some meter resistors are oddball values & getting the exact replacement is impossible or a make-it-yourself project.


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 Post subject: Re: Vintage RCA Multimeter Repair
PostPosted: Sep Wed 15, 2021 12:12 am 
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Joined: Aug Wed 04, 2021 3:43 pm
Posts: 124
hwhall wrote:
Quote:
2 of them had burns but the value was readable and confirmed with a DMM.

You may be able to return those, then. Some meter resistors are oddball values & getting the exact replacement is impossible or a make-it-yourself project.


Actually they are all available. The 2 readable ones looked burnt but were just overheated. Through the grace of the internet I was able to obtain a schematic. The meter was made by Hoiki for RCA. Hoiki is a Japanese company with an office in the USA. I was able to contact tech support who went through Japan and crossed over Hoiki K-228A to RCA WV-536A. Now I'm in business. Hopefully she will be road ready soon and will live her life on my bench.


Attachments:
IMG_1904.PNG
IMG_1904.PNG [ 584.44 KiB | Viewed 368 times ]

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Robb
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 Post subject: Re: Vintage RCA Multimeter Repair
PostPosted: Sep Sat 18, 2021 7:46 pm 
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Joined: Jul Mon 01, 2019 4:42 pm
Posts: 989
Location: St. Louis, MO
hwhall wrote:
Quote:
2 of them had burns but the value was readable and confirmed with a DMM.

You may be able to return those, then. Some meter resistors are oddball values & getting the exact replacement is impossible or a make-it-yourself project.


I've had this problem too. You can always use 2 or more resistors in series to add up to those oddball values though. I remember replacing a bad 900k 1% resistor out of a 680k 1% and a 220k 1% resistor.


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 Post subject: Re: Vintage RCA Multimeter Repair
PostPosted: Sep Sat 18, 2021 8:06 pm 
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Joined: Jun Sat 09, 2007 8:14 am
Posts: 5098
Location: Melbourne, Florida
Robbdoe1 wrote:
.....Through the grace of the internet I was able to obtain a schematic. The meter was made by Hoiki for RCA. Hoiki is a Japanese company with an office in the USA. I was able to contact tech support who went through Japan and crossed over Hoiki K-228A to RCA WV-536A. ... .


You can help others who have this meter by posting the schematic and also by sending it to BAMA.

RRM


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 Post subject: Re: Vintage RCA Multimeter Repair
PostPosted: Sep Sun 19, 2021 5:50 am 
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Joined: Aug Wed 04, 2021 3:43 pm
Posts: 124
Retired Radio Man wrote:
Robbdoe1 wrote:
.....Through the grace of the internet I was able to obtain a schematic. The meter was made by Hoiki for RCA. Hoiki is a Japanese company with an office in the USA. I was able to contact tech support who went through Japan and crossed over Hoiki K-228A to RCA WV-536A. ... .


You can help others who have this meter by posting the schematic and also by sending it to BAMA.

RRM


Yes I will send it to them.

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 Post subject: Re: Vintage RCA Multimeter Repair
PostPosted: Sep Sun 19, 2021 5:53 am 
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Joined: Aug Wed 04, 2021 3:43 pm
Posts: 124
Attachment:
20210919_005236.jpg
20210919_005236.jpg [ 652.81 KiB | Viewed 241 times ]

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Robb


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