[volt-nuts] volt-nuts Digest, Vol 95, Issue 18

Sat Jul 22 13:14:33 EDT 2017

Verzonden vanaf Samsung-tablet.

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Van: volt-nuts-request at febo.com 
Datum: 22-07-2017  18:00  (GMT+01:00) 
Aan: volt-nuts at febo.com 
Onderwerp: volt-nuts Digest, Vol 95, Issue 18 

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Today's Topics:

   1. Re: Datron 4700 manual and options (Fred)

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Message: 1
Date: Sat, 22 Jul 2017 09:27:16 +0200
From: Fred <pa4tim at gmail.com>
To: volt-nuts at febo.com
Subject: Re: [volt-nuts] Datron 4700 manual and options
Message-ID: <61b14813-7e68-278e-7d40-7ae4c88b1318 at gmail.com>
Content-Type: text/plain; charset=utf-8; format=flowed

The 4700 is fixed. The 400V issue was caused by missing -15V, That was 
caused by a shorted tantalum on the Ohms board. It was less then 0,1 ohm 
but not even discolored.

I was curious about the way they die. So a desoldered about 20 tantalums 
and measured C, D and leakage current. New ones have a very low D, at 1 
kHz well under 0,1. Capacitance did not decrease much like electrolytics 
do, but D does increase over age. Leakage current is as good as zero, 
(my best leakage tester has only 1 uA resolution so it can not measure 
leakage in the nA's)

The worst D i found was 0.67.
They did not leak, so I think they go from good to short in one step.
capacitance does not seem to decrease. In electrolytics this is caused 
by a decreasing oxidelayer caused by the decreasing electrolyte.

I replaced a few by electrolytics as a test. The D factor of the 10uF  
low ESR panasonic FM caps was better as that of the new 10uF tantalums I 
had. Most tantalums measured OK, a few had very high D, non of them 
leaked DC.

So I think (based on this to small number test) they get a high D, start 
to dissipate and as a result of that develop a short.

Fred

On 07/21/2017 01:59 AM, Todd Micallef wrote:
> Fred,
>
> I used the same values and typically went up to the next higher voltage. I
> think most ended up as 35v since I bought them in quantity. Some people
> recommend the OS-CON family as replacements. Many of the failed tantalums
> fit in a tight space so I just stayed with the original type.
> Once the in-guard was repaired, I found a few other boards where the
> tantalums on the same rail also failed so don't be surprised if more start
> to fail.
>
> The 4708 service manual is here
> https://xdevs.com/doc/Datron/4708/DATRON-4708-CH-SH_c20030307.pdf
> It is now uploaded to KO4BB. The 4808 service manual will be very close
> since the 4708 and 4808 share similar designs.
>
> The 4708 uses a LTZ1000 as the reference instead of the array of zeners
> used in the 4000 and the lower spec'd 4700. You will have yourself a good
> calibrator once it is brought back into service. Be careful around the
> displays as there is hardly any room between the glass and front panel.
>
> Respectfully,
>
> Todd
>
> On Thu, Jul 20, 2017 at 12:55 PM, Fred <pa4tim at gmail.com> wrote:
>
>> Hi Tod,
>>
>> I just pulled that board (i think) and found a burned 22uF tantalum.
>> Tantalum caps should have a very long life unless used on the wrong place.
>> I guess this is an example. I do not even stock them, the last bad one I
>> had to replace was in a G&M secutest 2 years ago. ( I repair around 10-20
>> Secutests a year and that was the only bad tantalum)
>>
>> With what type/value cap did you replace them ?
>> I found the 4708 manual at KO4BB but that is a user manual without
>> schematics.
>>
>> The calibrator should be OK but before I try to start her I always like
>> check things like caps, connectors, solderjoints etc. It really looks like
>> new, not even a scratch or dust. It came with a new looking HP8640 and a
>> new looking HP counter 5248. Both from the same cal lab (part of a company
>> that stayed there) that cal-lab closed about 30 years ago, but all gear
>> stayed where it was (I already had received most of their gear a few years
>> ago). This were the last things because my friend retires.
>>
>> Fred
>>
>> .
>>
>> On 07/20/2017 04:51 PM, Todd Micallef wrote:
>>
>>> Fred,
>>>
>>> Shorted tantalums most likely. I had several on mine that went bad as
>>> quickly as I replaced them. I would start with the inguard supply board.
>>>
>>> I think the 4708 manual is available for download at KO4BB or xDevs. If
>>> not, I can dig up something. I have a set of the manuals.
>>>
>>> Todd
>>>
>>> On Thu, Jul 20, 2017 at 10:01 Fred <pa4tim at gmail.com> wrote:
>>>
>>> Today a friend gave me a Datron 4700. It looks like new. It is stored
>>>> (working)  for many years in the cal lab he works. He was allowed to
>>>> take it home (for me, in return I will repair his SA), He plugged it in,
>>>> Fail 1 on the display followed by a sound and a smell.
>>>> I opened it but nothing looks burned.
>>>>
>>>> I can not find a service manual, does someone has one ?
>>>>
>>>> On the back the label shows no options but if he remembers it well it
>>>> should have all or at least most  options. All slots are filled with
>>>> pcb's. The "box" in the left upper corner is full and there is a very
>>>> small pcb next to it. There is not much room left. Just enough to store
>>>> a small multimeter between the huge transformer and that box.
>>>>
>>>> Fred
>>>> www.pa4tim.nl
>>>>
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