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Otrona Attache Power supply 10uF 25v dc working Tantalum Cap Fire

inotarobot

inotarobot

Veteran Member
Joined
Feb 7, 2014
Messages
1,218
Location
Melbourne, Australia
Hi all,

this is going to be an adventure story of Goldilocks, the 3 Bears and their Computer friends.

Once upon a time an older PhD Professor Mr M.W., powered up his Otrona Attache.

Low and behold within moments it started crackling and smoking.

Needless to say he could NOT Bear this to happen so OFF with the Head !! opps sorry wrong story.. OFF With the Power.

He rang me. I arranged to pick it up. I opened it once home.

Yes it had fried one possibly 2 of those orange tag Tantalum's.

The one that was obvious was YOU guessed it , in the most awkward spot under a large metal shielded transformer and behind the fan.

Well I left it for another day.

A lot of Time when by, the bears ate Goldielocks ( because she was elderly .. ) and her Daughter took over anyways and preferred an IPad.

So eventually Prof MW said where is my Otrona as I wish to show it, not an IPad at a computer function in Melbourne this coming September 2026.

So I cleaned of my workbench, and with my new Digital Microscope camera connected to a big +23" LCD Monitor I was able to see way more clearly the damage. ( photos attached).

I had tried previously to remove that fan, only to find the nuts on 2 of the screws would NOT budge. So I ended up cutting them of with a Jewelers Cutoff disk in my Pencil size tiny high speed drill.

Once the fan was out of the way I was able to see the damage.

Now to fix it.

Looking at the Circuit diagram it says the cap C17 is a 10uF 25vdc one. Further reviewing Circuit I note there are 14 of this value capacitor in the Power Supply,

My NOS of these 10uF are 25v ones and likely 15 to 30 years old.

So I have ordered a 100 new 10uF but 35vdc working and will replace the lot in this MW Otrona and my Otrona and the 3 supplies I have.

This RELIFE Digital Microscope Camera is really great to use and is clear as.

If I recall I have dual lens in tandem on it. One is Adjustable focus, other is a fixed magnification lens: by 2 or by 4 I just cannot recall.

Camera lens is a ZONGMAI Industrial Video Microscope C-Mount lens TV0.75-050 Mag 18 to 130X Working distance 160mm Visual field @0.7x is 30mm and @ 5.6x is 3.6mm

The biggest issue I have with it is, at near to and highest magnifications, it really needs an Exceptionally heavy based sturdy mounting boom, as it moves every so slightly if I knock my workbench.

I did not choose to mount it on a separate floor mount as I need it to be portable. The base block my boom arm is fixed to is 25kg so this stays put. Its just the microscope arms pivot joints have some slight movement.

I will do a separate post in tools forum here on VCFED in due course.

Anyways in the photos you see 3 Otrona's.

One on left bottom is MW's with the 8/16 MSDos expansion board and GPIB. Also it is fitted with 96tpi floppy drives, plus drive select jumper block bought out to a dip switch mounted on drive front

The top one is my Otrona with same expansion board. Plus I cut and added a test slot in front cover below the screen. this slot allows me to plug in the 8/16 or Multifunction card at front of machines to aid testing.
It also has the DC power in option fitted along with 96tpi floppy drives.

The Otrona on right is running stock CPM motherboard. It has that GPIB and A/D and D/A expansion card in it.

This is the first time I have powered up the 2 machines of mine in over a year.

The Otrona on right screen is quite low in brightness, so I need to investigate this later.
For now its connected via its output video jack to the Video Monitor on shelf at left in pic.

My Otrona is not showing any screen display nor am I getting any display when connecting it to that remote monitor.
Not even a drive light on. So I suspect the PSU has failed. If I am lucky its just a fuse. However I will be changing out the 14 10uF 25vdc Tag Tant's before I apply Mains power to it again,

MW on bench 1 .jpg
 
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Thats the Digital Microscope Lens you see in my pics.. I paid Aus$111.60 with free shipping in Aug 2024 for it from ZONGMAI's offical store on AliExpress
1778669825189.png
MW on bench 5 .jpg
 
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Am I getting toooooo OLD ? or are most of the current VCFED forum foke simply too Young now to appreciate a sense of light hearted humor mixed into a deeply technical post here to make any comment or sort of join in.

Yes Computing is 99% digital 1 or 0, yes or no, with so little analog diversity in communicating.

I think this is what has put me off posting as much, if at all, on here quite a while back.

From now on when I post, or more if I post any further on this site, I will have cold black and white factual post.

Perhaps in June when I turn 75, I will give myself a present. A few 30cm dumpster skips and just chuck out all the Technology kit I own; and keep only a few of my old books from the 1800's.

I might even take up learning to cook.
 
inotarobot said:
Am I getting toooooo OLD ? or are most of the current VCFED forum foke simply too Young now to appreciate a sense of light hearted humor mixed into a deeply technical post here to make any comment or sort of join in.
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I saw the humor but didn't come up with any witty saying to reply. Nice that you went over the tools. Your digital microscope is better than mine. The large depth of field will make it easier to do work with. I mostly use one of the head worn magnifiers. Also annoying short depth of field. Among the many who have had replaced shorted Tantalum's. Just didn't think I had anything useful to add in reply. Your post was thorough. Poor posts tend to get more replies. Only occasionally remember to use like on posts that are good but I don't have anything to say.
inotarobot said:
A few 30cm dumpster skips
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Convert to real units 11.8". Must not have much :).
 
inotarobot said:
Am I getting toooooo OLD ? or are most of the current VCFED forum foke simply too Young now to appreciate a sense of light hearted humor mixed into a deeply technical post here to make any comment or sort of join in.

Yes Computing is 99% digital 1 or 0, yes or no, with so little analog diversity in communicating.

I think this is what has put me off posting as much, if at all, on here quite a while back.

From now on when I post, or more if I post any further on this site, I will have cold black and white factual post.

Perhaps in June when I turn 75, I will give myself a present. A few 30cm dumpster skips and just chuck out all the Technology kit I own; and keep only a few of my old books from the 1800's.

I might even take up learning to cook.
Click to expand...
Are you going to go back to starting fire by rubbing sticks together?

I turned 65 back in march, and still like tossing a bit (just a bit, not a nybble or a byte) of humor now and then.
 
djg said:
I saw the humor but didn't come up with any witty saying to reply. Nice that you went over the tools. Your digital microscope is better than mine. The large depth of field will make it easier to do work with. I mostly use one of the head worn magnifiers. Also annoying short depth of field. Among the many who have had replaced shorted Tantalum's. Just didn't think I had anything useful to add in reply. Your post was thorough. Poor posts tend to get more replies. Only occasionally remember to use like on posts that are good but I don't have anything to say.

Convert to real units 11.8". Must not have much :).
Click to expand...
30cm is what the rest of the world uses to mean 1 foot, and they have funny sized pints.
 
djg said:
I saw the humor but didn't come up with any witty saying to reply. Nice that you went over the tools. Your digital microscope is better than mine. The large depth of field will make it easier to do work with. I mostly use one of the head worn magnifiers. Also annoying short depth of field. Among the many who have had replaced shorted Tantalum's. Just didn't think I had anything useful to add in reply. Your post was thorough. Poor posts tend to get more replies. Only occasionally remember to use like on posts that are good but I don't have anything to say.

Convert to real units 11.8". Must not have much :).
Click to expand...
DJG at times my being called (labelled) a Polymath a lot over the last 5 to 8 years, has had its positive and negatives to my sanity. My bursts of Humor 'venting' so to put it, are probably better medicine for me than Tai Chi [which I don't do] as a balance to my often technically overloaded mind

Don't get me wrong, I do NOT occasionally wear a pair of underpants on my head when working in my Electrical/Electronics Workshop & on its Computers (like those 2 boys in the movie Weird Science) BUT I do have a small mirror on the shelf above my main workbench to allow me to occasionally glance behind me, hoping to see Kelly LeBrock entering though the door in that movie scene fashion. DREAMS...sigh.

Actually I had never given a though to your statement "Your post was thorough. Poor posts tend to get more replies" Interesting observation thanks !!

""Just didn't think I had anything useful to add in reply"" Thomas you DID have by following on with "I mostly use one of the head worn magnifiers. Also annoying short depth of field"

10 years or more back I used an optical microscope on fine work. leaning over was draining so i tended not to do many repairs that required that level of work. And its depth of field was very small.

I feel the combination of Mobile Phone repair shops coupled with way more surface mount hardware as made the cost of repair tools to suit come down a lot.

I will do a post here under the section Vintage Computer Tools on this microscope, plus discuss the stand and other tools I have got more recently to do board works.

I did appreciate your replying.

by the way CONVERT TO REAL UNITS ROFL I will PAY that humor response. GREAT Comeback Mate

I was tired when I wrote that post and the 30cm was meant to be cubic meters or for the those across the pond cubic yards. so that would have been near enough to a 40cubic yard skip
 
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KE6JAG said:
30cm is what the rest of the world uses to mean 1 foot, and they have funny sized pints.
Click to expand...
Pints ? British liquid measurement for those sitting by a counter (binary glow tube not) drowning their sorrows with a Guiness, at not punting on the Winning "Filly" ( 4 or 2 leg ones)
 
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CloudInMyHead said:
Can you share what part number you ordered for the 100 new 10uF but 35vdc caps?
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Sorry cannot at the moment.

reason is my term 'Ordered' was not mean in the literal sense. I rang and got an associate of mine, to get his ISO9001's certified Companies Purchasing officer to research a range of suppliers for me, to see see whom has stock of Tantalum's and what their manufacturing dates are. Many component outlets, especially smaller ones, have NOS stock that has questionable manufacturing dates. I want fresh, as in last 5 years, made components and not if possible Chinese or like.

I have not kept up with what the state of 'leaded' general purpose electronic components manufacturing is, as compared to Surface Mounted manufacturing, so hence my hand balling it to that PO.

Once I get an answer I will post here
 
Personally, given you can get up to 10uF in Monolithic, I tend to go with monolithic where I can for longevity and lack of long-term issues.

Monolithics are superior in almost every way as DC filter capacitors.

The ONLY time when you don't want that is when you need the characteristics of an electrolytic, eg, higher ESR or larger than 10uF.

The downsides to using monolithic are pretty minor... Minimal loss due to DC bias. Though by 25v, it does creep up, but is it actually 25v continual bias or 12v with a 25v rating?

As a replacement for a tantalum, at least you know it's not going to install any blowtorches in your circuit. Why install an electrolytic over a monolithic is the key question I'd ask?
 
OK, per cj7hawk, maybe I should look for a monolithic. Not sure if these are monolithicor not. I did not see a filter for monolithic.
Theses are from DigiKey. I don't know if the computer will care of the quality or difference between these.

7-Caps.jpg
 
Yep, the cheap kits are awesome... You'll get quite a few spares, though if you don't make anything it's a lifetime supply.

The 10uF should be sufficient. If it's a 12v circuit, you should get around 7uF with the DC bias, but the lower ESR makes them very effective at decoupling.

You can't use monolithic everywhere a different capacitor was used, but they are quite effective for replacing 10uF Tantalums for that purpose.
 
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