Re: SMD rework/repair. Was: Boston area elecronicsurplus.


Kerry Burns
 

There was a DIY reflow PID controller published in the April/May 2020 Silicon Chip Magazine (https://www.siliconchip.com.au/Issue/Browse/Issues ).  I haven’t tried building it, but it seems like a reasonable design.



Kerry



From: <TekScopes@groups.io> on behalf of Thomas Garson <tgarson@auraltek.com>
Reply to: <TekScopes@groups.io>
Date: Tuesday, 1 December 2020 at 11:27 am
To: <TekScopes@groups.io>
Subject: [TekScopes] SMD rework/repair. Was: Boston area elecronicsurplus.



I do SMD rework/repair, on occasion. I determined that a reflow oven was

frequently required as solder connection quality/failure were not

infrequent issues.



I built one based on a modified toaster-oven into which I fitted a PID

controller. It was a PITA to do, but is (now: See below.) much better

than the overpriced low quality available options.



Warning:

If rolling your own reflow oven is in the cards, make sure the

thermocouple is located in the upper area of the chamber and is naked.

Do not use an enclosed probe because the response time is too slow. I

did, and cooked the first board I used it on (fortunately not a

customers board). Perhaps the toaster-oven I chose had too much power

compared to a "factory" reflow oven. A lower power oven might have been

a good choice but I wanted one that had a large chamber. It might be a

good idea to determine the temperature rise and cooling rates of your

oven candidate prior to wiring up the heating elements, using fewer if

they are overkill. You might have to add a cooling fan to the enclosure

to assure proper cooling rate after the solder flow temperature is

reached. A lot of parts don't like to spend much time at the solder flow

temperature. If you use a convection oven, it might be possible to

modify the fan shroud to pull in outside (cooler) air.



For sure, there are high quality industrial grade reflow ovens

available, but at too steep a price for my budget.



Thomas Garson

Aural Technology, Ashland, OR

By my calculation, the dynamic range of the universe is roughly 679dB,

which is approximately 225 bits, collected at a rate 1.714287514x10^23 sps.

On 11/30/20 2:47 PM, Shirley Dulcey KE1L wrote:

Sadly, nearly all of those Boston area stores are gone. You-Do-It

Electronics is still open; it now has a significant selection of maker

stuff from Sparkfun and Velleman (and a few Adafruit items) along with the

usual TV repair parts, enclosures, cables, and so forth. Oddly, they

haven't embraced SMD technology at all; they don't even have rework

stations or solder paste. I guess their primary customer base doesn't do

any SMD repair; those boards are considered unrepairable at this point.



On Mon, Nov 30, 2020 at 5:03 PM stevenhorii <sonodocsch@gmail.com> wrote:



I never did get to Meshna's place or B&F but I bought stuff from both via

mail order (the forerunner of online shopping). I think it was a WW

II passive infrared night vision unit I got from Meshna - I could be wrong.

Years later, I discovered that the technology for that wound up being a

fundamental patent that evolved into the first replacement for x-ray film;

storage phosphor plates that stored the x-ray "image" as electron

metastable states in a phosphor layer. Hitting the plate with a scanned

laser would push the electrons out of their metastable state and they would

drop down to ground state giving off light photons as they did so. A

photomultiplier would digitize the intensity of that emission thus was born

the photostimulable phosphor plate radiography system. The story is that

Kodak had the patents for the phosphor system but did not want to kill off

their x-ray film business, so they sold the patents (or licensed them) to

Fuji Medical (the Fuji film people). Fuji Medical produced the first

clinically used phosphor plate radiographic system. The use of x-ray film

declined very rapidly after that.



The last item I bought from B&F when I think it was just Frank Fink was

running the business - it was a militarized DEC PDP-11 built by Norden

Systems under license from DEC. I still have that thing - two two aircraft

avionics type boxes, a mess of cables, and the "control box". A bonus - all

the schematics. It was some version that I think had been used for software

and peripherals development as it runs on 115VAC 60Hz instead of 400Hz. It

runs or at least powers up with no smoke. The control box has two switches

on it - not the nice PDP-11 panel with all the flashing lights and

switches. It basically says "Run" and "Halt". That's it. I found the core

memory modules (they had been removed from the unit I bought) at a hamfest

(the one that used to be in Gaithersburg, MD) and installed them. If there

was any programming left in them, it didn't run so far as I know.

Interfaces are in the form of multipin mil-spec connectors - very expensive

to find mates for.



I used to go to Ron Baublitz's US Surplus in Baltimore. Four floors of a

huge amount of stuff. I think US Surplus may still be around, but they sold

off the building. It was across the street from the B&O Railroad museum. I

also went to Bid-Service in Asbury Park, NJ. It has transformed into a

business that sells used semiconductor fab equipment and are now in

Freehold. It is, I believe, run by the same family that ran the old

Bid-Service run by Bill Cusa. I first met Bill when I had him pick up a lot

for me that I won on a DoD surplus sale. I then drove down to his place to

pick the stuff up and he asked if I wanted to see the stuff he had in his

warehouse. He had started as a business selling used restaurant equipment,

but since he had the trucks, he branched out into the pickup and ship

business for bidders on DoD and GSA sales (hence the name). His initial

inventory came from the packer-shipper business. Often bidders would win a

lot, but only wanted one item. They would often tell Bill he could keep the

rest or at least offer it to him if he'd discount his pickup fee. As a

result, he had a large amount of stuff from those DoD sales. He hired some

guys (one of them his son) who quickly learned about test equipment and

they started bidding on local auctions and sales themselves. I once went in

on a bid with Bill on a complete radiographic/fluoroscopic system being

excessed from the West Point clinic. We won the lot, but my advice to him

was to sell it to a medical remarketer as we did not want the liability or

FDA issues. We still made money - that system was a top-end one that was

still being sold by the manufacturer.



There was another surplus dealer south of Baltimore. I don't remember the

business name, but the owner was Gary Green. Another huge place full of

stuff. You could get all manner of test equipment (yes, including Tek

scopes and plug-ins). Bargains were large mil-spec transit cases - the

large, weather-tight Hardigg ones. Any color you wanted as long as it was

olive drab. Not exactly true - there were white ones also. I was only there

once, but spent the whole day. I bought a Efratom rubidium frequency

standard - worked when I got it. I have not needed it in a while, but I

still have it.



When I think about it, I spent a LOT of weekends climbing around piles of

surplus, or walking through miles of storage racks full of stuff. I used to

have dreams about going to surplus stores and finding something exotic.

Always disappointed to wake up and find it had been a dream!



Steve H.







On Mon, Nov 30, 2020 at 4:17 PM Dick <w1ksz@outlook.com> wrote:



There was also Electro-Craft on Dorchester Ave (in Dorchester).

Tons of NIB ARC-5 Receivers and Transmitters.



73, Dick, W1KSZ

"Dahchester" Boy, 1940-1966

________________________________

From: TekScopes@groups.io <TekScopes@groups.io> on behalf of Brad

Thompson <brad.thompsonaa1ip@gmail.com>

Sent: Monday, November 30, 2020 2:13 PM

To: TekScopes@groups.io <TekScopes@groups.io>

Subject: OT: Boston-area electronicsurplus (was:Re: [TekScopes] Fair

Radio

Sales Lima Ohio)



tekscopegroup@miwww.com wrote on 11/30/2020 12:28 PM:



I recall walking Canal Street in lower Manhattan in 1976 during a

vacation trip with my parents.



<snip>

Hello--

Sometime in the early 1960 , my roommate and I hitchhiked from Boston to

his home near Suffern, NY-- his goal was to see his girl friend, and my

goal was

to visit Radio Row in NYC. I didn't have much spare cash and I don't

recall buying

anything <:. I do recall visiting Barry Radio at 512 Broadway, IIRC.

Construction

of the World Trade Center was on the horizon and the surplus stores were

beginning to close.



Fast-forward to the late 1960s-- I had graduated from college and had a

job in

Bedford, MA and a little more spare cash. On a typical Saturday, I could

drive

into Cambridge and visit Heffron's surplus junk yard. From there, I'd

head north to Rte. 128 and stop in Wakefield to shop at Poly-Paks ("We

bot <sic> thousands,

no time to test!") (*)



From there, Meshna's surplus in Lynn was always worth a stop, and on

one occasion

I was invited to visit the warehouse's basement-- filled with

boxes of surplus stacked from floor to ceiling and threaded

with shoulder-wide paths (think, 'mouse trails through a meadow').



There's still gas in the tank and cash in my wallet, and B+F Electronics

near Salem (?)

was my next stop. (B + F were Pete (?) Boniface and Frank Fink).



Finally, there was a four-story brick warehouse near Newburyport. MA,

which wouldstill had glass in most of its windows. On one occasion,

I reached into a box of miscellaneous parts and pulled out a skinny white

cylindrical object. Closer investigation revealed the remainder of the

pigeon skeleton.



Time to go home.



There were a few conventional electronics shops that sometimes offered

surplus

parts-- Abbott Electronics in Woburn, and a shop that moved into Malden

from Atlantic Avenue in downtown Boston. Radio Shack's store on

Commonwealth

Avenue could offer an occasional bargain.



Further out in the suburbs, You-Do-It electronics sold little in the way

of surplus

but was the go-to site for unmolested components. Herbert Gordon (W1IBY

(SK))

sold used ham gear and surplus in Harvard, MA, and offered opinions.



I apologize for omissions and errors of location-- fifty years of recall

imposes a layer of haze on some memories.



73--



Brad AA1IP



(*) In practice, it was possible to buy functional components there, but

sorting through a batch of Transitron rejects and testing them

was very educational.

Join TekScopes@groups.io to automatically receive all group messages.