Re: Suggestions for rehabbing a 466 w/ DM43

Fabio Trevisan
 

Hello Ryan,

It seems we're almost in sync regarding the repairs we're doing, you to
your 466 and me to my 464, which are mostly the same.

I just finished refurbishing the Scale Illumination assembly on my 464 and,
as though I had to remove the A6 Interface board out (for other reasons), I
could see that there's actually nothing that prevents pulling that assy'
out, besides its own 2 pin header (harmonica header) P1791 being attached
to the A6 interface board, just next to its controlling transistor Q1792.
Just pulling out the header connector already make the assembly loose and
allow you to pull it out (the 2 wire cable is short).

The problems you may face (if your storage controller board isn't removed
yet and if you don't plan to take it out) are:
1. To move / slide the 2 pin header between the Interface board and the
Storage board, so that it can run freely underneath the Storage board...
2. To run the wire and header back into place, after you clean / refurbish,
do whatever you need to do to the lamp assembly.

For problem 1, my advice is that you just take the pins out of the header's
plastic holder... without the holder and the 2 pins separate from each
other, is much simpler to slide them under the Storage board and pulling
out the lamp assembly from the scope's front (BUT WAIT, don't do it before
reading below)...

For problem 2, I advice you to attach (with scotch tape or insulating tape)
some thin leader to the tip of the lamp assy wiring, so that you can pull
it back afterwards.
One of the wires from a piece of rigid CAT5 network cabling will do nicely.

I did replace my lamps for 10cms worth of flexible LED stripes (6 leds, two
segments of 5cm) and I`m almost ready to post the pictures of the whole
process, at the TekScopes photo area.
To account for the fact that the LED stripes work with 12Volts, and also
for the fact that LEDs are more dimmable by controlling their current
instead of their voltage, I modified slightly the lamp control circuit,
turning it into a variable current sink, instead of a variable voltage
source.

The modification is 4 steps:
1. remove P1791 (2 pins) altogether and mount a 150Ohm 1/3Watt resistor in
there (150Ohms yields about 42mA under 6.3V which is just over the LED's
nominal current of 20mA per 5cm).

2. Change the voltage source of Q1792, from +5 UNREG to +15UNREG, by
cutting the track to the collector of Q1792 at 2 places...near the +5V
UNREG rectifier bridge and near Q1792 itself.
2.a. 1st cut near the rectifier bridge CR1761 (on the component side), It's
a less than 10mm segment of track between the bridge and a via.
2.b. 2nd cut near the Q1792 itself, leaving some space around the cut to
solder on both sides before and after the cut. (e.g. don't cut right near
Q1792 collector, but some 5mm away)

3. Connect, with a 3.5cm piece of insulated wire, the +15V UNREG voltage to
the via (mentioned on point 2.a. above). This will bring approx 23V on top
of the led stripe (instead of the original 10V from the former +5V UNREG).
Since Q1792 is rated for 40V there's no problem here and dissipated power
won't be a problem either, as the LEDs will draw only one tenth of the
current of the 2 lamps set.

4. For this, I used 2 pins from a right angle pin header, but any thicker
component lead will do (0.6mm dia), and pulled out and reinserted the pins
so that each L points outwards, and soldered the headers FLAT, right on the
track near Q1792 transistor, so that each pin is soldered on each side of
the cut performed on step 2.b.

I tested it already and it illuminates the scale bright and evenly all the
way through the screen's height... million times better than the uneven and
weak illumination from the original 2 lamps set.

Rgrds,

Fabio





2017-05-08 14:17 GMT-03:00 Ryan Stasel rstasel@... [TekScopes] <
TekScopes@...>:



Hi Everyone,

Thanks so much for the input on this. Some Deoxit later, and I have a
largely functional scope with two remaining issues (one being recapping the
PSU and main board).

The other being replacing the graticule illumination lamps. I can’t figure
out how to get them out… they’re in a holder, which has seen better days
(being plastic from 1976). But the cord that powers them runs into the guts
of the scope… Do I really have to pull the whole thing apart?

Thanks!

-Ryan Stasel
IT Operations Manager
School of Journalism and Communication
University of Oregon

On May 3, 2017, at 21:24 , Fabio Trevisan fabio.tr3visan@...
[TekScopes] <TekScopes@...> wrote:

David,
Yep, essentially that is the idea but the solder doesn't actually need
to
touch the board (although it doesn't hurt either).
Since molten solder has a high surface tension, you fill the crucible
with
enough solder so that the molten solder surface is above the crucible
edges
so, when you get the board closer and closer, the solder touches first
the
tip of the components and it's surrounding solder... In that moment, the
solder around the leads immeditaly melts and is "pulled" by the
Crucible's
solder (by capilarity or surface tension, I'm not sure exactly what's
the
name of mechanism by which it happens).
You don't actually need to take the board closer than that because at
this
point, the solder around all pins is already molten and the component is
free to be pulled from the other side.
In practice you apply some pulling force to the component before and as
you
get the board closer and closer to the crucible.
At some point the component gets free and comes out and you can lift the
board away from the crucible.
If you apply some flux to the board before is even better as it helps
the
molten solder to "wet" the pins/pads.
When you lift the board, it leaves the pads with an even and thin solder
coating.
Large holes are drained out and smaller holes remain filled with solder
as
the hole's capillarity "hold" the solder inside them.
As with everything else, some practice is required and you can train
yourself on scrapped PCBs of any unrepairable device or equipment, such
as
of computers, laptops and modern scopes :-).
Kidding... One cheap stuff that is often discarded such as desktop PC
power
supply boards usually have the kind of bigger components (like big
transistors hooked together with their solderable heat sinks) that allow
you to get the "touch" quickly.

Brgrds,

Fabio

On May 3, 2017 10:01 PM, "David Berlind david@... [TekScopes]"
<
TekScopes@...> wrote:

So, the PCB essentially had to make contact with the melted solder in
the
crucible?

On May 3, 2017 8:07:40 PM "Fabio Trevisan fabio.tr3visan@...
[TekScopes]" <TekScopes@...> wrote:

Hi David,
I didn't but I wish I did because now I'm having to work around quite
a
few
lifted pads and stripped-off metalized vias.
I do have, however, experience of a former job at a computer
manufacturer
in Brazil where we had small crucibles, of about 3 cms diameter, to
unsolder hard stuff just like this... Multi pin connectors where the
pads
were big (and retains a lot of solder and drains a lot of heat) all
that
were a pain to remove by any other means, and were so easy to remove
using
the crucible.
It was just a matter of carefully turning the PCB solder side down
over
the
crucible so that it would melt all the pins simultaneously, wait for
no
more than 2 seconds and pull the connector away.
They would come out so quickly that we could hold the connectors bare
handedly.
Of course that it has its down side...
It takes you to remove the board (which is not easy on the 4xx series
scopes), and sometimes takes additional measures such as removing
components around the area where the crucible will have to get close
to
the
PCB, either not to damage the components or to clear the area so that
you
can actually put the board in contact with the molten solder.
Back then, at a factory, we did that simply because it was faster and
cleaner, and usually there wasn't the down-side of having to
disassemble
the equipment, because it was already disassembled.
At a repair shop, dealing with equipment that's still current, I think
it
wouldn't be practical for the day to day use, due to the down-sides
and
due
to the availability of parts to replace, should they get damaged in
the
removal process..
Back to the restoration business (where we are) when a PCB that is, at
least, hard to get, and when you also don't want to destroy the old
caps,
because you want to use their packaging as mechanical support for the
new
ones, as I had to, I think that the additional preparation work is
worth
it.
I wish I had a small crucible at hand when I started removing the
caps.
But I fooled myself I would do it easily and I must confess I regret
for
having insisted on doing it the hard way.
Later I went on looking for crucibles and found small ones for as
cheap as
Brazilian 110,00 which is roughly 30,00 dollars.
I will look after one to have it around for the next occasions.

Brgrds,

Fabio


On May 3, 2017 7:06 PM, "David Berlind david@... [TekScopes]"
<
TekScopes@...> wrote:



Hi Fabio,

I suspect that I will one day end up having to recap my 466... I was
curious about this statement:

*"get yourself asmall soldering crucible... because it takes too long
to
unsolder thecapacitors using regular solder wick and solder
vacuum-pump
and
the PCBsuffers. It's almost impossible not to end-up lifting some
pads
and/ortracks or ripping-off some of the metalized thru holes
(vias)."*

Can you explain how specifically you ended up using the crucible?

Thanks.

On Wed, May 3, 2017 at 5:43 PM, Fabio Trevisan
fabio.tr3visan@...
[TekScopes] <TekScopes@...> wrote:



Hello Ryan,

I have a 464 (they're quite similar to the 466, exception to the
H.V.
section that is simpler than that of the 466s) which I have went
through
all sort of minor problems since I bought it about 9 months ago.
Last "event" was that if finally blew one of its large P.S.
electrolytic
capacitors, the 1200uF x 120V.
On this last event (quite recent), I posted a question on this
forum,
for
which I had quite some good advice from the folks.

Search for the thread:
Tek 464 - Big Caps recommnedation - Pot grease recommnedation

The original caps "form factor" is not in use presently and most
you
will
find on the market are plain "Radial" caps, (with plain leads) or
"Snap-In"
caps that are usually short and fat (and some of them won't fit on
the
1"
available space).
Neither fits-in mechanically / physically as the originals and both
require
some adaptation.
In recapping yours, you will have to make up your mind on either
following
the path of that guy you mentioned who recapped his 465 with
Snap-In
capacitors (and connected them with wires and held them with
plastic
brackets)... Or...
Buy pairs of smaller valued capacitors and mount them "In" the cans
of
the
original caps (after opening them up and disposing their original
innards).

I followed the latter path and I`m just about to finish doing
it...As
soon
as I can I will post to the pictures area of Tekscopes.
My solution was as follows:
500uF x 50V was replaced by 820 x 100V (it fits inside the can).
250uF x 150V was replaced by 330uF x 250V (if fits inside the can)
3 x 5500uF x 30V were replaced by 3 pairs of 3300uF x 63V (and each
pair
fits well inside the can)
1200uF x 100V were replaced by a rather long pair of 680uF x 160V
(I
wish I
could have found shorter ones) They were 2 inches tall (each) and
the
association didn't fit inside the can and I had to open the top of
the
can
to mount them inside.

You will notice the C and V values are larger in all of them than
the
originals, and this is not by chance. It's rather an advice from
the
folks
of this forum to make up for the overall smaller ripple current
ratings
of
the modern electrolytics.
Another advice is to try to have them all of 105C grade (the
original
ones
were all 85C).

Last but not the least, on desoldering the old ones, if you plan to
follow
the 2nd path (and re-use the old capacitors base and cans), get
yourself
a
small soldering crucible... because it takes too long to unsolder
the
capacitors using regular solder wick and solder vacuum-pump and the
PCB
suffers. It's almost impossible not to end-up lifting some pads
and/or
tracks or ripping-off some of the metalized thru holes (vias).

If you don't plan to use the older capacitor bases and cans, its
better
to
just cut the old ones with a dremel cutting disc and pulling the
terminals
one by one.

Rgrds,

Fabio

2017-05-03 17:17 GMT-03:00 Ryan Stasel rstasel@...
[TekScopes]
<
TekScopes@...>:




Hi All,

I picked up a Tek 466 w/ DM43 locally for $30 this week, and
after
replacing the main fuse, it powered up, and after fiddling with
things
for
a while, it’s mostly “working”. Checking all the voltages, things
seem
good
and within tolerance. But it’s obvious all the caps are original
to
the
unit… which, I have no good date on since I can’t find a serial
anywhere
(there is a hand written label on the tube shielding that says
92615).

Anyway, it’s pretty clear all the switches and pots need cleaning
(do
most
suggest just using Deoxit spray, and maybe Fader Lube for the
pots?),
and
the main caps need replacing. I’m also seeing a couple axial
electrolytic
caps on the “main” board (looking at the screen, the board along
the
right
hand side) need replacing (they’re showing corrosion on the
leads).
But
I’m
also curious if I should pull any of the socketed transistors or
ICs
and
spray the sockets with cleaner and reseat, etc. The unit still
acts a
bit
weird from time to time (screen blooms like it’s doing some
storage
mode,
not showing both traces, not properly grounding the inputs when
gnd
is
selected, etc).

I’m happy to link to pictures, etc… everything looks good, but
obviously
hasn’t been touched much since the unit was built. I’m also
really
interested in what caps I should use for recapping the Power
supply.
They’re a very odd size (tall and skinny), and looking online, I
see
someone recapped a 465, but the new caps didn’t really match in
size
at
all
so jumpers were needed. I’m pretty sure these size caps aren’t
really
made
anymore, so I’m all for suggestions.

If anyone’s interested, it looks like my unit was tested by a
Kreurauko
(or something like that)… and the DM43 has “Donna” written on the
board
in
“Sharpie”. =)

Thanks very much!

-Ryan Stasel




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