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Author Topic: Astron RS-35A: rebirth? after lightning  (Read 3815 times)
WB6DGN
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Posts: 584




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« Reply #15 on: December 20, 2012, 07:13:16 PM »

Quote
I did a similar thing to a Pyramid supply.  However, I made the sink out of one large aluminum stock angle piece...

Nice idea.  I'll "borrow" it if the situation comes up again.  A bit less work too.
Tom
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KA4POL
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Posts: 1907




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« Reply #16 on: December 20, 2012, 09:59:13 PM »

While the product you were looking for is no longer available, take a look at these related items.

Seems they already ran out of this nte electronics to 3 style transistor insulator.  Angry

Just found out, they are only selling in the US. There you can get them.
« Last Edit: December 20, 2012, 10:04:46 PM by KA4POL » Logged
WB6BYU
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Posts: 13017




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« Reply #17 on: December 21, 2012, 06:42:14 AM »

I worked on a commercial project where a supplier was in a rush to build a board and
ship it to us.  The day before it shipped they discovered that the voltage regulators
hadn't been insulated from ground on the circuit board as the design called for, and
they didn't have any insulators in stock.  An enterprising ham on the team called
around to his buddies and they dug out enough insulators from their junk boxes
to make it work in time.

TO-3 insulators are still available new from a number of sources, and can also be
obtained from junked equipment.  But the older mica ones are being replaced by
silicon-impregnated materials.
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AC5UP
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Posts: 3822




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« Reply #18 on: December 21, 2012, 06:58:25 AM »

Seems they already ran out of this nte electronics to 3 style transistor insulator.  Angry

Not surprising.... Nothing says Happy Holidays like a TO-3 insulator.   Makes a great stocking stuffer...!
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W4VR
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Posts: 1190


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« Reply #19 on: December 21, 2012, 08:34:41 AM »

I also took a hit on my 35M and replaced the same components you did plus those in the crowbar circuit.  Works fine now.
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N4EF
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Posts: 31




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« Reply #20 on: December 22, 2012, 07:26:53 PM »

I sincerely grateful for all the suggestions and handholding!  I want to give all the Elmers a status report at this mid-point in the process, as I'm sure it'll help others.

I now have a massive dummy load for power supply testing, by the way.

Here's what I've found from all of the helpful suggestions:

The voltage across D5 drops under load conditions. This is contrary to Tanakasan's  results if D5 was good.

The remainder of the testing below indicates the LM723, 1n1184a silicon rectifier diodes, and the filter caps ( two 32k filter capacitors) show to be good. Specifically: 

The voltage between pin 12 and pin 7 of the LM723 drops only a little when tested under load conditions. 

Moving the + lead to LM723 pin 10 shows voltage increase under load conditions vs no-load.

The 1n1184a silicon rectifier diodes are good.

There is no voltage sag at the + terminal of the filter caps: voltage is steady under load and no-load conditions.

I tried two LM743's and still get voltage drop under load testing.

The voltage at each pass transistor emitter is the same at 1.19 volts.

So, this eliminates some more of the components as being bad, and next on the list is to test the Q2  TIP29A and D5 1N4002.
Thanks for the help and the learning process support.

Dave

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W9GB
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Posts: 2597




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« Reply #21 on: December 22, 2012, 07:50:41 PM »

Quote from: AC5UP
Sears isn't exactly Sears any more...
It's Eddie Lambert land .... Live here in Chicago area, so always hear what's going on with them.
The web presence is a feeble attempt to be Amazon like.

Sadly, the founders (and largest) of mail-order:
Sears and Montgomery Ward, later Spiegel are gone --
 Amazon's success is in reworking the mail-order and logistics formula for Internet age.

Quote from: KA4POL
Seems they already ran out of this NTE Electronics TO-3 style transistor insulator.
MCM Electronics has the NTE TP0001 in stock, $1.66 qty 1.
http://www.mcmelectronics.com/product/NTE-ELECTRONICS-TP0001-/TP0001

NTE’s thermo pads do away with the old-fashioned mica wafer and conductive grease method of mounting power semiconductors. These thermally conductive insulators offer low heat transfer resistance while still providing high electrical isolation between the parts of the assembly.
« Last Edit: December 22, 2012, 08:01:23 PM by W9GB » Logged
W6EM
Member

Posts: 710




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« Reply #22 on: December 22, 2012, 08:21:36 PM »

My money's still on the TIP29....

As for the agonizing earlier about TO3 insulators, most of the surplus outfits selling to hams carry them.  What gets a bit frustrating is the "normal" practice of hitting you up for a 1 lb UPS charge.  Makes a 10 cent part into an $8.10 part.  Ouch.

Both Digikey and Mouser will ship first class or economy-hybrid UPS/USPS.
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W6EM
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Posts: 710




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« Reply #23 on: December 22, 2012, 09:01:41 PM »

Not to prolong an assertion, BUT, Mouser has some 10,000 of the Keystone mica TO-3 inulators in stock.  14 cents each.
The Kapton polymeric ones, are a mere 78 cents each.

So, which would you rather have, 100 mica ones for $8.40 or 10 of the newer Kapton ones for $7.80 from Mouser?  My money's on mica.  Plus a small tube of the white zinc-oxide-bearing grease.  They stopped using beryllium-bearing grease quite some type ago.
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KA4POL
Member

Posts: 1907




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« Reply #24 on: December 22, 2012, 11:30:29 PM »

The voltage across D5 drops under load conditions. This is contrary to Tanakasan's  results if D5 was good.
That sounds strange. You should measure .7 V across this diode if we understand the same one connected from Q2 emitter to Q102 base.
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W6EM
Member

Posts: 710




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« Reply #25 on: December 23, 2012, 05:38:45 AM »

The only way to "guarantee" full saturation across a PN junction is to supply adequate current.  If you don't, then the voltage will drop into the active region at points below the knee.  If Q2 cannot supply the current to saturate the diode in series with its emitter, well.......... a bad Q2 or regulator chip.  A telltale of trouble ahead of it.
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N4EF
Member

Posts: 31




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« Reply #26 on: December 23, 2012, 05:46:14 AM »

Okay: I'll measure D5 again.
 I think I'm getting it narrowed down and thanks to all as I've re-learned a bit since my novice and general days in the 1970's when I had ample time as a teenager to dig into things with big tubes, heavy wires, and hefty switches. 

When decent paychecks (and surface mounting) came along later, it became convenient to let someone else fix it.

Dave
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