[GreenKeys] ST-6 Up & Limping On The Work Bench

[tony.podrasky]

Hi Ralph et al;

Well, - Irv Hoff says that the LM309s can be pretty squirrely,
and when you build the ST-6 you might have to shuffle some of
them around until you find one that works.

There is also some really weird things going on with the unit:
I find it hard to believe that there is a wiring error - since
this appears to have been wired by HAL - but
the 850Hz stuff works backwards with the autostart: instead of
going online with MARK condition, it does it in SPACE. The 425Hz
board goes online with either MARK or SPACE. The 170Hz stuff is
just plain old dead.

I'm going to have to print out a copy of the schematic and start
doing some point-to-point checking.

I'm a GREAT ENEMY of taking something that works (my current ST-6)
and using its parts to trouble shoot the "new ST-6": I spent 30
years in the computer industry as a field engineer and much of
that time repairing TWO units because the newbies, who really didn't
understand the design and technology, were taught to SWAP things
until it worked. That sounds "good on paper" - and certainly can
pump-out technicians from a trade $chool - but all you need is for
the last guy who used the kit to "forget" that he put a defective
part in it, and turn it into the depot. Then, when the next "kid"
signs it out, the fun begins... I spent the last 10 years of my
career repairing what they broke - and putting up with customers
that were cranked-off at the quality of service they were getting.

UE,
K2EAA - TONY
NNNN
ZCZC

On 03/14/2016 08:08 PM, Ralph Mowery wrote:
> It may be that some of the resistor values have changed or maybe the
> wrong values were installed when it was built.
>
>
> ----- Original Message ----- From: "tony.podrasky"
> <tony.podrasky at gmail.com>
> To: "Green Keys" <greenkeys at mailman.qth.net>
> Sent: Monday, March 14, 2016 8:36 PM
> Subject: [GreenKeys] ST-6 Up & Limping On The Work Bench
>
>
>> GE OMs;
>>
>> I finally got motivated enough to go into the garage
>> cabinet and get out some of the stuff to tune-up the ST-6.
>>
>> Used rubbing alcohol on the loop current rheostat and she's
>> working nice and smoothly.
>>
>> Tried to do the NULL adjustment on the 2 discriminators,
>> but couldn't do it. I swapped the LM709 Op-Amps, and one
>> of the boards could balance, but the other still can not.
>> I swapped a couple more ICs and didn't have much success.
>> Went on "everyone's favorite auction site", and although
>> some of these "1970's ICs" are selling for $7.00, I
>> found a NOS bag of 15 for $12.00.
>>
>> They should be here some time next week.
>>
>> More updates as they happen...
>>
>> UE,
>> K2EAA- TONY
>> NNNN
>> ZCZC
>>
>

-- 
Great truths about life that little children have learned:

  "Never hold a Dust-Buster and a cat at the same time"