"don" <[EMAIL PROTECTED]> made an utterance to the drakelist gang
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Thanks to all for providing this useful tidbit
of info !!
however,
After posting my orginal msg, instead of waiting for
input from those that know, I went out to my shack.
I did see in the manual where the -5v was used in the
if filters, but concerned that the -3 wasn't right, and
worried that it was being used elsewhere that I overlooked,
I now have -5.12v. I carefully removed the top half of the
transformer core, (powdered iron?), removed the un-grounded
leg of supply, added 6 turns to the outside, then counted that end.
Leave it to me to blaze new and path a fix something that wasn't broke!!!!
Its just when the schematics called for the -5v, by goodness, I
wanted -5v!
Do you think the extra may cause problems? I would hate to try to un-fix
it
as the transformer core i believe is very fragile, but I will change it back
if it
will cause damage.
the extra windings by the way, did not change the voltage in anyway on the
25v side.
Thanks again,
don ( that d*#n kid!) frasher
KB5GNH
----- Original Message -----
From: "Garey Barrell" <[EMAIL PROTECTED]>
To: "don" <[EMAIL PROTECTED]>; "Drakelist" <[email protected]>
Sent: Saturday, August 20, 2005 7:51 PM
Subject: Re: [drakelist] tr7 update
Don -
Your -5.0V supply is "normal" at about -3.3 to -3.4V. That is what they
all run. This voltage is only used to back bias the diodes in the IF
filter switches, and seems to be adequate for that service.
73, Garey - K4OAH
Atlanta
Drake C-Line Service Manual
<http://www.k4oah.com>
don wrote:
I got the 3n204 replaced, and put it all back together,
and began to get some response. So I thought I would
start trying the alignment procedure once again. While
adjusting the agc pot to set the s-meter, there was very
little change in level, and nowhere enough to correctly cal
the s-meter.
After checking the schematic, I figured I would check the
easiest things first, which in this case there is 4 diodes, 1n4148's
three of these had very high resistance, but otherwise good. I changed
them out, re-check the agc level, and now have almost
too much!!
At this point, I realized that as hacked-up as this radio is, I really
should start at the begining. I check the PS7, voltage, ripple, all was
great, couldn't be better.
I then go to the power regulator board. what a mess!!!
I removed several diy mods, replaced caps with ones of the correct
values,
etc. Now, all voltages and pb voltage adjustments off this board are
good, EXCEPT,
the neg 5v. I think there is a couple of shorted windings on the small
pcb
transformer, and about the best voltage I get from it is about -3.4, but
only when
the 10v pot is set to well over 10.75v, not good. The radio will begin to
receive with 10v set correctly, but I only have -3v, any lower
and the digtial stops, and no audio. and I doubt the alignment will ever
be correct at such a
low voltage. back now to scratching my head, and trying to figure out a
way to fix, hopefully with re-winding
the transformer, or having to replace the board. Don
KB5GNH
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