[Kenwood] TL922A help

[chuck via Kenwood]

And check the pins on the tubes.  Overheated, they can become partially or completely unsoldered.
 
73
Chuck
W4MIL
 


  
チャーリー ミルトン 
 


 

 
 
-----Original Message-----
From: George via Kenwood <kenwood at mailman.qth.net>
To: Ray Keefe <K2RJK at VERIZON.NET>
Cc: kenwood <kenwood at mailman.qth.net>
Sent: Mon, Apr 27, 2015 11:31 am
Subject: Re: [Kenwood] TL922A help


Also check your socket for burned contacts and overheated springs that don’t
grip the pins.
George NE2I


On Apr 27, 2015, at 7:47 AM, Ray Keefe
<K2RJK at VERIZON.NET> wrote:

> Greetings to those who are much smarter than me.
I recently picked up a nice clean, supposedly working TL922A.  Plugged in on the
bench to check it out with no radio attached.  Yes, I should have put it on the
Variac first and yes I declined the offer to test drive it at the sellers home
b4 I bought it.
> 
> The amp was in standby and set for CW. Hit the power
switch and was greeted by SNAP, CRACKLE, POP, SIZZLE and HUM. Killed the power
within 1-2 seconds. I know now why it was humming, it's because it didn't know
the words to the song it was trying to sing.
> 
> Opened it up. Reconnected it
this time on a Variac. Watched one tube filament get nice and bright, the other
dim. Smelled something getting warm this was at about 50vac input. Grabbed an IR
thermometer, found the filament trans getting very hot 105f+. Shut it down
again. Did more digging.  Looked closely at the tubes the dim one grid folds
looked discolored, possibly from overheating. These appear to be the original
tubes from what I can determine from the date codes and paper work that came
with the amp.
> 
> Found C3 shorted, replaced it, bias/alc/relay voltage ok
now just around 100vdc with little a/c ripple on it.
> 
> Looked further and
found L7 470uh choke blown out. Figured now it had a grid to filament short,
took out C3, D1 checks ok. R22 checked a little low 3.9-4.0k. Located local
source for the choke.
> 
> With each step forward a new issue develops. Now
with the hv safety defeated and no load/tubes installed. Started bringing up the
ac again. At about 50vac, the panel meter shows about 100vdc, and a humming
emits from probably the hv trans. Grabbed my IR thermometer and started probing
the cap bank. Found R16 & R17 hitting 100f+ all the others 65F room temp. Ah,
bad cap. Pulled the cap bank out, clipped one side of each resistor, all check
at 47k as marked. Checked the caps on VOM, all slowly charge. Checked them all
on my old Eico cap tester, all open the eye at rated voltage.  No I don't have
an ESR meter.
> 
> Now that junction is where the CW/SSB tap of the HV trans
connects. Any ideas of where to look next. I know I need at least one tube, the
RF choke, I was about to order a cap bank from Harbach, but now put that on
hold.
> 
> Sorry for being long winded here, but wanted to get as much info
out as possible. Reply to me off the reflector is ok too.
> 
> Thanks for any
ideas.
> Ray
> 
> -- 
> Check out my shop for handmade items for ham radio
operators http://www.etsy.com/shop/TheWoodenHam See more completed work on
Facebook The Wooden Ham
>
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