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SX-1000TW Startup Crackle

moodyj2000

moodyj2000

Member
7E5ED062-16BD-46F8-85C8-850EF86C6E88

7E5ED062-16BD-46F8-85C8-850EF86C6E88

SX-1000TW
Just beginning to look at this unit. Cleaned the pots and everything flows smoothly. Already brought it up with Variac and DBT with no issues. Upon turning it on there is a loud crackle that stops immediately after a second.

No obvious problems on visual inspection. I have a scope, dummy loads and signal generator but waiting on some hookup pieces to get that all running.

I took a look at the output transistors and noticed they are not original. Any thoughts on these and where I might begin troubleshooting?
 
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The Power switch can be problematic on the SX-1000 (any version). Check to see if the dial lamps flicker when the crackling is audible. If so the contact points are arcing due to contaminants. you'll need to gain access to the switch points and clean them. There are more than a few threads on cleaning the power switches on the SX-x50 series (switch is similar). SX-750 seems to have more known problems with this.

OUTPUTS: The GE's are Aftermarket, the Hitachi's are OEM.
 
The service manual list the output transistors as 2SC793. The Hitachi's above are 2SC897 and the GE's are 7221. The recommended replacement for the 793's, which is the MJ21194G, are backordered until late 2023. Any other options?
 
Larry, I promise I thought I looked that up before posting. Thanks again for keeping this Navy Nuke pointed in the right direction. Now if I just had and abundance of time......
 
There's NEVER enough time. You didn't learn THAT during Quals? :whip:
 
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Trying my best to forget quals. Actually, you should have an electronics qual card. Enough people have already come to you for advice anyway!
 
Too much Math. Algebra gave me migraines in High school. Still does. Tubes I can figure out. Solid state locks me up faster than an S5W can drop rods, if it's more than basic T.S. I'd rather dive San tanks. :biggrin:
 
Having served on the BIG E I am more of an A2W guy myself. Being that I was a MM means it is all Greek to me but I haven’t blown anything up yet…..
 
Mine was scrapped in '94 (Casimir Pulaski SSBN 633 Blue). But I have a WWII surrogate (Diesel) in Baltimore Harbor been volunteering on since '98. Got a couple of 38D-8 1/8 10 cyl FM's you can play with.....:biggrin::biggrin:
 
Hate when old boats/ships get scrapped but I guess it’s inevitable. Mine has been parked in Newport News since 2010. Just sitting there.

Back to the SX-1000. Crackling is getting better with some cleaning. One thing I noticed is a considerable amount of transformer hum after startup. Any thoughts of what could be causing that? It is a decent level. Noticeable even with the wood case back on.
 
The power transformer may not like the inconsistent supply voltage and the resulting phase current surges to its primary. As a temporary test, you might consider jumpering both poles of the power switch and operated the unit from a switched multi-outlet strip or similar switch.
 
In addition to Watthours comments, If the transformer is on rubber grommets, they may be failing (crushed, crumbling, etc.) If not, the mounting bolts may be loose. If the Laminations/endbells are bolted, tighten them up.
 
moodyj2000 said:
Hate when old boats/ships get scrapped but I guess it’s inevitable. Mine has been parked in Newport News since 2010. Just sitting there.
Click to expand...

You guys are spoiled. The closest examples around here are a Type 9C German boat sitting dry in Chicago and a Gato in port in Wisconsin. Ironically, of all the boats built in Manitowoc, the one on display there came from Groten. At least it should last indefinitely in the cold fresh Great Lakes water instead of a brine bath.
 
Watthour; Cobia(SS-245) & U-505. Been on both. I DO have Torsk (SS-423) in Baltimore, which I've worked on since 1998. Manitowoc literally built their 28 boats to Electric boat's plans, as a follow on yard. Mare Island did the same with plans from Portsmouth Naval Shipyard.
 
Continuing saga of this receiver. I have POS audio signal generator but I played around with it to get a decent sine wave. Hooked it up to the auxiliary input and started poking around with the O-scope. Left channel curve looks good. Right channel curve is very distorted at the outputs. Now I am working on following that back through the audio circuit to see if I can isolate the component that is causing the problems.

Also, cleaning everything definitely helped but still have odd crackles when I touch different switches. One thing I noticed is when I rotate the component I get a buzzing out of the speakers. Shake the unit gently and it goes away. I suspect I have something loose.
 
Typical "A" Ganger. Just hit it with a bigger hammer! LOL.

Could be a solder blob rattling around(take off both covers top and bottom, shake a bit), or a cold solder joint on a ground or a wire that's been over-bent and hangin on by a thread. Solid core wire doesn't have the flexibility of stranded, so be careful of sharp bends. Tighten down all boards snug. Don't force the point on snugness. Use locktite if screws keep backing out.
 
Yes, definitely needs the calibrated hammer technique. This little unit is going to be a PITA to fix but it is the cheapest of the ones I own so I am going to start my learning on it. Going to get me a wood stick so I can start poking around on the wires to hopefully find the problem. I also need to inspect the boards for any blown resistors. Saw one of these with a similar oscilliscope image and it was a blow resistor on one of the boards.
 
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