SX-42 Progress and questions

[W7SOE]

I have made good progress in getting the beast back in order.  I found bad 220k resistors in the audio section that, when replaced, brought to audio back loud and clear.  The HV filter choke was humming and oozing a waxy substance, it has been replaced.  I mentioned the bad output transformer in a previous post.

The 455KHz and 10.7mc IF alignment went well.  Well, only because I skipped the section for adjusting the crystal filter.  I have never quite figured out how to do that right and this one seems to work so I am leaving it alone.

The BFO is dead.  No plate voltage on the 7A4 (or the wire leading to it), the bfo and s-meter amp.  Wafer switch?

Aligned the first two bands which went ok except that I cannot get a peak on C6, the trimmer cap on the antenna transformer.  The signal just grows until It is all the way in.  I am not sure what to look for here.

And now for the real stupidity.  I decided to put deoxit on the bandswitch contacts.  Of course it went other places including on the phenolic wafers.  Now the switch is binding, I have to assume that the phenolic absorbed it and swelled.

I have done this to a WORKING SX-42 BANDSWITCH.  ARRRRRGGGGHHHHH!

I left a heat-lamp on it last night in the hope it would dry up, it seems only a tad better if at all.

This causes me great pain.

Cheers

Rich

[Ralph W3GL]

"DEOXIT"

NEVER, but NEVER spray that stuff on anything!!!

Use a Q-Tip or something like that... Soak and Wipe...

[n2bc]

I spray de-oxit into a tiny bottle - actually a cleaned out model paint bottle.  Dip a toothpick into the de-oxit.  Works great, no flooding the area, no 'shedding' cotton from a Q-tip.

[Chris P.]

For the BFO problem, look at the wafer switch. In CW mode voltage comes from the regulator tube, through that switch to the plate. Mine developed the same problem. Cleaning and tightening the contacts fixed it.

[W7SOE]

For the BFO problem, look at the wafer switch. In CW mode voltage comes from the regulator tube, through that switch to the plate. Mine developed the same problem. Cleaning and tightening the contacts fixed it.

Thanks Chris, that is where I will look.

Man, I had no idea deoxit was such a trap.  I will never spray it again.

Is it a good idea to try to lube wafer switches, where the inner disk meets the outer?

rich

[KM1H]

You should have immediately flushed that crap off with CRC or a similar spray. Just hope that you wont create a conduction path thru the phenolic from the B+ that is on some wafers.  It will do the same to phenolic tube sockets.

DeOxit has caused many otherwise good radios to become parts sets and maybe its time they get a good lawsuit for not having explicit useage instructions.

Ive been using the toothpick and Q Tip for years but imediately flush everything with CRC.

Carl
KM1H

[W7SOE]

I did rinse it off right away with some aerosol contact cleaner. I hope that helps.

Rich

[Rob K2CU]

You might try 90% Isopropal Alcohol for all cleaning. very little water remains.

[KC4VWU]

He's right. 90% or better rubbing alcohol works very well. Whatever you use, make doubly sure it is a non- residual cleaner; highly volitile. Nothing should be left, zero, zilch, nada. Also, never saturate with anything you may use; be sparingly.

If you used somthing that will totally dissipate on the bandswitch, give it a little time to leave the phenolic wafers. I'd let it sit a while and see how that goes before you power it on for long. I think it's still very fixable, but if you get any arc-overs there, that is when trouble begins.

Phil

[W1GFH]

The band switches are Hallicrafters big weak spot. They were poorly made and not intended to last 60 years or more. I had an SX-28 that became a parts rig when 3 or 4 contacts snapped off as a result of cranking it back and forth after a DeOxit bath. Maybe let it cool out over a long week or so. Later you can go over it with a magnifying glass and a dental pick and carefully adjust any contacts that are binding.

[W7SOE]

Thank you all for the advice.  Luckily the bandswitch has freed itself up, I suppose the binding wafer have shrunk some.

I will go in there gently with swaps of rubbing alcohol.

Thanks all for the advice.

rich

[WQ9E]

Rich,

Glad you recovered from the band switch issue!

I have yet to work on an SX-42 or SX-62 that didn't have a leaky mica cap in the discriminator transformer so keep that in mind if the FM doesn't align or work properly.  I have had very few problems with other mica caps but the discriminator units seem to have a problem.  I ran into the same issue with an old Magnavox console equipped with a separate FM tuner chassis; it wouldn't align properly and once again it was a very leaky cap in the discriminator coil.

Maybe I should just stick with the SX-43 since Halli went to a ratio detector in their lower cost model 

Rodger WQ9E

[W7SOE]

Rodger,
    How did you detect the bad mica in the discriminator?  As I recall you peak the top transformer and then look for equal signal drop-off when you vary the signal generator.  If it drops off unevenly from peak then you adjust the bottom transformer.

Mine seemed to peak nicely and the dropoff seemed the same so I left it alone.

I still have the issue where the band one antenna transformer does not peak, it keeps going up until it is screwed all the way in. 

The only thing I can think of is that I am saturating it with my signal generator.

Rich

[WQ9E]

Rich,

My bad mica symptom was very poor response to adjustment of the secondary of the transformer during alignment and poor FM detection on stations.  When operating properly you will find there are three close tuning positions where each FM station is received; it will operate as a slope detector on either side of proper tuning but it should provide good FM detection when centered on the FM frequency if it is operating properly.

Your SX-42 sounds like it is working properly.

On band 1 (AM broadcast band) isn't there a ferrite core in the coil plus a trimmer cap across the secondary on this band?  I don't have a diagram handy but there may also be a fixed padder on some bands so check and make sure it is there if it is called for on the schematic.  A lot of "interesting" things have happened to a lot of radios over the years!

Rodger WQ9E