Strange question, Wax on circuit board

amplifiers, receivers and loudspeakers
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mrow2
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Strange question, Wax on circuit board

Post by mrow2 » 13 Apr 2013 02:07

Have not ever seen this before. I clean up, do light restoration mostly cleaning and beautifying, vacuuming etc for vintage TTs and Receivers, Amps. Found an optimus STA-300 receiver, neat little thing nice bookshelf type sound. Opened it for cleaning and vacuuming, R rear section of board had 1/16 inch or more of soft wax all over it, mostly around what might be the tuner section. Thinking someone had burnt a candle at some point on top of the unit, friend and I removed all the wax by scraping and dabbing it off. Some residue remains between components. After we removed it, got to thinking it was intentional that it be there, not like candle wax really and the odor had an electronics smell to it. What would be the purpose of this, have not seen it on any board covering just a portion of a board before. Components included ICs, transistors, resistors, tuning cans, caps, diodes, etc. I can pack the wax back on it if necessary. It sounded ok when powered it up. Anyone know what this is and does it really matter? I don't think it surrounded any ICs. I tested the tuner and the preamp. Didn't think to make a pic of the board, but roughly a 2x3 inch area of the main board was covered fairly neatly.
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Optimus STA-300 Receivr cc.jpg
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JaS
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Re: Strange question, Wax on circuit board

Post by JaS » 13 Apr 2013 07:55

I can only think it's some sort of potting compound? I'm not sure why it would be used in this application though :-k

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JaS

geoffcb
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Re: Strange question, Wax on circuit board

Post by geoffcb » 13 Apr 2013 08:41

JaS wrote:I can only think it's some sort of potting compound? I'm not sure why it would be used in this application though :-k

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JaS
Yes, sometimes wax is used on trimmers after alignment. Maybe they used the wax for "tropic proofing" for use in humid climates? Spray lacquer is often used for this.

cats squirrel
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Re: Strange question, Wax on circuit board

Post by cats squirrel » 13 Apr 2013 10:38

any battery cells around? The battery in the Quad FM4 can spew its guts all over the pcb. Other possibilities include capacitor contents.

mrow2
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Re: Strange question, Wax on circuit board

Post by mrow2 » 14 Apr 2013 02:12

It's at friend's house now, cannot check it but I believe we did not see any batteries. The wax was only 3/32 inch deep, not going into tuning cans. There are two small coils, those had cloth inside them, saturated with the same wax. We left those in them. Tightly fitted resistors and transistors still have some around the connections. What I seem to be hearing is that removing the soft wax as we did does not seem to threaten the unit's performance but I still don't know why it was there. I could probably put 75% of it back if there's a reason to.

I did not examine the FM real closely and it doesn't have an AM antenna but a few FM stations we are familiar with tuned in fine. The wax was some distance away from the amp section and heat sink so it doesn't get hot. We initially tried a hair dryer on it to run it off with the unit standing sideways but I didn't allow it to get too close to the board, parts never too hot to touch, maybe 110F perhaps. The wax was happy. Guess it's amazing we didn't kill it, huh? Ten dollars was at risk.

davidsrsb
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Re: Strange question, Wax on circuit board

Post by davidsrsb » 15 Apr 2013 10:48

Wax could have been applied as damping. FM radios are very microphonic

mrow2
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Re: Strange question, Wax on circuit board

Post by mrow2 » 15 Apr 2013 18:27

OK, maybe during QC testing they realized this and added the wax-fix in production. Now, I've scraped most of the jacket off the microphone, hope it's not too sensitive to feedback!

TWTRTECH
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Re: Strange question, Wax on circuit board

Post by TWTRTECH » 21 Apr 2013 03:24

The purpose of using this beeswax is twofold. First, to keep the parts like tuning slugs from moving around over time... and second, to keep the parts from being microphonic in the tuner circuit. It should be left alone unless a part is being replaced.

CollXdoh
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Re: Strange question, Wax on circuit board

Post by CollXdoh » 18 Oct 2019 15:57

So,help me!!!Iv seen this before & recall I'd attempted too clean such up myself but then radio never recovered too function. Iv just found new old Maxcom 4E tried powering but failed as no proper leads &ic,decided too look inside as Super and Midland boards etc, & there next vr as if it's boiled over its like a pool of wax Enshrouding many components!! What too be done here? I'll get a photo up & im not sure if such is slop or reaction or whatsoever?!

CollXdoh
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Re: Strange question, Wax on circuit board

Post by CollXdoh » 18 Oct 2019 16:01

Here is the Maxcom 4E wax pool in question!
image.jpeg
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kalaur
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Re: Strange question, Wax on circuit board

Post by kalaur » 19 Oct 2019 20:13

IMO, unless there is a component you know needs to be replaced in there, just leave it alone.

CollXdoh
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Re: Strange question, Wax on circuit board

Post by CollXdoh » 20 Oct 2019 14:22

Iv only just inherited it from a shop that pat test before sales etc,but haven't tried it. I think,as climate maybe assembled elsewhere certain spray for quartz cans etc ,but then Iv seen this occur in valve sets, I recall 2sets of possible notions but not exact reason. You would think as wax depth covers components heating would ensue??!

davidsrsb
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Re: Strange question, Wax on circuit board

Post by davidsrsb » 21 Oct 2019 02:54

Do not disturb it, you risk messing up the RF alignment

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