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crystal replacement alternative in wireless mic?

I recently pick up a Radio Shack wireless mic at Goodwill for $1. I could hear something in the receiver ratting, so I figured it wouldn't work. I was right. It turns out that the receiver has two crystals:

10.245 Mhz and 39.190 Mhz. The 39.190 Mhz crystal was cleanly broken away from the PCB and making the rattling when moved. Problem is that the break was so close to the case that there's nothing left to solder to, so I need a new crystal. I see one on the "bay" but about $10 by the time shipping and tax are added, which sort of defeats the purpose of a bargain. So, what about this crystal instead?

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Most likely the native crystal was working from a fundamental overtone anyway. The frequency of the above one gets me close to the frequency needed, but not quite. Assuming this crystal would even work, would a series trimmer cap allow me to adjust to the proper frequency?

Thank you.

Reply to
-faver-
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Le 23/01/2022 à 18:01, -faver- a écrit :

Worth a try IMHO. Think also on the possibility of slightly modifying the 10.245 or the transmitter oscillator.

Reply to
bilou

Wish there was a schematic somewhere for these. The units themselves are all over the net for sale. Doesn't look like they are the best performers.

Reply to
-faver-

===============

** So the mic is on 49 MHz - right ?

The crystal is an SMD type that just * fell* off the PCB ??? Please explain.

.... Phil

Reply to
Phil Allison

Yes, 49 Mhz system. The crystal housing is HC-49/U. No, it didn't fall, it looks to me like the leads corroded away right at the PCB. The old yellowed glue is left behind with the imprint of where the crystal was. I've read how corrosive some of these glues could be and I think that's what destroyed the crystal leads.

Reply to
-faver-

-faver- wrote: ===========

** Absolutely !

Seen the exact thing, many times - in powered loudspeakers made by dB Technologies. Damn "yellow peril" glue !

4MHz crystals in the DSP system * corroded * right off the PCB and the whole thing stops.

Do you have a matching receiver for 49.xxx MHz ?

IMO you repair idea sounds unlikely to work out - crystal oscillators are fussy and those models are narrow band, about 25kHz IIRC. Mics on higher bands like 175MHz are often 250KHz wide.

FM wireless mics are non simple, but fun to fix.

.... Phil

Reply to
Phil Allison

Well, I do have a radio scanner. That's how I knew that the transmitter at least was working. It seems to be on frequency although, consistent with the reputation I read about these units, the audio frequency range leaves a lot to be desired.

I absolutely hate that glue! I have a transceiver that stopped working. On one of the daughter boards inside the unit, most of the electrolytics were glued down with the stuff. I've been in the process of recapping it because about half of the electrolytics are no longer any good.

So you don't think using the overtone of the crystal I mentioned will serve as a working substitute for the broken off one?

Reply to
-faver-

--------------------- <

** As do I, very handy for such work Long as it can do wide FM up to 1GHz.
** OK, you tricked me with your heading. FYI:

A "wireless mic" is a * MICROPHONE * not a receiver. Plus a crystal is way more likely to come to grief in a MIC !

** Me too, been fighting it for decades.

Criminal that many makers keep on using the vile stuff. Roland, Yamaha, Alesis, dB Tech, Rockit and host of others.

** Maybe worth a go.

But the narrow FM may be your downfall if the frequency is off by even 10kHz.

..... Phil

Reply to
Phil Allison

Hi there,

It's your lucky day. I just looked through my vast and powerful junk collection and I have a crystal marked 39.160MHz. If you think it is close enough, send me an e-mail with a US mailing address and I'll send it to you for free. It is a pull from who-knows-what, and I do not assure you that it is good. 5/32 thick, 13/32 wide, 17/23 tall. Leads long enough to make it through a PC board.

Regards, Tim

Reply to
Tim Schwartz

Thanks, but I don't think this will work. The native crystal was a

39.190 Mhz, so even with varactors or trimmer caps, I'd never be able to get it to the frequency needed. So, unless you had a 39.190.....

Appreciate this, however!

Reply to
-faver-

Bearing in mind that the thing cost you $1, you could try scraping away at the glass around what is left of the crystal pin, to expose as much metal as you can on the wire, and then joining on a fine strand of wire with silver conductive paint (for example the type used to repair car window de-misters). Once you have a good electrical connection, you can cover the joint with 2-part epoxy (araldite etc.) to make it robust.

It is also possible to remove crystals from their metal can, it may still work if you are careful and there will be much more wire to make contact to inside the can.

If you think the thing is worth much more than $1, you can either order a custom crystal or use a PLL frequency sythesiser chip like the ones from Silabs that radio amateurs often use as a local oscillator - they are very simple to use and can produce whatever frequency you need. The frequency can be programmed with some arduino-type processor etc.

Reply to
Chris Jones

I was thinking the same thing. When I was a tech we used silver, and gold conductive epoxy to attach surface mount components. Once cured it was quite strong.

Reply to
Mike S

I like Creative Materials 125-15 conductive ink, but I can't recommend it for this situation because the minimum order quantity is much too large, and it has to be shipped and stored refrigerated, which makes the freight expensive. It also needs to be cured at high temperature to make it conductive (80 degress C will do but hotter is better). It isn't mechanically strong at all, but it is very conductive and in practice has a long shelf life if kept refrigerated, and is a one-part ink so I can dispense small quantities with little waste.

For this job, the stuff for fixing windscreen de-misters ought to do and is more widely available.

I think the carbon-based ink (Bare Conductive etc.) would not do for a crystal oscillator, the resistance would be too high and it would hurt the Q.

Reply to
Chris Jones

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