Nady 101 VHF

[upicman]

I just picked up a Nady 101 VHF at a local flea market. The transmitter seems to be outputting RF as indicated on the spectrum analyzer. The TX led on the receiver never illuminates. I was hoping someone might have a schematic. The crystals are the same frequency in both ends, but I get no audio out when the guitar is plugged in.

Suggestions for alignment? Schematics?

Thanks,
Rick

[stj]

Re: Nady 101 VHF

start with foto's and check the cable on the transmitter for breaks.

[upicman]

Re: Nady 101 VHF

I have verified continuity from ring and tip to the respective points on the circuit board. I am not sure what you are looking for with regards to pictures, so I quickly snapped a couple. If you have a more specific area, please let me know.

Thank you for your quick response.

[stj]

Re: Nady 101 VHF

did you check for shorts between the ring & tip?

[upicman]

Re: Nady 101 VHF

Yes.

[stj]

Re: Nady 101 VHF

o.k.
do you know the frequency and if it uses AM or FM ?
i'm thinking it would be usefull to see if the transmitter is transmitting.
btw, i dont suppose you have a link to a manual?

[upicman]

Re: Nady 101 VHF

Crystals read 170.225. I actually have a spectrum analyzer. It shows carrier, but I don't see modulation with 1 khz input, so I can't really tell if it's AM or FM.

The manual I snagged was for operation of a similar device, but with no schematics or alignment prcedures. The LED on the transmitter is only to indicate power. It flashes when I turn the slide switch on. If I put a weak battery in, it comes on and stays on, indicating battery replacement is required. (According to the manual)

I'll have to drag out the scope and start tracing the input and see if it gets past the compander (NE571). Any other suggestions would be appreciated. I don't want to touch teh rf transformers because I don't thiink the problem is there, and I wouldn't want to literally screw things up unnecessarilly.

Thanks for your advice.

Rick

[stj]

Re: Nady 101 VHF

170mhz is in range of most 2m ham radio's
you may find someone who can tune into it for you.

otherwise, you need to try to find the mixer that modulates the input with the oscillator.

i wont sugercoat this, i hate analog radio repair.
dont touch any controls or related capacitors.
and dont bend or move any coils.

the good thing - although not in this case,
is that with modern digital technology that transmitter could probably be done with a couple of logic chips and a coil - not much more.

[upicman]

Re: Nady 101 VHF

Okay, I guess I didn't have the signal generator output high enough. My VX-7R can hear the transmitter. The guitar comes through. I guess I need to concentrate my efforts on the receiver. That'll mean the scope. I won't be able to get to that tonight.

You have moved me along. Thanks for the guidance so far. I'll get this thing working sooner or later.

Rick

[upicman]

Re: Nady 101 VHF

Boy do I feel silly. With all the stuff I have, I didn't think of using the handy-talky to troubleshoot. Thanks for the lesson!

Rick

[stj]

Re: Nady 101 VHF

if you can pick it up on the yaesu then it must be FM.
that's handy, you can use the yaesu as a signal source as it belts out atleast 3w on full power.

amazing luck/coincidence you had a HT

[stj]

Re: Nady 101 VHF

hey, how about you bin the reciever and buy a BaoFeng UV-3r for $20

[upicman]

Re: Nady 101 VHF

It won't let me transmit in that band. TV. But if the guitar transmitter is known to work (which it is now), I can start poking around the receiver as soon as I get a chance.

I'm feeling better about this now. Thanks again.

[upicman]

Re: Nady 101 VHF

hey, how about you bin the reciever and buy a BaoFeng UV-3r for $20

I don't know how it would go with the guitar amp decor

...but it could provide some interesting distortion!!

[upicman]

Re: Nady 101 VHF

Okay, I've found the problem, but I don't know how to fix it easily. The crystal is shorted. Does anyone have any suggestions as to how to clear a short from a crystal? It's a 170.225 MHz in an HC-49UX case.

**** Update during the writing of this:**********

I went to get an accurate resistance reading of the crystal and noticed that it was rising from 74 ohms to about 80 ohms as I was holding it. I put clip leads on and proceeded to heat it with a lighter. After a couple of short applications of direct flame on the case, the short cleared! I reinstalled the crystal in the receiver and I am now playing wireless!

Many thanks to STJ for his patience and guidance. Once I knew which tree to bark up, I poked around the receiver and discovered the crystal oscillator wasn't (oscillating). I suspected the driving transistor at first (as it would be easy to substitute) but was disappointed when it tested okay. Removing the crystal led me to the beginning of this post.

I am now a happy camper. The wireless guitar system cost me $1 at the flea market, but that pales in comparison to the fun I had fixing the unit.

Thanks also to badcaps.net, which I discovered when I found schematics for the two VIZ lab power supplies I still need to fix. I'm now a big fan.

Rick

[stj]

Re: Nady 101 VHF

it's probably leaning over in the can and may not last.
you should keep an eye out for a new crystal.

[upicman]

Re: Nady 101 VHF

Where would I get one? Sounds like an expensive special order.

[stj]

Re: Nady 101 VHF

good question, i'v never seen a xtal anywhere near that frequency before.
maybe if it dies, use a digital synthesized oscillator.
i bet some chinese seller on ebay has such stuff.

[upicman]

Re: Nady 101 VHF

I measured the receiver's crystal oscillator frequency at 51.130MHz. That, times three, plus the IF gets me to about 170.233MHz, which happens to be what the transmitter was measured at. The 170.225MHz stamped on the cases was just to indicate what the system 'channel' ran at, so a couple of them could be used in the same group of performers with slightly different non-conflicting frequencies.

51.130MHz sounds more reasonable. At least I know what to look for if this one decides to go south again. I suspect the receiver was dropped and caused the fragile crystal holders to shift inside the can. The heating must have moved them away from the side enough to remove the short. I was tempted to unsolder the can and remove the top, but crystals are sealed with nitrogen gas inside. I have a good shop in the basement, but it's not [/I]that[/I] good!

In the meantime I'm rockin' on, cordlessly, thanks to you, stj.

Have a great day,
Rick

[rafik]

Re: Nady 101 VHF

Hello, I am new in this forum but I am ready to share my knowledges or schematics with you.
Sorry, the reason that I am bother you this time is that I need the schematic of the Nady 101 VHF. Please If someone could it share with me it will be great.
Thank you in advance for your attention.

73! rafik