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Galaxy 2100 frequency counter problem

Brandon7861 when I get home from work I will get the main board number. Nomad, the board is untouched. Ive owned my 2100 for at least a decade or two. I am ordering another TD6102 that the vco feeds. Amazing its still available. Ive noticed other schematics show the TA7310 getting the vco feed, but not the board I have. Thanks for all the help guys.
 
You must have some in-between version of the counter board. The only schematic I can find that uses the 10.6975MHz crystal also uses the 7310 mixer (the secret CB schematic). The schematics that show the 6102 mixer have a 3MHz crystal.
 
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brandon7861 said:
You must have some in-between version of the counter board. The only schematic I can find that uses the 10.6975MHz crystal also uses the 7310 mixer (the secret CB schematic). The schematics that show the 6102 mixer have a 3MHz crystal.
Click to expand...
The schematic in the service manual I posted agrees with you and so does the counter board that I have sitting on my desk.
 
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Brandon7861, very sorry. You are correct. The crystals are 3.2768 mhz AND 2.68375 mhz. Normally I use my sniffer loop, 3 turns of wire, coax center to shield, connected to an all band receiver, this case a TS-690S. Normally dialing up the crystals freq you can see on the s meter there's an oscillation. I pick up the 3.2768 crystal. The 2.68375 is iffy (meaning not a solid reading)for the freq counter is doing an oscillation itself. You can also hear this thru the radio speaker, like a two tone generator. This started when I replaced the zener with the 7805 regulator. Tweaking the 2.68375 trimmer did nothing. T602 and T601 did not help either. Not having a replacement crystal, I just loosely injected the 2.68375 mhz signal with the 690 (putting the 690 in transmit, AM, with power control turned down). Parameters changed somewhat, but nothing stable or fixed. This is where I am right now.
 
Any chance the counter's metal case is touching the radio's chassis metal? The fiber washer between the module and the mounting surface serves to keep the two grounds separate. So does the plastic mount screw.

Connecting the two separate ground circuits can cause some noises.

73
 
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No. Metal box is isolated. You said you've mounted the 7805 in the old zener holes. I drilled a small hole in the middle of the two holes for its a ground trace on the bottom side. Grounded the regulator there. You said you used a wire. Sounds like maybe you grounded the regulator somewhere else. Maybe I need to try another ground section, could be introducing unwanted ground currents? I build my own vacuum tube guitar amplifiers and sometimes also have to try different areas to ground it because of noise.
 
I read the other day, on the web, someone showed how to cure hum on his Galaxy freq counter. Basically a .1 or .01 from one of the pins on the main IC to ground. We've all seen this before. I don't recall what pin it was, but I just took a 0.1 from ground and probed the pins til the osc stopped. Rx and tx still good so I didn't kill any IC operations (I hope). Well, for grins I returned T601 and T602, and the counter started to work. I came in the house to post, but going back out to the radio room, it went bad again. I probed around more, touched up on soldering, but nothing. Then, the display now reads 54.000 and that's it. Frustrated.......
 
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I think I figured out how this bugger works.

IC608 is a divide by 2^14, so with 3.2768MHz in, we get 200Hz out of pin 3.

IC606 has two dividers chained together and its function is to divide that 200Hz by 16 (outputting 12.5Hz on pin 6), and by 80 (outputting 2.5Hz on pin 3).

IC603 is a hex gate (4 inverters, a nor, and a nand) and it took modeling to figure this one out. Its function is three-fold. 1-the NAND and one inverter combine the 12.5Hz and 2.5Hz signals to produce a 40ms reset pulse that occurs at a rate of 12.5Hz (skipping one cycle for every 5 cycles of the 12.5kHz inputs). 2-the loop with the inverter-two resistors-diode-inverter is a pulse-shaping network that turns a 40ms high pulse into a very fast transfer pulse. 3-the nor gate combines the signal from IC605 and the 12.5Hz signal to produce a gated version of IC605's signal effectively reducing its duty cycle to 50%. I will come back to this.

IC604 is the input prescaler and divides the VCO by 4, so on ch19, 16.49MHz in produces 4.1225MHz out and sends it to the mixer IC607

IC607 mixes this 4.1225 MHz signal with the 2.67375MHz signal to produce the sum of 6.796250MHz.

IC605 takes this 6.796250MHz and divides it by 10 to produce 679.625kHz and sends this to IC603

Now that we are back to IC603, what happens when you take a 679.625kHz signal and pass it through a 40ms gate? only 27185 counts come through :)

The counter IC will transfer the count to the multiplexer on the rising edge of transfer and latches the display to that number when transfer goes low. For 4 of the 5 transfer pulses, a reset is sent with transfer, but for that one instance where transfer is not followed by a reset, that value is sent to the display driver IC601 (a BCD to LCD converter)

Here is the circuit I made in circuitlab simulating IC606 and IC603 and the resulting waveforms. Note that the 679.625kHz signal was replaced by 10k for the sole purpose of faster modeling because circuitlab is slow as molasses with time bases required for RF analysis. The change has no effect on the illustration.

I do not know if I got this right but I doubt there exists too many wrong ways that produce the right result. IDK.
1782956304943.png
 
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