eHam

eHam Forums => Mods And Repairs => Topic started by: WB8PFZ on February 16, 2023, 10:37:31 AM

Title: Broke Torrestronics TK-1 readout
Post by: WB8PFZ on February 16, 2023, 10:37:31 AM
My digital readout was working fine on my Drake R4C. I turned it on and the display reads 354.8 and does not change . Unplugging the rf input does not change the readout. Any users of these? Thanks Mike
Title: Re: Broke Torrestronics TK-1 readout
Post by: K4JJL on February 21, 2023, 06:24:25 AM
Is anything coming out of cable you're plugging into RF input? 
Title: Re: Broke Torrestronics TK-1 readout
Post by: WB8PFZ on February 21, 2023, 01:04:29 PM
Yes, I can read the frequency on my frequency counter just fine coming out of the radio. What's odd is that no matter what I do the readout never changes on the Torrestronics box.
Title: Re: Broke Torrestronics TK-1 readout
Post by: N7EKU on February 21, 2023, 04:23:54 PM
Hi,

It looks like this was originally a kit, so the manual gives lots of testing and adjusting help.

I noted that it looks like all the IC's are using sockets.  I would carefully remove each one and then re-seat it in its socket as the contacts can become oxidized over time.  I would also add some deoxit to any mechanical switches used.

The kit didn't look to be using any tantalum caps which would for sure be suspect, but you could check the electrolytic ones used either by sight for leaking, or with an ESR meter.

73
Title: Re: Broke Torrestronics TK-1 readout
Post by: WB8PFZ on February 21, 2023, 06:56:17 PM
What seems odd is it worked fine one day and the next it didn't. The only switches are simple toggle switches and the inside looks perfect not like it was not taken care of. I am thinking the drivers for the readouts.
Title: Re: Broke Torrestronics TK-1 readout
Post by: WB8PFZ on February 21, 2023, 07:01:29 PM
2 electrolytics in the power supply and I have power. The frequency of the oscillator is correct. All the ics are in sockets except for the display drivers..
Title: Re: Broke Torrestronics TK-1 readout
Post by: WB8PFZ on February 22, 2023, 04:06:19 AM
I removed all the SN74LS190N from there sockets and the display went blank. I would think this is telling me the drivers are ok and the problem is in front of that part. If I install the 190's back into there socket what ever number was on the display returns no matter what chip I reinstall.
Title: Re: Broke Torrestronics TK-1 readout
Post by: K4JJL on February 22, 2023, 06:31:52 AM
Sounds like one of the 74LS190 chips died and it's not counting or resetting.  Do you have an oscilloscope?  If so, probe each chip's pin 14.  That's the clock pulse input.  They're cascaded such that the ripple clock output (pin 13) is connected to the clock input (pin 14) of the next chip.  As you go down the chain of clock inputs and ripple outputs, the frequency will keep dropping (as it divides inside each chip).

It's also possible that the dip switch contacts are crusty and the counting presets are being steered way off.  In that case, try some DeOxit and flip them back and forth.
Title: Re: Broke Torrestronics TK-1 readout
Post by: W9IQ on February 22, 2023, 06:41:09 AM
Have you checked TP1 and TP2 to ensure the correct clock frequencies are present? Also check the emitter of Q2 to see if your input frequency is present and is approximately 5 volts in amplitude.

- Glenn W9IQ
Title: Re: Broke Torrestronics TK-1 readout
Post by: WB8PFZ on February 22, 2023, 07:21:25 AM
Thanks for the info. I have checked TP1 and it is spot on frequency. Will explore the other checks. Thanks again.
Title: Re: Broke Torrestronics TK-1 readout
Post by: WB8PFZ on March 03, 2023, 12:33:55 PM
Going thru the manual and see that the display is reading the offset frequency. Next to check and see if the preamp circuit is working, a few transistors.
Title: Re: Broke Torrestronics TK-1 readout
Post by: WB8PFZ on March 04, 2023, 08:05:24 AM
After checking the transistors in the preamp section I have found that the first transistor has a base to emitter short. Have one on order. Will report back when repaired. Thanks to all. Mike
Title: Re: Broke Torrestronics TK-1 readout
Post by: WB8PFZ on March 08, 2023, 07:58:43 AM
Replaced the preamp transistor a 2N918 and all good. Thanks all. Mike