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Author Topic: Broke 940 Kenwood  (Read 298 times)

WB8PFZ

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Broke 940 Kenwood
« on: June 22, 2022, 06:05:54 AM »

Getting tired of looking at the tape on the 940 that says BROKE. It has the power supply upgrade. All the voltage leds are lit. It basically does nothing. The meter is lit. The sub display is lit. Where to start?
Any help would be appreciated. Mike
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N8YX

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Re: Broke 940 Kenwood
« Reply #1 on: June 22, 2022, 06:22:22 AM »

It basically does nothing. The meter is lit. The sub display is lit. Where to start?
How about the main display - what's going on there?
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K1KP

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Re: Broke 940 Kenwood
« Reply #2 on: June 22, 2022, 06:31:49 AM »

First, check that all the power supply voltages are correct. Next step would be to see if the CPU is up and running - won't get very far without that. Then, work on getting the Main display to work. If you can get that far, then you can start working your way through the TX and RX signal processing blocks.

-Tony, K1KP
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WB8PFZ

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Re: Broke 940 Kenwood
« Reply #3 on: June 22, 2022, 06:51:54 AM »

The main display shows nothing. No audio. Pretty much meter and sub display lights. Sub display shows small rectangle shapes. NNNNNNNNNNN
                                             NNNNNNNNNNN
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WB8PFZ

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Re: Broke 940 Kenwood
« Reply #4 on: June 22, 2022, 06:52:58 AM »

How would I know if the CPU is running?
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N8YX

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Re: Broke 940 Kenwood
« Reply #5 on: June 22, 2022, 07:02:07 AM »

Question:

Did the rig ever work, or was it acquired in a non-operative state?

I would start with the Digital (A and C) Boards. Someone's fingers may have been into the thing before it came into your possession. Verify all cabling to those boards.

What do you have in the way of test gear?
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WB8PFZ

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Re: Broke 940 Kenwood
« Reply #6 on: June 22, 2022, 07:13:48 AM »

It worked fine. I turned it on one day and it did crazy never before seen things. Did the A=B thing a few times and it would worked until turning it off would start the crazy process over again. I have a good collection of test equipment.
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WA1YIH

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Re: Broke 940 Kenwood
« Reply #7 on: June 22, 2022, 07:27:42 AM »

What I would check is the CPU oscillator crystal next. A friend of mine found a 940 dead and that’s what it was. Just a suggestion. 
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N8YX

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Re: Broke 940 Kenwood
« Reply #8 on: June 22, 2022, 11:20:11 AM »

What I would check is the CPU oscillator crystal next. A friend of mine found a 940 dead and that’s what it was. Just a suggestion.
Good suggestion - the CPU drives all sorts of things in these rigs.
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ZL4AI

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Re: Broke 940 Kenwood
« Reply #9 on: June 22, 2022, 11:50:28 AM »

Try reading the TS-940 page which was written with the focus of fixing the 940. Explains the process of working from power supply through to other parts of the circuit. TS-940 page can be located from

https://www.qrz.com/db/ZL4AI
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WB8PFZ

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Re: Broke 940 Kenwood
« Reply #10 on: June 22, 2022, 01:47:11 PM »

ZL4AI , WA1YIH thanks for the info. Mike
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WA4ZYN

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Re: Broke 940 Kenwood
« Reply #11 on: July 02, 2022, 08:49:44 AM »

The main display shows nothing. No audio. Pretty much meter and sub display lights. Sub display shows small rectangle shapes. NNNNNNNNNNN
                                             NNNNNNNNNNN
[/quote]

Hello! Just to clarify:  when you say "display shows nothing", does it possibly mean it shows "dots"?  Or just totally blank?  Dots would mean PLL unlock, which would give you no audio, no transmit.  The rectangles on the subdisplay might indicate that the subdisplay needs a "reset", or even battery replacement.  Perhaps even same for digital board battery(?).

Just thinking of my own 940 fun times I've had.

Good luck.  Wishing you the best.
73,
Francis WA4ZYN
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WB8PFZ

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Re: Broke 940 Kenwood
« Reply #12 on: July 02, 2022, 12:11:37 PM »

No dots. With the warm weather spending time with the grand kids. This may be a winter project. Just trying to get some ideas. Thanks all and Happy 4th. Mike
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VE3TMT

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Re: Broke 940 Kenwood
« Reply #13 on: August 22, 2022, 12:03:03 PM »

My 940 would all of a sudden break out into a crazy squealing sound and the display would flash all kinds of gibberish. Leave it for a while and all was fine and then it would do it again.

My issue turned out to be with the large IC that is mounted on the digital board under the speaker. I believe it was IC20 on the Digital A unit.

It was not seated tightly in the socket. I fixed it by reflowing all the pins on the socket and tinning each IC pin as well. This added just the correct amount of thickness to the pins to seat it tightly in the socket. I never had the problem again.
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