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 Post subject: Kenwood DG-5 Digital Display for TS-520S - Not Working
PostPosted: Jan Mon 11, 2016 3:15 am 
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I acquired a DG-5 with the TS-530S that I just refurbished. The DG-5 is not working. Here is the configuration information, the problem and some diagnostics performed with a Tektronix 2465B oscilloscope:

1. DG-5 plugged into a TS-520S with voltages applied and a valid signal on the TS-520S CAR, VFO and HET lines. The TS-520S is set to the 40M band with frequency on vernier dial set to 7.168 MHz. The vernier dial accurately indicates the receive frequency.

2. If the DG-5 switch is left in the ON position when the TS-520S is powered on, the display will be illuminated. However, if the DG-5 switch is toggled to the OFF and then ON position, the DG-5 appears completely dead. The only way to return the DG-5 to a state with its display illuminated is to disconnect the power leads and wait several minutes before powering up the TS-520S again.

3. DG-5 displays gibberish - 92.394.2 or 04.550.1 arbitrarily when its switch is left in the ON position and the TS-520S is powered on. The DG-5 displays either one of those invalid frequencies even if the CAR, VFO and HET cables are all disconnected! If the DG-5 is left on long enough, the frequency will eventually toggle between those two frequencies.

4. The following signals were measured at the indicated test points:

TP1 (HET input to Q3) 3.455 MHz at 15mV
TP2 (HET input to Q6) 3.389 MHz at .29V
TP3 (VFO input to Q10) 5.059 MHz at 29mV
TP4 (CAR input to Q13) 15.13 MHz at 73mV
TP5 (CAR circuit D12 at emitter of Q15) Repetitive signal cannot be detected and frequency cannot be determined by scope. Amplitude of wave is 7.3mV
TP6 (Preset counter circuit drain of Q18) Repetitive signal cannot be detected and frequency cannot be determined by scope. Amplitude of wave is 7.3mV
TP7 (Preset counter circuit base of Q19) Repetitive signal cannot be detected and frequency cannot be determined by scope. Amplitude of wave is 7.3mV

TP8 (Reference oscillator circuit emitter of Q21) 9.512 MHz at .370V
TP9 (CAL input to collector of Q23) Repetitive signal cannot be detected and frequency cannot be determined by scope. Amplitude of wave is 7.3mV

The theory of operation very roughly speaking is to subtract the sum of the VFO and CAR from the HET signal to arrive at the display frequency. I did a check for poor solder joints, but did not see any.

I would appreciate any ideas in troubleshooting this unit. Thank you,

Steffen


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 Post subject: Re: Kenwood DG-5 Digital Display for TS-520S - Not Working
PostPosted: Jan Mon 11, 2016 3:31 am 
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Hi Steffen,

If it hasn't been done already you will need to follow the factory service bulletin for the plate through joints. They will appear OK visually but many will not be OK electrically and the only reasonable approach if you want a reliable DG-5 is to go through the entire factory update. It is available here: http://www.qsl.net/bg4aaf/book/kenpic/kenwood.htm

I have done the same process to my DG-5 and the built in display units in my TS-820 and R-820. The full service manual is also available on the web if you don't have a copy already but do the bulletin first.

Good luck, it is tedious.

Rodger WQ9E


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 Post subject: Re: Kenwood DG-5 Digital Display for TS-520S - Not Working
PostPosted: Jan Mon 11, 2016 3:43 am 
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Thank you Rodger. I will work through this and really hope it is indeed the problem. I will need a few days to report back. 73.


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 Post subject: Re: Kenwood DG-5 Digital Display for TS-520S - Not Working
PostPosted: Jan Tue 12, 2016 3:30 am 
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I may just give up on this one. I read the service manual thoroughly and the factory service bulletins. However, two things really frustrate me- 1) The service manual that is on the web is a poor res scan and the counter board pictorial diagram is far to blurry to be able to locate components from the underside of the board. You have to test voltages from the underside because the top is too densely packed with components and the component leads are insulated in the case of resistors. 2) I still don't see where the plate through joints are located on the board. I'm surprised that Kenwood made such a poor quality board in the first place.


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 Post subject: Re: Kenwood DG-5 Digital Display for TS-520S - Not Working
PostPosted: Jan Tue 12, 2016 3:25 pm 
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I should mention that the counter board has several wire jumpers soldered to ICs as well as between discrete components and the metal frame. I would have preferred to troubleshoot this board without former invasive "fixes". However, it is teaching me a lot despite my frustration. I measured supply voltages to the analog and logic circuits. The supply lines are at 8.6, 4.3 and 4.5 volts. A voltage difference of 0.5 volts on the 5V line I would imagine being acceptable. At any rate, if you can give me a clue inasfar as identifying the plate throughs, I will delve further. Also, if there is a better res service manual, I can measure bias voltages. I see that my signal voltages at the test points are all low. If the plate throughs do not resolve the issue, then I will proceed with tracing out the low amp gain.

By the way, I figured out why the display always shows a bogus frequency. It's because there is an internal switch to turn off blanking pulses. The blanking is used to deactivate the display if there is excessive noise or disconnected cables. The internal switch is useful during troubleshooting.


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 Post subject: Re: Kenwood DG-5 Digital Display for TS-520S - Not Working
PostPosted: Jan Tue 12, 2016 4:08 pm 
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Steffen,

I don't have a DG-5 apart now but the way to identify the plate through holes which connect the traces on opposite sides of the board is they are the holes with no component lead passing through. The repair is to place a lead through them and solder each side to provide a good connection.

Do you have the full #54 service bulletin from Kenwood? Page 2 provides the specific locations for all 84 plated through holes, 2 on the display board and 82 on the main board. It is available here: http://www.radiomods.co.nz/kenwood/kenwooddg5.html

Identify a couple of these holes and the holes between the group of 5 rows of ICs and the set of ICs perpendicular to these are easy to find in the open area between these groups of ICs. If those already have leads through them then someone had done at least part of the process and perhaps all of it.

Rodger WQ9E


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 Post subject: Re: Kenwood DG-5 Digital Display for TS-520S - Not Working
PostPosted: Jan Tue 12, 2016 4:30 pm 
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Joined: Feb Tue 07, 2012 9:32 pm
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Location: Middlesex,NJ
HI STEFFEN:

THIS THE SHARPEST SERVICE MANUAL I CAN FIND OTHER THAN AN ORIGINAL
PRINT THE BOARDS IN COLOR.

http://www.kg6haf.com/downloads/DG5_Service.pdf

LET ME KNOW.

WALTER-W2WIQ


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 Post subject: Re: Kenwood DG-5 Digital Display for TS-520S - Not Working
PostPosted: Jan Wed 13, 2016 2:06 am 
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Thank you Walter and Rodger. I examined the DG-5 with the modification notes. It seems the previous owner performed the plate throughs and other recommended mods. Actually, the board looks a bit hacked. I may put my energies into building a DG-5 emulator instead. Let's see.


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 Post subject: Re: Kenwood DG-5 Digital Display for TS-520S - Not Working
PostPosted: Jan Sat 16, 2016 11:01 pm 
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I ordered the parts needed to build the DG-5 emulator. However, after thinking more about Rodger and Walter's advice along with an additional email from Walter, I thought of the Duke and decided to keep working on the original DG-5 unit. Here is what the Duke said:

Attachment:
wayne_small_new.jpg
wayne_small_new.jpg [ 21.96 KiB | Viewed 3579 times ]


Wouldn't you keep going too?

At any rate, I removed the mounting screws from the main counter board and then retightened and resoldered. Now, the unit displays a frequency that does indeed change with rotation of the TS-520S tuning knob! The frequency displayed does not do the calculation of HET - (VFO + CAR), but this is indeed enticing improvement. I will continue.


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 Post subject: Re: Kenwood DG-5 Digital Display for TS-520S - Not Working
PostPosted: Jan Sun 17, 2016 12:18 am 
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Steffen,

If you are anything like me repairs I have started are impossible to ignore. Sticking with it will result in victory.

When I was going through mine I recall one of the notes on the web stated most of the issues arise in the hetrodyne oscillator input area so you might pay particular attention to that area. As Kenwood states in the service note a heat gun may be useful and that is how I found the problem in my very similar TS-820S display.

Good luck!

Rodger WQ9E


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 Post subject: Re: Kenwood DG-5 Digital Display for TS-520S - Not Working
PostPosted: Jan Sun 17, 2016 3:18 am 
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I resoldered more points on the underside of the board and used a heat gun as well. I see where former repairs damaged the circuit board to some degree. The following frequency discrepancies may be a clue as to the location of the circuit at fault. I set the mechanical dial to 0, and with the unit in CW mode and VFO function, I cycled through the band switch. The left column is the band and frequency on the TS-520S dial, and the right column is the readout on the DG-5.

1.8 - 0.8000
3.5 - 2.5001
7 - 4.9999
14 - 12.9998
21 - 18.9999
28 - 26.9992
28.5 - 26.4991
29.1 - 26.0993


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 Post subject: Re: Kenwood DG-5 Digital Display for TS-520S - Not Working
PostPosted: Jan Sun 17, 2016 3:47 am 
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Joined: Feb Tue 07, 2012 9:32 pm
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Location: Middlesex,NJ
HI STEFFEN:

WITHOUT LOOKING AT THE SCHEMATIC I CAN SEE WE ARE TALKING ABOUT THE 1MHZ IC STAGE.

GO TO PAGE 34 AND THE REFERENCE OSC. SCHEMATIC.THIS IS THE CIRCUIT YOU WANT TO CHECK USEING YOUR FREQ. COUNTER.FROM THE OSC TO Q22 TO IC'S 5 THROUGH 10.THESE ARE THE COUNTER MULTIPLIER AND DIVIDER IC'S.
THE PROBLEM AT THIS POINT IS NOT IN THE RF CIRCUITS.

WALTER-W2WIQ


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 Post subject: Re: Kenwood DG-5 Digital Display for TS-520S - Not Working
PostPosted: Jan Sun 17, 2016 8:33 pm 
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Agreed. I put a frequency counter on the chain of IC5 to IC10 and also put a scope on the signals to view the amplitude. The results were interesting and may indicate a failure of IC10. Please see if you agree:

IC5 pin 14 = 10Mhz @ 190mV
IC5 pin 11 = 1MHz @ 0.395V
-
IC6 pin 14 = 1MHz
IC6 pin 11 = 0.1MHz
-
IC7 pin 14 = 0.1MHz
IC7 pin 11 = 0.01MHz
-
IC8 pin 1 = 0.01MHz
IC8 pin 12 = 0.001MHz
-
IC9 pin 14 = 0.001MHz
IC9 pin 11 = 0.0001MHz
-
IC10 pin 14 = 0.0001MHz
IC10 pin 11 = small or low rep rate signal - unable to be counted or displayed on scope

I want to try to jump IC10 pins 14 and 11 in order to see if I observe a change in the displayed frequency. That would lead me to be almost sure that IC10 is defective and the root of the incorrect display frequency.


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 Post subject: Re: Kenwood DG-5 Digital Display for TS-520S - Not Working
PostPosted: Jan Sun 17, 2016 9:29 pm 
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I jumped IC10 pins 14 and 11 and the frequency does change.


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 Post subject: Re: Kenwood DG-5 Digital Display for TS-520S - Not Working
PostPosted: Jan Tue 19, 2016 2:36 am 
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I need more time to do the calibration. However, I suspect that there may be more than just one problem. Since repairing the ground connection to the frame and getting some signs of life from the unit, I decided to take some measurements once again.

1) I set the TS-520S to CW mode, VFO function and 21MHz band at a frequency of 21.566MHz. I measured the HET signal at the HET jack with an accurate frequency counter. It measured 29.89563. I then set the DG-5 to counter mode and plugged the HET plug into the counter jack. The DG-5 readout displayed 18.8946. This inaccuracy does not have anything to do with the CAR and VFO circuits because the signal goes through the wide-band amp, Schmidt trigger for shaping and then into counter circuitry. This leads me to suspect the counter circuitry and wonder if IC10 not having a signal at pin 11 is significant after all.

2) In display mode, I see that TP4 off the CAR input does indeed have a signal at the correct frequency. There is also a signal at the correct frequency at the base of Q13. However, there is no such signal at the base of Q14. As a result, there is no input from the CAR buffer to the CAR mixer.

3) In display mode, I see a correct VFO signal at TP3, but not into Q10.


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 Post subject: Re: Kenwood DG-5 Digital Display for TS-520S - Not Working
PostPosted: Feb Fri 23, 2018 1:58 am 
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I get the same frequencies you reported in the post in usb/lsb mode. My dg-5 works in cw and tune, but the tracking is off a bit. I'm thinking I need to check calibration.

My question is did you ever repair your dg-5?

Jamie


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 Post subject: Re: Kenwood DG-5 Digital Display for TS-520S - Not Working
PostPosted: Feb Fri 23, 2018 4:13 am 
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I did not repair it successfully because the board just had too many bad traces due to prior repair jobs and troubleshooting. I ended up building an emulator that works perfectly.


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 Post subject: Re: Kenwood DG-5 Digital Display for TS-520S - Not Working
PostPosted: Feb Fri 23, 2018 4:13 am 
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I did not repair it successfully because the board just had too many bad traces due to prior repair jobs and troubleshooting. I ended up building an emulator that works perfectly.


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 Post subject: Re: Kenwood DG-5 Digital Display for TS-520S - Not Working
PostPosted: Jun Sun 17, 2018 6:24 pm 
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Joined: Jun Fri 10, 2011 8:14 pm
Posts: 5
Hi all, recently got a dg-5 for my ts-520s. worked fb on 160 80 and 40 after a few days of use.
some intermittant stuff b4 then.
14 mc's was gibberish so took it out of the case and eyeballed the board, didnt see anything out of
ordinary so blew out the dust and gave it a few shots of contact cleaner to help blow out anything. put
it back in case and 14 mc now working - cool.
15 and 10 finally opened and they dont work correctly at all, so will try the same again.
will also try to loosen and retighten all screws as that had been a good fix on a lot of misbehaving
equipment in the past.
Jim kw3u


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