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Old 15th Feb 2023, 8:20 am   #101
3pinplug
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Default Re: Help needed with - Racal Dana 9081

Hi Paula
Pins 3 and 13 of IC25 are 0v.

I have triple checked and the pin with the dry joint was IC21 pin 15, i have redone the joint but no change as far as i can see. I did this before the above checks. Will be quiet now for a few days until the replacement IC arrives and i fit it, I have so much crossed it sorts it, if i move i may fall over!
Regards
Mark
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Old 16th Feb 2023, 8:08 pm   #102
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Default Re: Help needed with - Racal Dana 9081

I have just finished changing IC25, being soldered top and bottom of board meant the holes the legs of the IC Were in were filled full of solder, a good tip - when i got the IC out there was still solder in the holes preventing the fitting of the new one, i used a pin with a plastic head to hold, put it in or on the hole, touched the soldering iron to the side of the pin and eventually the pin went through the hole and removed the offending solder.
Well now the bad news - fitted new IC and unit still the same, i have another IC so will remove that one and try a second. Have also ordered replacements for Q6 and Q7 as those TP,s were not working, now wheres that pin!!!
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Old 16th Feb 2023, 8:41 pm   #103
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Default Re: Help needed with - Racal Dana 9081

Bit late, but in such situations I would have used a socket.(Mark says "smart***e"!)
Doesn't look original, but saves a lot of messing about and possible pad/ track damage.
This is assuming you have some to hand?
I have such a large quantity of components here it is rare I can't find what I want.
Rob
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Old 16th Feb 2023, 9:29 pm   #104
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Default Re: Help needed with - Racal Dana 9081

Hi Robinshack
It should come out easier this time and yes will definitely fit a socket this time, wasnt expecting it to have to come out again, but iíll be an IC change wizard at this rate!! 👍😂
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Old 16th Feb 2023, 10:17 pm   #105
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Default Re: Help needed with - Racal Dana 9081

Ok Mark. Fingers burned, lesson learned!
I just made that up. Must get a life!
Wishing you luck, you can't be far from the correct result, surely.
Rob
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Old 17th Feb 2023, 11:34 am   #106
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Default Re: Help needed with - Racal Dana 9081

Quote:
Originally Posted by 3pinplug View Post
Hi Paula
Latest results as follows:-
All at 5v ampl/div

IC25 pins 6,11, I see a square wave, pins 2, 14 i see 12v on scope.

IC24 pins10,12 I see a square wave, pin 11 12v on scope, pin 13 is dead, nothing?

IC25 pin 5 pulsing seen

IC14 pin 7 pulsing seen

Found a dry joint on underside of board IC21 pin 15 but it is just an isolated pad so not sure it affect anything but will redo the joint.

Does the above mean IC24 needs replacing?

Regards

Mark
Is it exactly the same? If so we need to look for another reason pin 11 is stuck high. Can you put your scope on IC25 pins 6,11,14,2 just in case there is a break in the tracks to IC24.

Last edited by PJL; 17th Feb 2023 at 11:56 am.
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Old 17th Feb 2023, 6:33 pm   #107
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Default Re: Help needed with - Racal Dana 9081

Hello Mark,

As PJL has suggested above, you really need to repeat all the IC25 measurements with the replacement fitted. Pins 6,11,14 and 2 should all show a changing signal as there isn't anything to stop them counting in the absence of the PE pulse from TP16. If that pulse is actually present now it's possible that pins 14 and 2 won't count but they will be at 0V rather than 12V.

Paula
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Old 18th Feb 2023, 1:51 pm   #108
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Default Re: Help needed with - Racal Dana 9081

Hi all

The holes are PTH so have fitted an IC socket and put the other chip in i had, turned on and still exactly the same function wise. I will fire up the scope this evening with this IC in and repeat the measurements as recommended.
Thanks all
Mark
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Old 18th Feb 2023, 5:11 pm   #109
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Default Re: Help needed with - Racal Dana 9081

Hi all
Results of retest as follows:-
IC25 Pins 6,11,14 & 2 waveform
IC24 Pins 9,10,11,12 waveform seen
Pulse seen at pin 5 of IC25
Pulse seen at Pin 7 of IC14
Are there any other retests i should perform, i have a CF4029B on order and now i have the ic socket it will be easy to try or is IC25 working now?
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Old 18th Feb 2023, 7:14 pm   #110
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Default Re: Help needed with - Racal Dana 9081

Hello Mark

That's good to hear. The old IC25 was faulty, so check for the following.

There should be a 12V positive going pulse at TP16, about 500ns wide repeating every 400us, although that will depend on the exact setting of other controls. There should be a waveform of the opposite state at TP9 too, that is negative going 500ns pulses with +12V the rest of the time. If these pulses are present the divider circuitry is working properly. You then need to confirm that TP19 has a broad 12V with a 0.5ms 0V every 3ms. The timings again may vary with the step settings etc. If that pulse is present, the divide by 160/161 circuit will be have a chance of working too. With all this correct, the problem lies in the phase detector.


It's quite possible that the pulse at TP16 is still missing. If that's the case, check for pulses at TP15. If they are missing, replace IC24.

If they are present, check pin 11 of IC6 for pulses. If they are missing, check for pulses on IC6 pin 12 and 0V on IC6 pin 13. If both are correct but there are no pulses at pin 11, replace IC6.

If you do have pulses from IC6 pin 12, check that they are still present at IC 8 pin 12. If they are, check for pulses at TP8. Those will be 10us wide positive going pulses every 300us.

If there are no pulses at TP8, check IC8 pin 13. If nothing there, check IC8 pins 9, 10, 11 and 12 again. They should all have pulses. If they do, and there are none at pin 13, replace IC8.

With pulses at TP8. check that they are still present at pin 10 of IC10. If they are, check pins 15 and 14 of IC10. Both should be at opposite states, that is, pin 15 should be 0V with brief 12V pulses, and pin 14 should be at 12V with brief 0V pulses. If you're not seeing that, either IC10 or Q8 are faulty. You can check Q8 with the diode test method. If it measures good, change IC10. If bad, change Q8 and check for pulses on pins 14/15 again. If they are still missing, change IC10.

The key measurements are the pulses at TP16 and TP9. If they are both correct, the divider chains are working properly.

Report back your findings and we can move on from there.
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Old 18th Feb 2023, 8:14 pm   #111
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Default Re: Help needed with - Racal Dana 9081

Hi Paula
Results as follows:-

Mine is the other way round i.e
No 12v pulse at TP16 its at 0v
12v pulse at TP9

TP19 +12v on scope

TP16 still missing anything
TP15 missing anything

So i will change IC24 as the above two are missing as suggested.
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Old 18th Feb 2023, 8:15 pm   #112
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Default Re: Help needed with - Racal Dana 9081

I stopped at this point as the IC needed replacing.
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Old 18th Feb 2023, 10:10 pm   #113
frsimen
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Default Re: Help needed with - Racal Dana 9081

Hello Mark,

Before changing IC24, just check that there are pulses on all four input pins (9, 10, 11 and 12) just in case the main counter has stopped. If they are all present and there is no pulse on the output, IC24 has failed.

Paula
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Old 19th Feb 2023, 12:06 am   #114
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Default Re: Help needed with - Racal Dana 9081

If TP9 has a pulse but TP16 does not, there is something else wrong.
Does 'missing anything' mean it is 0V?
Can TP9 have a pulse if TP15 does not have one?
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Old 19th Feb 2023, 8:45 am   #115
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Default Re: Help needed with - Racal Dana 9081

Hi Paula, Peter

I have run the tests requested but this time taken a pic of the trace on the screen so you can see what I am seeing so there is no confusion, results as follows:-

IC24
Pins 9,10,11,12 - square waves observed as attached, pin 13 which i believe to tbe the output the trace line remains on the crosshair as set and doesn';t move at all when connected to Pin 13 of IC24.

Also noted that IC24 is a "CD4002AE" IC not a "CD4029AE" as we have been delaing with up to now, so looked up datasheet as was unsure which was output pin, please confirm pin 13 was correct to select for the output measurement?

I will show the test point measurements on the screen in next uploaed following this as can only attach 5 pics.
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Old 19th Feb 2023, 8:50 am   #116
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Default Re: Help needed with - Racal Dana 9081

Heres the test point measurements:-

TP9 - shows the trace jump to 12V

TP16 - nothing trace remains on the crosshairs exactly as it is before anythig connected by probe, so when i have said missing or showing nothing it means the trace doesn't move or show anything at all, as in the trace shown for TP16.

CD4002 - Thought i'd post pic showing the 4002 IC, so you have the same visibility of part code as me.

Please confirm if i need to change this or not based on above? if so I will need to order a 4002 as don't have one, only a spare 4029.

Thanks again

Mark
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Old 19th Feb 2023, 9:52 am   #117
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Default Re: Help needed with - Racal Dana 9081

Hello Mark,

The waveforms on the outputs of IC25 look good, so IC24 is giving every indication of being faulty. Have a quick look at the soldering under IC6 in case there is a short between pins 12 and 13 on that IC, as that could cause the same lack of output.

If there is no short, IC24 will need replacing. It is worth considering spares for IC6, IC15, IC22, IC8, IC10 and IC3 when you are placing your order. If there are other faults, you'll have the part and you will save a lot on carriage over buying one at a time. None of the ICs are very expensive from reputable suppliers.

Paula
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Old 19th Feb 2023, 10:31 am   #118
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Default Re: Help needed with - Racal Dana 9081

Hi Paula
Will check the pins of IC6 and if no short order a replacement IC24 and look at the others part numbers as suggested.
Thanks again and pleased with progress as would never have found this.
Regards
Mark
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Old 19th Feb 2023, 10:45 am   #119
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Default Re: Help needed with - Racal Dana 9081

Mark, before ordering any ic, give me a list and I will check my stock today and see what I have here. Just for cost of postage. Bearing in mind it is over 25 years since I did repairs on the sig gens.

Rob
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Old 19th Feb 2023, 6:11 pm   #120
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Default Re: Help needed with - Racal Dana 9081

I am following this thread with a combination of interest and amazement. I am NOT a "digital man".
However, for Mark, could I suggest you move your scope horizontal shift to always show the start of the trace. You will get a better idea of how each sweep is triggered, often very important, though maybe not here.
If the centre line of your vertical trace was at 0v (input switch set to ground position whilst adjusting trace, when you return it to DC coupled), you know that centre line is at 0v, so you can safely say 0v, not "nothing".
Of course for some good reason, you may sometimes set your centre line with (say) +12v, in which now "nothing" should be +12v.
I throw these comments in as you are admittedly not a fully paid up "scope man" and they may be helpful.
Cheers, Les.

Last edited by MotorBikeLes; 19th Feb 2023 at 6:12 pm. Reason: added "vertical".
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