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Old 8th Feb 2023, 8:47 pm   #61
3pinplug
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Default Re: Help needed with - Racal Dana 9081

Hi Paula, Peter
I fitted a new C11 (tant)that i put in recently the wrong way round and the voltage on Pin 1 of IC4 now spikes to 12v then drops back to zero. I conducted the other tests you mentioned and obtained the following results:-
Pin 7 IC4 - pulses seen
Pin 7 IC7 - pulses seen
Pin 7 IC20 -NO pulses seen
Pin 7 IC13 - NO pulses seen
All above when spinning spin wheel.

The pins you mentioned at end of last post, what IC number were those for?

Hopefully missing pulses will point us in the right direction!

Mark
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Old 8th Feb 2023, 10:26 pm   #62
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Default Re: Help needed with - Racal Dana 9081

Hello Mark,

One problem fixed, still a few more to find, I think.

IC20 should be dividing by 16, so you will need 16 pulses on the output of IC7 to see one pulse on the output of IC20, IC13 will need 8 pulses, I think, to get an output on pin 7, so will take a lot more spins of the wheel to see anything.

The ICs I was referring to are the same ones still. IC4, 7, 20, 13 and 23. You should see pin 6 change for every pulse going in on pin 5 for all of them except IC4, which is arranged slightly differently. For IC4, you should see the change for every clock pulse on pin 15. It's worth checking that all four pins (6, 11, 14, 2) on each IC change state just to confirm that all is well. Pin 11 will change at half the rate of pin 6. Pin 14 at half the rate of pin 11 and pin 2 at half the rate of pin14. The exact number of pulses needed to complete a count will depend on the initialisation values.

You may have found a fault, or you may just need to spin the wheel for a bit longer!

As a bit of a diversion, one further test which will identify if the VCO is actually locking is to switch the Fine Tune switch to INT. If the VCO is locked, the frequency on the display will change as the fine tune control is adjusted. If it doesn't change, or doesn't seem to change in step with the control, the VCO isn't locked. Go back to the OFF position at the end of the test.

Paula
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Old 8th Feb 2023, 10:38 pm   #63
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Default Re: Help needed with - Racal Dana 9081

Hi Paula
I will get spinning a lot more and check for the pulses as mentioned, thanks again. Regards
Mark
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Old 9th Feb 2023, 8:51 am   #64
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Default Re: Help needed with - Racal Dana 9081

Hi Paula
I did some tests but i think i am gping to repeat them as bit confused after doing them!
Could see pulses on Pin 7 on IC 4 & 7 - pin20 i get after spinning for a while. Not seeing much on IC13 but some on IC20.
Then measured pins 2,6,11,14 on each IC, pin 2 appears to have 12v on each Pin2 on each IC apart from on IC13 where i have 0.00v. Even after spinning the wheel no change.
Heres tge results of pin checks on IC13
Pin 2 no pulses or voltage.
Pin 6 voltage and pulsing
Pin11 voltage and pulsing
Pin 14 odd random pulse

Interesting this is In the area where i have that rogue tant soldered to the top side of the board that when i turned the unit on a while back it started smoking. Its between IC20 & 23.
I will repeat the above tonight as a double check.
Regards
Mark

Last edited by 3pinplug; 9th Feb 2023 at 8:52 am. Reason: Typo
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Old 9th Feb 2023, 6:29 pm   #65
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Default Re: Help needed with - Racal Dana 9081

The levels that you measure on the output pins, 2,6,11 and 14 will depend on the exact count that has been reached when you make the measurement. The values I gave earlier will only be seen when switched on and before the spin wheel/up/down buttons are touched.

If you get a chance to do the fine tune test I suggested as well, that may give another clue as to what is going on.

Paula
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Old 9th Feb 2023, 6:48 pm   #66
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Default Re: Help needed with - Racal Dana 9081

Something that will save your fingers when you are tuning can be found in the service manual on page 4-5. Table 2 gives a list of the number of pulses generated per step of the spinwheel or press of the up /down buttons. For the IC4 end of the counter, 1 pulse per step is ideal. At the other end, for IC23 64 pulsed per step would be preferable. You can select what suits you best for the other ICs.

For example, for 1 pulse per step, select the range 5 (256-512MHz) with 5kHz spacing. For 32 pulses per step, select range 2 (32 to 64MHz) with 25kHz spacing.

Paula
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Old 9th Feb 2023, 7:56 pm   #67
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Default Re: Help needed with - Racal Dana 9081

Hi Paula.

Did the fine tune test and neither of the controls altered the frequency when int is selected, the LED does light to show it is selected. So VCO could be unlocked as you suspected.

I will rerun the other checks I did in the morning. Whereabouts is the VCO located?

Regards, Mark.
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Old 9th Feb 2023, 8:25 pm   #68
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Default Re: Help needed with - Racal Dana 9081

Hello Mark,

The VCO is on the other side of the chassis, below the phase detector. The VCO is running just fine, the problem is more likely to be on the phase detector board than the VCO from what you've reported so far.

Now that you have shown that the circuit doesn't seem to be locking properly, have a look at what is present on TP9 and TP10. If you can measure the frequency that you find there, so much the better. Try these measurements for 25kHz spacing on each band other than 5-32MHz.

Sorry to ask for so many checks to be made but it's the only way that a picture can be built up of what is going on.

Paula
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Old 9th Feb 2023, 8:33 pm   #69
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Default Re: Help needed with - Racal Dana 9081

Hi Paula
Happy to conduct all these tests, you and Peter have been so helpful taking time to help me out, it is really appreciated.
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Old 9th Feb 2023, 9:23 pm   #70
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Default Re: Help needed with - Racal Dana 9081

Hi Paula
Performed the measurements on TP9 and 10 with 25khz spacing:-
TP9
32-64mhz = 2.29mhz and frequency slowly rising , not a steady reading
64 - 128mhz = 2.38mhz and as above slowly rising.
128-256mhz = 2.53 rising s above slowly rising
256-520mhz = 2.46mhz and rising slowly.

TP10
32-64mhz = 0.41mhz fluctuating and slowly rising
64-128mhz = 0.42mhz fluct and slowly rising
128-256mhz = 0.42 mhz as above
256-520mhz = 0.16-0.17mhz fluctuating
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Old 9th Feb 2023, 9:52 pm   #71
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Default Re: Help needed with - Racal Dana 9081

Hi, Back again, been working away for most of the week.

Just catching up.

First, those tests you made on the Logic board proove that it is working perfectly, so as you have done move onto the next stage.

I wont interfere at moment, as two diagnostic routes can be very confusing....

Just quick question. What is displayed on the led displays? (when pin 15 and 17 of logic board are connected)?

Reason I ask is the display is a true frequency counter, reading the output frequency. This can so a lot about where the fault isn't

Did you resolve the issue with 37.5kHz only reading 30kHz?

To test the VCO you can disconnect wire from pin 1 on divider/counter board, and connect an isolated output variable PSU to the wire. You can then steer the VCO using the PSU. Just watch the voltage doesn't get too high....start at 0V and increase voltage very slowly...The display should show actual frequency.

Doing this you can test the function of the Phase detector by measuring TP9 and TP10, TP1 and TP2, and finaly TP4 and TP5.
As the frequency on TP9 and TP10 match, the output TP1 and TP2 should swap state, and pin 1 should change between low and high voltage.
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Old 10th Feb 2023, 7:50 am   #72
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Default Re: Help needed with - Racal Dana 9081

Hi Paula, Peter
Some more rsults form testing and observationbs:-

1. Peter - yes did resolve the 30khz issue, switch was wrong as suggested, reads spot on - see pic.

2. Pauls - Revisited the IC pins test, confirms results:-

All conducted on pins 2 & 6 of the IC's
IC23 - No pulses either pin
IC4 Pulse on both pins
IC7 - Pulses on both pins
IC13 no pulses on either pin

So IC13 & IC23 not receiving the pulses they are supposed too?


3. I also attach a pic of the board and two IC's that caught my eye as they look to have either had the solder joints touched up (can see in pic) or been replaced. These are IC21 & IC14 in the pic of the board, are they the correct type?

4. From memory When 15 & 17 were disconnected I lost any frequency display it just showed 0.000v i seem to remember as was worried i had lost display. But back now all wires connected but still getting incorrect reading as reported.

Regards

Mark
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Old 10th Feb 2023, 1:57 pm   #73
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Default Re: Help needed with - Racal Dana 9081

Hello Mark/Peter,

Peter

Feel free to jump in if you think I'm missing something obvious.

Mark

Your measurements at TP9 and TP10 are well off what I was expecting. Some are also beyond the frequency that 4000 series CMOS will work reliably at, so something is definitely wrong. Check with your oscilloscope to see what is going on.

IC13 and IC23 should receive pulses on their clock in pins, although they will be a lot further apart than on the earlier ICs. Look for a pulse on the output of IC20 (pin 7) and check that it reaches IC13 pin 5. You will need to turn the spin wheel a good few times to get a pulse at pin 13. Do check that the UP/DOWN line (pin 16 on the edge of the board) is at 12V to make sure that the counters are going up, rather than down. If it is at 0V, you will need to turn the spin wheel in the other direction! Once you are seeing pulses on the input to IC13, check that pin 6 changes state. If it does, look for a pulse on the output (pin 7). You will need to spin the wheel for a good while to see the change. Once you do, check pin 6 of IC23 to see if it changes state.

It's possible that all 5 ICs are working, just that you haven't seen the change of state so far. If there never is a change of state, despite much spinning of the wheel, IC20 could be faulty.

The new ICs in the are 4029Bs. The originals were 4029As. Functionally they are the same, but there are a few subtle differences. The B versions don't work well with slowly changing waveform edges, which can cause them to oscillate. The noise immunity of the B version is somewhat better than the A. I don't think either difference will cause a problem here. The maximum operating frequencies of both types seem identical from the data sheets.

Just one other point, do you still have the wires from the step up and step down outputs to the Logic board disconnected? They should still be disconnected, otherwise they are going to be fighting with your fault finding efforts, in particular it will force the UP/DOWN line to DOWN.

Paula
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Old 10th Feb 2023, 7:16 pm   #74
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Default Re: Help needed with - Racal Dana 9081

Hi Paula
Sorry - No unfortunately i have all the wires connected at present, which numbers dhall i disconnect and what tests will need doing again due to that. I will recheck the ic pins etc as suggested.
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Old 10th Feb 2023, 8:26 pm   #75
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Default Re: Help needed with - Racal Dana 9081

Hello Mark,

Before doing anything else, just check if you are still getting pulses on terminal 15 of the phase detector board, without touching the up/down or spin wheel. Also check on pin 7 of IC4. If there are no pulses being generated, that's good and the wiring can be left alone. Report back if there are no pulses as that indicates that an earlier problem has been resolved.

If you are still getting pulses, disconnect the wires to terminals 15 and 17 on the logic board. There is no need to repeat all the tests. Start at the output (pin 7) of IC20 then move on to ICs 13 and 23, as described in post #73 above.

Don't forget to have a look at TP9 and TP10 with your oscilloscope. You should be seeing a signal of a few kHz, rather than MHz. I would expect the frequency of the pulses on TP9 to be rather higher in frequency than those on TP10.

Paula
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Old 10th Feb 2023, 10:15 pm   #76
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Default Re: Help needed with - Racal Dana 9081

Hi Paula
Already conducted some of the measurements, results as follows:-
Pin15 (wire connected) no pulses, pin 7 IC4 no pulses

32-64 range TP9= 1705khz. TP10= 5.045khz
64-128 range TP9=1703khz. TP10= 5.043khz
128-256 range TP9 = 1700khz TP10= 5.044khz
256-520 range TP9 = 1699khz TP10= 5.045khz

Both the valves for TP9 and TP10 last digit fluctuating and sometimes changing 2nd to last digit.
Perform rest in morning👍
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Old 11th Feb 2023, 12:37 am   #77
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Default Re: Help needed with - Racal Dana 9081

Hello Mark,

There has been some progress in that the out of band detector circuit now doesn't think the N counter is generating an out of band count. C11 could well have been the cause of that.

The frequency at TP10 is about right, so the reference frequency now is correct. What you are seeing at TP9 isn't right. Could you check the actual waveform there with your oscilloscope, paying particular attention to the amplitude. I wonder if there is only a very low level of noise present on TP9, rather than a proper divided down signal.

The signal applied to the phase detector board is 128-256MHz when working properly. 1.703MHz is quite close to the 270MHz or so that you saw on range 4, divided by 160, which is carried out in the ECL part of the circuit on the left hand side.

I think you can leave the circuit around ICs 4, 7, 20, 13 and 23 as it seems to be working well enough.

There are plenty of test points in the top part of the circuit. A quick look at each one for a good (10V+) switching waveform should show any problems. Start at TP17 and 18. If they look good, move to the right and check the test points over towards TP10. If TP17 or 18 look bad, move to the left and check the test points TP20 and TP26. The voltages there will be lower, but you should still see a distinct pulse and that will be at around 1.7MHz.

Paula
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Old 11th Feb 2023, 12:17 pm   #78
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Default Re: Help needed with - Racal Dana 9081

Hi Paula
Results of measurements as follows and took pics of the waveforms in case that helps as well.The voltage measurements were taken with DVM on the test point.

TP17 - No visible waveform and reading 0.00V
TP18 - Waveform observed, reading 6.98v
TP9 - No waveform, reads 12.31v
TP10 - Waveform observed, reads 12.31v
TP20 - Waveform observed, reads 4.18V
TP21 - Waveform observed, reads -1.19v

Do i need to repeat the above with my frequency counter oin the pins or is the fact that TP17 & TP9 not having a waveform highlighting a problem?

Regards

Mark
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Old 11th Feb 2023, 12:18 pm   #79
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And the last two pics of testpoint waveformshot, photos filename is the name of the test point
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Old 11th Feb 2023, 2:05 pm   #80
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Default Re: Help needed with - Racal Dana 9081

Hello Mark,

There's quite a lot that isn't right from your photos. I have measured the results from my 9082, which is very similar the 9081, so the results should be valid. The generator was switched to the 64-128MHz range and tuned to the highest frequency, 134.9MHz, tuning set to fast and 6.25kHz steps.

Starting at TP17. There is a 10V peak to peak near square wave of period 600ns.

TP18, I couldn't identify positively, but what I think is TP18 has a similar waveform to TP17.

TP19 has a waveform that is 12V for 2.5ms and 0V for 0.5ms, repeated.

TP20 has a square wave with some ringing. The base line is about -1V and it rises to +10V. Period 600ns.

TP15 has a 3ms period near square wave, 12V peak to peak.

TP14 has a tricky to trigger on waveform. The base line is at +12V, with 0V pulses of 600ns width every 200 microseconds.

TP7 has 12V pulses that alternate between a single pulse and a double pulse. All pulses are 10 microseconds long, and the double pulses are separated by about 10 microseconds. Between the start of the double and the single pulse is 175 microseconds, from the start of the single pulse to the start of the double is 150 microseconds.

TP8 had 12V 600ns pulses, every 330 microseconds.

TP9 and 10 both have a very short 0V pulse on a +12V baseline when locked. The pulse is too short to measure accurately with my 'scope.

From the above, your problem seems to be early on in the divider chain. Check TP19, I expect that won't be right either. The counters won't do much counting unless the clock is present and that is missing at TP17, before it reaches the counters.

It would be worth checking that Q6 and Q7 are in good health, although if the voltage at TP19 is permanently high that will be enough to stop things working all on its own. To confirm that the clock is missing, check pin 15 of IC5, where you should see a waveform that matches what I had at TP17.

Paula
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