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Old 1st Feb 2023, 3:07 pm   #41
Cruisin Marine
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Default Re: Help needed with - Racal Dana 9081

Quote:
Originally Posted by 3pinplug View Post
Here's what the display is showing:-
5-32MHz - displays 0.000
32-64Mhz - displays 67.688
64-128Mhz - displays 135.376
128-256MHz displays 270.754
256-520Mhz - displays 541.358
I don't know these that well, not even seen a block diagram, but suspect a mixer is not functioning.
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Old 1st Feb 2023, 6:43 pm   #42
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Default Re: Help needed with - Racal Dana 9081

The main VCO is being driven to its highest frequency from what you have observed. That could have many different causes, so the problem will take some tracking down.

For the time being, don't worry about the lack of response from the spin wheel and up/down buttons. The 9081 should start up on roughly 384/192/96/48MHz, the exact frequency depending on the channel spacing selected. The lack of output on the lowest frequency range could indicate a fault in the 120MHz loop, but that is at least partially working otherwise the counter wouldn't work.

I suggest you turn your attention to the phase detector board initially. Check that there are no shorts on any of the supply rails, leaving open circuit resistors or chokes on the board. There may still be a faulty tantalum capacitor lurking somewhere. If all the supplies are present, have a look at the various test points on that board for signs of pulse activity.

The output vernier control does seem to get very difficult to turn on these. A small drop of lubricating oil on the metal shaft made a big improvement to mine.

Paula
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Old 1st Feb 2023, 7:28 pm   #43
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Default Re: Help needed with - Racal Dana 9081

Hi Cruisin marine snd frsimen,
Thank you for the info, just had a look at the divider and phase detector and theres certainly a lot voltages to check on there, may take a couple of days.
Regards
Mark
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Old 2nd Feb 2023, 10:25 pm   #44
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Default Re: Help needed with - Racal Dana 9081

Hi all
Using the circuit: divider and phase detector assembly 19-0846 schematic and component layout: Divider and phase detector assembly 19-0846 drawings I embarked with my dvm to check all the points showing +12v, +24v and -5.2v etc.

Here's a summary of the findings:-
Tp1 and pin 2 of IC29 only read - 1.2v not -5.2v as indicated on schematic. Could Q1or Q2 be the cause of thoes low voltage?

R41 and R42 both had 12.31v on one side, R42 other side showed 11.21v whereas R41 read 0.00v on the other side. Could R41 be faulty?

There is a weird shaped piece of solder underneath C11 so need to investigate this further. Attach pic of this!


All other voltages shown read fine. Any advice on above results?
Many thanks
Mark
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Old 3rd Feb 2023, 12:45 am   #45
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Default Re: Help needed with - Racal Dana 9081

Hello Mark,

The 5.2V marked by TP21 is referring to the voltage applied to R2 and R3. There will be some sort of pulse waveform on TP21, not a steady voltage.

The voltage you read on R41 will depend on the setting of the channel spacing switch. Try the switch in different positions and the voltage will jump back up in some positions. I doubt that there is anything wrong with R41.

Your next move should be to measure the voltage across the various tantalum capacitors, eg. C4(should be close to 12V), C22 (should be close to -6V) C16 (could be over 20V) etc. Check also the voltage at the junction of C11 and R33, which is used to reset the divide by N counter. You may see a blip when power is applied but it should drop shortly afterwards. If any of the voltages measure much lower than expected, the associated tantalum capacitor is suspect and may have damaged the feed resistor.

If all the voltages are fine, how you move on will rather depend on what test gear you have. An oscilloscope would be ideal, a logic probe would be better than nothing, although it may not work in the ECL part of the circuit.

Paula
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Old 3rd Feb 2023, 1:09 am   #46
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Default Re: Help needed with - Racal Dana 9081

Quote:
Originally Posted by 3pinplug View Post

Here's what the display is showing:-
5-32MHz - displays 0.000
32-64Mhz - displays 67.688
64-128Mhz - displays 135.376
128-256MHz displays 270.754
256-520Mhz - displays 541.358
If the output is pegging over to maximum, one possible cause is the logic board . This would also likely explain lack of Spinwheel and switch function.

Band edges are detected by the PROM, and send out a signal, that is converted into pulses either step up or step down if the band edge has been crossed, steering it back into the band. If this is the case, then the signal generator is basically working, but the UP/Down detection is not working, so always running in the wrong direction, to the band edge!.

Check to see if you have any pulses on the pins 15 and 17 on logic board. If you do, see if they are up or down pulses. Check the UP/Down output corresponds with the directions on pin 13. Temporary reverse the wires to these pins to test the up/down output switches correctly.

Also check for pulses on pin 18 of logic board to see if the pulse generator is driving the counters/dividers when it should not.
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Old 3rd Feb 2023, 10:12 am   #47
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Default Re: Help needed with - Racal Dana 9081

The capacitor C11 picture looks like some I have seen in the past where they have "blown". Instead of the usual charred remains, a small hole appears and silvery "stuff" is deposited close by.
Worth replacing it I think.
Rob
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Old 4th Feb 2023, 9:03 am   #48
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Default Re: Help needed with - Racal Dana 9081

Hi all.

Firstly thank you for all the help / pointers really good of you all it's very much appreciated.

Paula - I will check the tants suggested and see what I find, also I do have a 50MHz dual trace oscilloscope. Sounds like it may be useful to have this moving forward.

Peterg0rsq - will conduct the exercise on pins 15,17, 13 & 18.

Robinshack - will change C11 as suggested, test it and post a pic of the underside showing in more detail what that bit is / has originated from.

Will report back with the results to all of the above.

Thanks again

Mark
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Old 4th Feb 2023, 6:45 pm   #49
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Default Re: Help needed with - Racal Dana 9081

Hi all
Right heres the readings / findings, hopefully I have done these correctly.

C11 - desoldered it and found it was just a lump of solder on the leg - see attached pic. There was only 6 tants on the divider & phase detector board so took the opportunity to replace them all!. All were pretty much to spec apart from"C1" which read as a resistor so was not working, so glad i did this afterall. Checked the resistor associated with C1 and it was ok.

Checked Pins 15, 17, 13 and 18 on the Logic board on my oscilloscope looking for pulses, assuming thats the correct way to do it?
Results were
Pin 15 - Pulse (waveform?)- pic attached
Pin 17 - nothing
Pin 13 - Nothing
Pin 18 - Brighter pulse (waveform?) than Pin 15 but looked the same waveform.pic attached.

Didn't change the pins round as 2 had nothing and one (Pin 18) was working as it should.

Tantalum Voltage on + leg of Tants on Divider and phase detector board after replacement:-
C6 = -5.07v
C22 = -5.51v
C1 = +12.32v
C4 = +12.29v
C13 = +7.36v
C11 = +12.30v (tant that was found to be dead)

I have tried the unit since replacing all the tants and still in exactly the same condition, hopefully the above gives the next pointers to look at?

Thanks again all

Mark
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Old 4th Feb 2023, 10:28 pm   #50
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Default Re: Help needed with - Racal Dana 9081

Quote:
Originally Posted by 3pinplug View Post

Checked Pins 15, 17, 13 and 18 on the Logic board on my oscilloscope looking for pulses, assuming thats the correct way to do it?
Results were
Pin 15 - Pulse (waveform?)- pic attached
Pin 17 - nothing
Pin 13 - Nothing
Pin 18 - Brighter pulse (waveform?) than Pin 15 but looked the same waveform.pic attached.

Didn't change the pins round as 2 had nothing and one (Pin 18) was working as it should.



Mark
Mark

As I suggested the signal generator is essentially working, but the band edge steering is driving the signal generator to the maximum edges.

On the logic board disconnect wire on pin 15. This should also stop the pulses on pin 18. If not there is a fault on the logic board, which is oscilating.

Now turn spinwheel one direction, then the other. You should see the logic at pin 13 change state depending on the direction of rotation.

If you do not see it change state, then you have a fault with UP/Down detection on the logic board.

What I suspect is happening is the band edge detector circuit (Around the PROM) has detected the frequency is out of band, and firing pulses to lower the frequency. It appears to be doing this (as the frequency is not going any higher, (it will eventually try to go so high that it stops the main oscilator and out put drops to zero) but as soon as the frequency comes back into range (by a few Hz) the Band edge detector turns off its control, but the output of the generator continues to go up, triggering the band edge detector again

Its a little complicated to describe as it is a closed loop system controlling the band edges.

Frequency goes 1 Hz over band edge, then control logic sends down pulses to pin 15 which lowers the output frequency by a few Hz
As soon as output goes 1Hz below band edge (due to down pulses) the band edge control stops, but something is then driving the output frequency up again, so the band edge control kicks in.

I suspect everything is working well (Counters, dividers, phase comparitor and reference oscilators, but the issue looks like it an oscilation on the logic board, but do the checks described to confirm it.
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Old 4th Feb 2023, 10:36 pm   #51
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Default Re: Help needed with - Racal Dana 9081

Your measured voltages on the phase detector board all seem to be reasonable now.

The measurements on the logic board are encouraging. Pin 17 will only have a very brief spike when you operate the switch, so I wouldn't be too worried about that for now. Pin 13 should change from high to low or low to high as the direction of the spin wheel is changed. If you only turned the spin wheel one way, or only pressed the up or down button, the voltage at pin 13 wouldn't change.

I would go back to the phase detector board and check for waveforms at the various test points on that. For clarity, you will need to be careful to say TP for a test point or a plain number for one of the termination points, otherwise things will get very confusing. A rough measurement of the frequency (or period) of any pulses would be helpful too.

If you can use the following settings it will make it easier for your results to be checked against a working unit:

Tuning speed: Fast
Range: 128-256MHz
Steps: 25kHz

Your 50MHz oscilloscope won't be able to display anything useful from the input to the dividers, as the 128MHz to 256MHz is well outside its bandwidth. Further down the chain you should see trains of pulses.

There is also a useful looking 37.5kHz reference signal on pin 18 that should be checked.

These checks should help to identify if the signal from the VCO is being divided down and fed to the phase detector.

I wrote the above before seeing Peter's reply. Do his checks first, they are likely to get you to a successful outcome quicker than my method!

Paula
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Old 5th Feb 2023, 11:15 am   #52
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Default Re: Help needed with - Racal Dana 9081

Hi Peter , Paula

Here are the results of the tests, I was keen to see what they showed:-

Disconnecting pin 15 removed pulses from pin 18.

At rest ie not moving spinwheel I positioned trace in centre of screen on oscilloscope, moving spinwheel anticlockwise - no movement! trace stayed in same position as at rest.

Turning spinwheel clockwise trace jumps upwards on screen.

I attach two pics - one at rest / moving spin wheel anticlockwise.
One showing movement of trace upwards when rotating spinwheel clockwise.

From your instructions, does this now indicate I have a fault with the up / down section on the logic board?

I tested the spin wheel with Pin 15 still disconnected as you didn't say to reconnect it for the second test, hope that was correct?

Regards

Mark
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Old 5th Feb 2023, 10:39 pm   #53
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Default Re: Help needed with - Racal Dana 9081

Quote:
Originally Posted by 3pinplug View Post

Disconnecting pin 15 removed pulses from pin 18.
Good, as expected.

Quote:

At rest ie not moving spinwheel I positioned trace in centre of screen on oscilloscope, moving spinwheel anticlockwise - no movement! trace stayed in same position as at rest.

Turning spinwheel clockwise trace jumps upwards on screen.
What pin/testpoint? Pin 18 or pin 13? Volts/div?

Quote:

I tested the spin wheel with Pin 15 still disconnected as you didn't say to reconnect it for the second test, hope that was correct?
Correct

For all future tests disconnect pins 15, 17, 13, and pin 18.

Measure pin 13. Does state change between 0V and 12V when you flick "UP/DOWN" switch one way, then the other?

Same for clockwise, and anti-clockwise rotation of spin wheel?

Now measure pin 18. Are there any pulses showing when not operating controls? Should be non.
You should see pulses when operating spin wheel and up/Down switch.

In my manual there is table 2 in section 4.37. set the channel size to 5kHz and band to highest frequency band (band 5). Flick the up/down switch. Do you see a single pulse (pin 18)? It will be narrow, at about 1.6uS wide. Try the other settings in the table, but i is not important at the moment. Without a storage scope it is difficult to count them! If you have an analogue scope trigger on them to see them.

While on the board check you have 37.5kHz on pin 10.

If it passes all these tests then the Logic board is working fine.
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Old 5th Feb 2023, 11:22 pm   #54
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Default Re: Help needed with - Racal Dana 9081

Hi Peter
The scope traces were taken with pin 15 disconnected and my scope probe on pin 13. The volts / div was set to 5v.

Ok i will disconnect the wires suggested snd do some further measurements. The manual i have has table 2 but on a different page, mine appears to be a combined 9081 & 9082 manual, do you have just the 9081 manual?
Regards
Mark
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Old 6th Feb 2023, 8:41 pm   #55
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Default Re: Help needed with - Racal Dana 9081

Results of tests requested;-

Pin 13 - state does change between 0-12v when I press the flick switch. Up /down. Up = 12v, down = 0v.

Same effect voltage wise for spin wheel, clockwise 12v, anticlockwise Ov.

No pulse seen at pin 18 when idle.

Pulses seen at Pin18 when I spin wheel in either direction and flick up / down switch either way. Interesting to observe all this!

Set channel to 5kHz and highest band -yes did see pulse on pin 18 when flicking up down switch.

Was there 37.5kHz on pin 10? I recorded 35 kHz on pin 10.

So does this confirm logic board OK? I have left the 4 pins disconnected in case next set of tests requires the same. Thanks again for helping with this Peter and Paula you certainly know your Racal Danas. 👍
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Old 6th Feb 2023, 10:47 pm   #56
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Default Re: Help needed with - Racal Dana 9081

35kHz might be correct if you have the fine tune control switched to INT. If you switch it to OFF you should be measuring 37.5kHz.

Certainly, there is nothing now on the logic board that can be causing the out of range signal to be generated.

From the block diagram, there are only four signals passing from the logic board to the divider /phase assembly:
Up/Down Pin 16
Pulse Pin 15
Special Channel Select Pin 4
37.5kHz pulse. Pin 18

Of the above, only the Up/Down and pulse feed into the N counter, formed from IC4, 7, 20, 13 and 23. These 5 ICs make an 18 bit counter.

The states of the 8 most significant outputs are used to address the ROM IC16, which provides the out of band control along with an additional feed from the bandswitch which indicates when the 5-32MHz band has been selected. The output of the ROM is fed via a multiplexer, IC11 before driving the step up/step down circuit. The multiplexer output will be enabled/disabled by a clock signal from IC19.

When first switched on, the counter should initialise to values which have been programmed in to each IC via their ABCD inputs (by connecting them to either 0V or 12V). This relies on a pulse, generated by C11/R33, being fed into pin 1 of all five ICs to allow them to set up properly.

If there are no pulses coming in on pin 15, the counter should stick to the pre-programmed values if it is working correctly. Those values are what makes a working generator start up somewhere near the mid frequency of the selected range. When pulses are received on pin 15, they will increment or decrement the output of the counter, depending on the state of the Up/Down control line.

The counter output is then used to program the divide by 160/161 and the divide by N counter at the top of the phase detector circuit, which divides the VCO frequency down to feed to the phase detector.

The out of range logic is operating, which suggests that the output of the N counter (IC4, 7 etc) is not in the range that it is expected. The frequency display confirms that the output frequency is being commanded higher than it should be. The out of range signal will appear to pulse on and off all the time the count is out of range due to the clock feed from IC19.

It would appear that there is a problem in the N counter circuit, so the following should be checked, with the input to pin 15 on the phase detector board connected. Leave the connection to pin 15 on the logic board disconnected to stop the constant stream of pulses from the out of range down pulse circuit.

Check that 12V is present on pin 16 of ICs 4, 7, 20, 13 and 23.

Switch off and check for continuity from the junction of C11 and R33 to pin 1 of ICs 4, 7, 20, 13 and 23.

Connect the oscilloscope probe to pin 1 of IC4. Switch the generator on and confirm that a short 12V pulse is seen. It should back drop to 0V.

Check that there is no sign of a pulse waveform on pin 7 of the IC 4,7 20,13 and 23.

Check the outputs which feed the address lines of the ROM, IC16 as follows:

IC23 check pin 6 - it should be at 12V, pin 11 should be at 0V.

IC13 Pin 6, 11 and 14 should be at 0V, pin 2 should be at 12V.

IC20 Pins 2 and 9 should be at 0V.

The other pins don't feed directly into the ROM circuit, so won't cause the out of range signal to be generated. Check the soldering of any ICs which don't have the correct output, particularly the A, B, C and D input pins.

Hopefully, one of the tests above should reveal the culprit.

Paula
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Old 7th Feb 2023, 8:42 pm   #57
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Default Re: Help needed with - Racal Dana 9081

Hi Paula,
Carried out all the tests and all performed as you specified apart from two!

Firstly, i do not have continuity from junction of C11 /R33 to Pin 1 of IC7 when the unit is off.

Secondly i connected oscilloscope to pin 1 of IC4 and switched on, it spikes to 12vas suggested but then settles at 10v, it does not return to zero unless I switch unit off.

Looks like we are homing in!

Regards

Mark

Last edited by 3pinplug; 7th Feb 2023 at 8:43 pm. Reason: Typo
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Old 7th Feb 2023, 9:37 pm   #58
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Default Re: Help needed with - Racal Dana 9081

Hello Mark,

I've checked the diagram again and I was wrong. Pin 1 of IC7 is not connected to the other pin 1s, so what you have measured is correct.

The pins I listed for IC20 are incorrect, I should have said to check on pins 14 and 2, both should be at 0V. I muddled up the pin numbers on the diagram.

The C11/R33 measurement is not correct, so that deserves more attention. Check that C11 is the correct way around firstly. I think you have fitted a new one already, so I hope that is a good component and not leaky. Also check that you measure 220k from the negative leg of C11 to chassis. A cracked track, bad joint or faulty R33 could all cause the problem here.

You could try turning the tuning spin wheel a few turns and look for pulses from pin 7 of IC4. You should see several pulses as it is turned. Move along to pin 7 of IC7 and look for pulses t should be 0V.there. They won't be as frequent as the ones from IC4. If you see that, move along to IC20 pin 7 then IC13 pin 7. The pulses will be further apart as you step along the IC chain. If nothing else, that should prove that the N counter is working. If you look at the output pins 2,6,11 and 14, you should see them changing state on the counter ICs as you tune.

I'm a bit puzzled though. If all the other measurements were as stated above, why is the frequency not settling in the mid range and why is the limits circuit complaining? I'm not sure the battle is over yet.

Paula
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Old 7th Feb 2023, 10:23 pm   #59
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Default Re: Help needed with - Racal Dana 9081

Hi Paula
Many thanks, yes i did fit a new c11 i will check this and the other items first thing in the morning. Really appreciate all the help with this, thanks again.
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Old 8th Feb 2023, 8:29 am   #60
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Default Re: Help needed with - Racal Dana 9081

Hi Paula
Yes you were spot on i had fitted C11 when i replaced it recently the wrong way round!!! I have fitted a new one ( correct orientation) and also checked the others i did on the board and they are all ok. Unfortunately run out of time as off to work now but will conduct the remainder of tests this evening. I also forgot to confirm for Peter i read 37.501khz when i rechecked, i had knocked one of the flick switches.
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