Help needed with - Racal Dana 9081

[frsimen]

Hello Mark,

This has moved into the making no sense at all territory, from what you are reporting.

Could you check the following:

IC23 pins 6 and 11. At switch on, they should both be at 0V, but I suspect that pin 11 will be found at 12V. If pin 11 is 12V, please check for a brief 12V pulse on IC 23 pin 1, which should drop to 0V. If you're not getting that, check around C11/R33 and for continuity from their junction to pin 1 on each of IC4, 7, 20, 13 and 23.

If the reset isn't happening properly, that could account for some of the strange things you are reporting.

If all seems well with the reset pulse at switch on arriving at all the pin 1s, but IC23 pin 11 is still 12V, change IC23.

Paula

[3pinplug]

Hi Paula
Error straight away, i get the following:-
Ic23 pin 6 is 12v
Ic23 pin 11 is 0v

As i have 0v at pin 11 should i do the rest of the tests to check the affect of pin 6 being incorrect?
Regards
Mark

[frsimen]

Hello Mark,

The pin 1 tests are important as they should force the count to a known value when power is applied. Both pin 6 and 11 should be 0 at start up, but may not be right if the reset pulse on pin 1 is missing.

Paula

[3pinplug]

Hi Paula
Checked continuity from c11/R33 to pin 1 of IC4,20,13,23 all was goid, no continuity so checked doagram and pin 1 not connected to rest of pin 1’s i beliveas no continuity from this pin 1 to c11/R33.
When switching on all 4 pin 1’s that had continuity (4,20,13,23) the trace jumped up screen (to approx 12v) then slowly settled back down to zero.
Still got +12v on pin 6, 0v on pin 11 of IC23 so will change this now.
Regards
Mark

[3pinplug]

It was IC 7 pin 1 that had no continuity, checked diagram and that does not appear to be connected to the other pin 1’s., so looks to be correct?
Changed IC23, the reset pulse on pin 1 of ic 23 is present. Still got +12v pin 6. and 0v on pin 11. Howver the start up frequency on all bands has changed to the following:-
0.00
49.475
99.950
197.935
394.900
Ican also scroll up and back with the wheel.

[frsimen]

Hello Mark,

That sounds more promising. The actual start up frequency changes quite a bit depending on the step size you have selected, but what you have doesn't seem unreasonable.

At this stage, try reconnecting the wires to terminals 12 and 13 to see if you still have tuning control and, hopefully, the lowest frequency range will start to work again.

Paula

[3pinplug]

Hi Paula
Thanks again for all your assistance to date, really appreciate the help.
Will reconnect the wires and check if band 1 returns.
Regards
Mark

[frsimen]

Hello Mark,

Before reconnecting the wires to terminals 12 and 13, just check that you can tune over the whole range of frequencies on each band. That is, on band 5 you can tune down to 256MHz and up to 520MHz, band 4 from 128MHz to 256MHz and so on. You should be able to tune beyond the limits as there is nothing to stop you going out of range.

On range 1 if you tune down from the start position, you should reach a point where the counter bursts into life and you should be able to tune down to 5MHz.

If all this works, reconnect the wires to terminals 12 and 13. There is a possibility that this will return you to only being able to tune down in frequency from the start point. If that happens, there is a fault in the end stop circuit.

Paula

[3pinplug]

Hi Paula
Had reconnected all the wires and only seen post above when reporting back, no problem going back in to disconnect them but after connecting wires 12 / 13 unit is now as follows:-
On low band i now have full spin wheel control (up or down) from 4.8mhz to 36.7mhz.
Next band same again from 31.2mhz to 39.1mhz
Next band same again from 62.4 - 78.3mhz
Next band same again from 129.8mhz - 156.7 mhz
Top band 249.6mhz to 313.5mhz
Channel spacing set at 10khz.
So although i seem to have wheel movement and frequency control i don’t seem to have the right bandwidth, would there be a setting on the unit itself I may have in the wrong position. However another step forward as the wheel is now working up and down in frequency. Do you want me to disconnect the wires and go back in?
Regards
Mark

[frsimen]

Hello Mark,

No, I don't think you need to remove the wires again as you have already seen the output frequency was going well above the current ranges.

The problem now is that the end stop circuit is stopping the tuning going to the correct upper limit, apart from range 1. This is an area of the circuit which will be more difficult to fault find in and the ROM complicates matters. I haven't looked too closely at how this is supposed to work, so I'll have to spend a little time to try to understand the circuit better.

It would be helpful if Peter has some suggestions, as he has worked in this area and will know a lot more about its operation than I do.

In the mean time, try some checks that the step sizes displayed for each of the positions of the switch are correct and to find out if some step sizes give a wider frequency coverage than others.

Paula

Paula

[Chris55000]

Afternoon Mark!

Yes I would change IC23!

My offer of a replacement panel is still open if you desire it!

Chris Williams

[3pinplug]

Hi Paula
I still have the unit set up at present so will run the step size checks as suggested.
Regards
Mark

[3pinplug]

Hi Chris
I do not know if the change of board would resolve the issue to be honest, is it definitely known good board? that side of things is beyond me as taking the lead from you guys on here - what do you all think?

IC23 has just been changed which brought the improvement regarding the use of the spinning wheel on the frequencies i have in both the up and down direction.

Regards

Mark

[PETERg0rsq]

As already said disconnecting pins 12 and 13 to remove the band edge circuit from the equation.

With these pins disconnected do you still get limited tuning range? If yes then Band edge detection is NOT the issue (but 1/2 octave detection might be an issue)

If you still have a problem with 12 and 13 disconnected have you checked the IC's 4, 7, 20, 13 and 23 operate correctly as per the description in the manual. They are not all divide by 10's.

They should divide the pulses coming in, and send a carry out bit to the next chip.

Check this by monitoring the lines to the prom (A1 to A8), and check for correct binary counting on them. The most significant bit (A8) might only change state once in the full range of tuning (Keep wires 12 and 13 disconnected while testing).

A logic analyser is the perfect tool for this, even a very basic one. If you dont have one make one from 8 LED's and resistors to indicate the logic lines. Picture shows a basic logic analyser monitoring the pins as spin wheel is rotated, to see binary counting works.

If these are good then check the 1/2 octave bit is switching at the center frequency of the band. If it isn't then you will need to investigate the PROM circuit.

Band edge control and 1/2 octave switching works by looking at the output from the N-Counter and comparing it with a pattern stored in the PROM.

NOTE The stored pattern is different for the lowest band

So input to PROM is the most significant digits of N-Counter (A1 to A8), and one bit (A0) = 0 for range 1.

It uses a lookup table in the PROM, and outputs Six bits, in three sets of two (upper and lower band edge detected on Q0, Q1, Q2 and 1/2 octave on Q3, Q4, Q5).

If you tune past the band edges the ROM outputs a "1" on Q0, Q1 or Q2 depending on the channel spacing selected.
It also outputs a "1" on Q3, Q4 or Q5 when crossing the center of the selected band for 1/2 octave detection.

IC11 then selects which set of two outputs to use depending on channel spacing selected. (Q0 + Q3 or Q1 + Q4 or Q2 + Q5)

IC 11 also receives pulses to modulate the outputs into a pulse waveform.

Be aware that the ROM and IC11 are floating 6V above 0V rail!!! Pin 24 and 16 = 12V, pin 12 and 8 = 6V. These power rails often fail, so check them.

The three transistors perform level shifting to get back to CMOS voltages.

IC17 then uses the 1/2 octave bit to determine if the band edge detection is high edge or low edge and switch the logic to steer the correct pin (12 or 13).

IC 11 also receives pulses to modulate the output into a pulse waveform

For all tests keep pins 12 and 13 disconnected!!!!!!!!!!

[3pinplug]

Hi Peter
I disconnected pins 12& 13 as suggested and gained full control of correct frequencies on all bands tuned as low as 1.0MHz on low band and had 540 up on top band so looks like a band edge problem. Thanks for posting Peter so looks like this is the road to the fault! 👍

[frsimen]

Thank you Peter for your detailed explanation of the workings of the end stop circuits.

Mark,

There is a lot that can be checked armed with Peter’s explanation.

First a word of caution. Be careful when measuring around IC11 and the ROM (IC16), as a slip of the probe to 0V will likely cause damage.

As Peter has said, start by disconnecting the wires to pins 12 and 13 again and measure the voltages on IC16 pin 24 (12V), pin 12 (about 6.8V) and IC11 pin 16 (12V) and pin 8 (about 6.8V). If the 6.8V isn’t anywhere near right, check the circuit around Q20 before going any further.

The next thing to do is switch to range 5 and tune to 300MHz. We know that was working when everything was connected, so a first check can be made on the output from the ROM at that frequency.

Set the step switch to 50kHz per step. Measure and note the voltages on IC11 pins 2 and 14. They should be either 12V (call it HIGH) or something around 6V call it LOW (but may be lower).

What you do next depends on the measured voltages.
IC11 pins
Pin 2 Pin 14 Check IC11 pin (to see the ROM output in use)
LOW LOW 6
LOW HIGH 5
HIGH LOW 4

You should find that the IC11 pin that you have to check is LOW. If it isn’t try tuning to a lower frequency.

Next move across to IC11 pin 1. You should see a pulse waveform, although the pulses could be quite narrow.

Check the output pin of IC 11 (pin 7). It should be LOW, without any pulsing.

Check IC17 pin 8. It should be 12V.

Check test point TP11. That should be at 0V.

Check test point TP12. That should be 0V.
Check Terminal 17. That should be 12V
Check Terminal 12 That should be 12V
Check Terminal 13 That should be 12V.

Tune up to 400MHz. Check IC11 pin 4/5/6 that you checked previously. It should still be LOW.

Check test point TP12. That should be 12V.
Check Terminal 17. That should be 0V
Check Terminal 12 That should be 12V
Check Terminal 13 That should be 12V.

If all was well with the above, tune to the as high a frequency (530MHz+) as you can and check the output at TP11. You should measure 12V with pulses.

Carry out all the tests, even if something doesn’t give the expected result, as it will give a clue as to where a problem exists. Check for the presence of pulses at all the measuring points. You shouldn’t see any when the ROM output is low.

Sorry there are so many steps!

Paula

[3pinplug]

Hi Paula
Started wotking down tests, got the following;-
IC16 pin 24 = 12.33v
IC16 pin 12 = 6.84v
IC11 pin 16 = 12.34v
IC11 pin 8 = 6.83v
IC11 pin 2 = 5.98v
IC11 pin 14 = 11.11v
I am a bit stuck at the next bit with regard to what you do depends on the measured voltages, not sure what i need to do here could you give me a bit more info please?
Thanks
Mark

[frsimen]

Hello Mark

IC11 pins
Pin 2 Pin 14 Check IC11 pin (to see the ROM output in use)
LOW LOW 6
LOW HIGH 5
HIGH LOW 4

The formatting unfortunately got lost on the way, so it isn't clear what was intended.

You need to measure the voltages on pins 2 and 14 of IC11. Depending on what you see, you then check pin 6 or pin 5 or pin 4 of IC11. The HIGH voltage will be 12V, I'm not so sure exactly what the LOW will measure, but it will be a lot less than 12V.

If pins 2 and 14 are both LOW (6V or so) measure IC11 pin 6

Pin 2 LOW, Pin 14 HIGH (12V) measure IC11 pin 5

Pin 2 HIGH Pin 14 LOW measure IC11 pin 4.

The voltage on whichever pin you are checking (pin 4,5 or 6) should be around 6.8V or 12V.

IC 11 picks which input pin (4,5 or 6) to transmit to its output pin (pin 7) depending on the levels on its pins 2 and 14.

Paula

[3pinplug]

Thanks for the additional info will check this evening.

[3pinplug]

IC11 pins
Pin 2 = 5.99v
Pin 14 = 11.11v
Pin 4 = 12.28v
Pin 5 = 12.29v
Pin6 = 6.84v
Pin 7 = 9.67v and attach copy of trace as two lines appeared on screen, when i zoomed in i saw the following waveform see pic IC11 pin 7

IC11 Pin 1 = 8.89v and twin line waverform, see attached pic called IC11 Pin 1, out of ineterst what do you call this when referringf to it?

IC17 pin 8 = 6.69v
TP11 = 6.3v
TP12 = 0.00v

Terminal 17 = 0.04v
Terminal 12 = 12v on wire 0.00v on terminal as wore disconected
Terminal 13 = 12.16v on wire, 0.00v on terminal as wire disconnected

At 400mhz

IC11 pin 4 = 12.27v
Pin 5 = 12.27v
Pin 6 = 12.27v
TP12 = 0.00v
Terminal 17 = 0.00v
Termianl 12 = 12v on wire, 0.00v on terminal as wore disconnected
Terminal 13 = 12.16v on wire, 0.00v on terminal as disconnected.

At 544mhz
TP11 = 6.03v

Some of the pins, terminals and test points gave different figures to what was expected so hopefully these will help.