Help needed with - Racal Dana 9081

[frsimen]

Hello Mark,

I think I’ve fallen foul of a documentation error.

Paragraph 4.64 of the service manual states that "on range 1 the half octave output at pin 17 is held in low condition by a positive level applied by the range switch on line RE, which via diode D14 turns off Q22.

Your measurement is the opposite of this, but the rest of the circuit description in the manual doesn’t give any help as to what to expect.

The circuit of the switch shows that on range 1 there is no 12V feed, but there is on ranges 2 –5. That matches what you have reported. There is no need to try the tests that I suggested, as you have now shown that the circuit beyond D14 is actually working as expected.

Looking at the operation of IC17, as described by Peter, that confirms that the description in 4.64 is wrong and the voltage that you are measuring at IC18 is correct.

All your measurements match the values (within one digit) that Peter has stated but the match is with the range 1 data rather than what it should be, the range 2-5 data.

I have included Peter's range 1 figures in parenthesis.

Pin 4 lower value is 0x4D ( 0x4E) and the upper is 0x62 (0x62)

Pin 5 Lower 0x3E (0x3D) Upper 0x4E ( 0x4E)

Pin 6 Lower not measured (0x33) Upper 0x41 (0x41)

Pin 7 0x53 (0x52)

Pin 8 0x42 (0x41)

Pin 9 0x37 (0x36).

You probably need to tune to a lower frequency to see the lower change point on pin 6.

I would measure the levels for a change of state at 4 when switched to range 1. Don't worry about the frequencies, just measure the pins 13 to 21 at the state change points. If they come out the same as you have measured already, that confirms that the ROM is faulty.

Paula

[frsimen]

Hello Mark,

I forgot one other point, which others have mentioned above. Do check that there is a solid connection between IC18 pin 10 and IC16 pin 21. That drifty voltage isn't right. It should be stable and very close to 0V on ranges 2-5 and 12V on range 1. It could be that when the meter is connected to measure the voltage on pin 21 of IC16 you can then tune up to higher frequencies. If that's the case, there is nothing wrong with the ROM.

Paula

[3pinplug]

Hi Paula
Heres the results:-
Pin 4 of Prom on band 1
Initially 12.30v then changes to 6.83v at 36.0mhz, only one change present on this band.

Pins 12.30v. 6.36v
13.0.00. 0.00
14.0.00. 12.31
15.12.31. 0.00
16.12.31. 0.00
17.12.31. 12.32
18.12.32. 12.32
19.0.00. 12.32
20.0.00. 0.00
21.12.32. 12.31
22.0.00. 0.00
23.0.00. 0.00

Checked connection between IC16 pin 10 & IC18 pin 10 using continuity test,allgood.
Also noticed that when i was switching band on the switch 1&5 caused the band switch to move internally as it appeared loose, tightened the nut up a little and this has resolved my missing / intermittent digits the display is 100% now with alldigits working.
One other thing i did at this point, heres the frequency coverage with 12&13 disconnected.
Band
1= 1-45mhz
2= 27-67mhz
3= 54-136mhz
4= 109-272mhz
5= 219-545mhz

With 12&13 connected i then get:-
1= 4.00-35.940mhz
2= 31.050-38.950mhz
3=62.000- 77.950mhz
4= 124.000-155.950mhz
5= 248.000-311.950mhz

If the prom is gone i have very kindly been offered one from a scrap unit i could try if it needs replacing.

[3pinplug]

Oh also with the meter on pin 21 of ic 16 i couldnt tune to the higher frequencies.

[frsimen]

Hello Mark,

The results show that the ROM either is ignoring the signal on pin 21 or that signal isn't pulling the input down as it should. The not quite 0V and changing reading on pin 21 is suspicious. I think now there is sufficient doubt about IC18 to warrant changing it. If that doesn't fix the problem, the ROM has failed.

The switch adjustment has produced a useful result, one thing less to worry about.

Paula

[3pinplug]

Hi Paula
Yes good news on the display, it didn't feel loose when turning it to select bands and if i hadn't got the covers off i would never have seen it moving, but useful fix to know.
Many thanks will swap out IC18 this evening.
Regards
Mark

[3pinplug]

Have changed out IC18 and now have display /bands as follows:-
1. 4.800 - 36.760mhz
2. 30.000 - 67.590mhz
3. 60.000 - 135.180mhz
4. 120.000- 270.360mhz
5. 240.000-540.755mhz
As part of checking i flicked the step up step down switch and the frequency jumped up by either 40 or 50 each time, even if i moved the channel spacing to 5 or 10. Is that how you use that setting. What checks should i do know to see if its all working?

[frsimen]

Hello Mark,

Is that the coverage now with the wires connected to pins 12 and 13 again? If it is, that's another fault ticked off the list.

Pressing the up or down toggle should change the frequency by the step size set on the step switch. From what you are saying, that isn't happening, but you need to check that you have set the controls correctly.

The settings are:

TUNE: SLOW
FINE TUNE: OFF.

Try a few different ranges and step sizes for your checks, to give a complete a picture of what is going on.

Paula

[3pinplug]

Hi Paula
Yes with pins 12 and 13 connected, ok will revisit the step switch and double check the settings and obtain some readings.

[3pinplug]

Readings as follows with tune slow & fine tune off

Band 1 set at ”10khz” band spacing and 4.800mhz
Flicking step up switch either once or twice for reading to change?
4.800 to 4.840 to 4.880 then flick step down get 4.840 to 4.800

Band 2 set at 10khz band spacing at 31.200
Flicking step switch up
31.200 to 31.210 to 31.220 flicking step down 31.210 to 31.200

Set at 25khz spacing and 39.000mhz
Flicking step up i get
39.000 to 39.025 to 39.050 flicking step down 39.025 to 39.000

Set at 60khz spacing and 374.520mhz
Flicking step up i get
374.520 to 374.640 to 374.760 to 374.880 flicking step down 374.760 to 374.640 to 374.520
Double what it should be

Then ran a test same frequency but either end of band spaing setting
30.000 in10khz steps
30.000to 30.040 to 30.080 to 30.120 same back down

30.000 in 60khz steps
30.000 to 30.060 to 30.20 to 30.180 same back down.

I have noticed that sometimes i have to flick the step up or down once for display to move but sometimes i have to flick it twice to move. I also no longer seem to have the ability to adjust to adjust to a desired frequency rolling in 0.001khz.
Hope the above points to another area.

[frsimen]

Hello Mark,

There does seem to be a problem on some ranges from what you are reporting, but I need a lot more results than you have given to work out where the issue lies.

The step sizes are governed by two sets of dividers. One is on the phase detector board and is used to switch between the basic step sizes of 2.5kHz, 3.125kHz and 3.75kHz at the phase detector. The VCO will be stepping 5kHz, 6.25kHz and 7.5kHz (only used in ΔF position) per single pulse from the UP/DOWN switch.

Band 5 uses the VCO output directly, so will one pulse per push of the up/down switch will step it by the step size.

Band 4 uses the VCO output divided by 2. So, to achieve a 5kHz/6.25kHz /7.5kHz steps, two pulses are needed for every push of the switch.

Band 3 uses the VCO output divided by 4 , so needs 4 pulses per push.

Band 2 uses the VCO output divided by 8 so needs 8 pulses per push.

On band 5, to achieve 10kHz steps, 2 pulses are issued per push with a 5kHz step size, 25kHz steps needs 4 pulses with a 6.25kHz step size and so on. The number of pulses on the other ranges is multiplied by the factor listed above.

On band 1, the band 4 VCO divider is used, so the band 1 and band 4 steps should be the same.

The multiple pulses per push are generated on the logic board, which is probably where the fault lies this time.

The ΔF position of the step size limits the number of pulses per push of the switch to 1. If you have selected 5kHz per step, you will be able to tune in 1kHz steps on ranges 2 and 3, but not 4 and 5. The minimum step on range 5 will be 5kHz.

Suggested Tests.

These only need to be done on one frequency per range.

1) Range 5. Select each of 5,10,20,6.25,12.5,25,50,15,30,60kHz per step. Check that is what you get. Check also that ΔF gives you 5kHz per step.

2) Range 4 Repeat for each of the above steps. Check also that ΔF gives you 2.5kHz per step. (you will see steps changing by 2 or 3kHz each time).

3) Range 3 Repeat for each of the above steps. Check also that ΔF gives you 1.25kHz per step (counts in 1kHz and occasionally 2kHz).

4) Range 2. Repeat for each of the above steps. Check also that ΔF gives you 1kHz per step (counts in 1kHz and occasionally needs 2 pushes for 1 step).

5) Range 1. Should behave the same as range 4.

Bearing in mind the loose range switch you found, check that the step switch doesn’t have same issue.

Paula

[3pinplug]

Hi Paula

Definitely something weird going on, please see results below and also recorded a few instances of what I have seen which I hope will help
Band 5
I will use yes for correct No for incorrect channel spacing and display scrolling
5khz step up fequency NO , frequency scroll NO
10khz step up fequency NO , frequency scroll NO
20Khz step up fequency NO , frequency scroll NO
6.25khz step up fequency NO , frequency scroll NO
12.5 step up fequency NO , frequency scroll NO
25 step up fequency NO , frequency scroll NO
50 step up fequency NO , frequency scroll NO
15 step up fequency NO , frequency scroll NO
30 step up fequency NO , frequency scroll NO
60 step up fequency NO , frequency scroll NO

Not working as ot should heres an example of what I am seeing:-
Frequency display shows 307.760mhz, channel spacing set at 20khz
307.760 to 307.780 to 307.760 to 307.780 to 307.860 to 307.840 to 307.920 Erratic 20khz spacing and randomly increasing / decreasing, saw this on other bands as well.

[3pinplug]

Band 4
5khz step up fequency NO , frequency scroll NO
10khz step up fequency NO , frequency scroll NO
20Khz step up fequency NO , frequency scroll NO
6.25khz step up fequency NO , frequency scroll NO
12.5 step up fequency NO , frequency scroll NO
25 step up fequency NO , frequency scroll NO
50 step up fequency YES , frequency scroll YES
15 step up fequency NO , frequency scroll NO
30 step up fequency NO , frequency scroll NO
60 step up fequency NO , frequency scroll NO

Again seeing steps up and down and inconsistent frequency spacing i.e this is what I saw:-

5khz is actually spaced 40khz
10khz is actually spaced 40khz
20khz is actually spaced 40khz
6.25khz is actually spaced 50khz
12.5khz is actually spaced 50khz
25khz is actually spaced 50khz
15khz is actually spaced 40khz
30khz is actually spaced 40khz
60khz is actually spaced 40khz

[3pinplug]

Band 3
5khz step up fequency NO , frequency scroll NO
10khz step up fequency NO , frequency scroll NO
20Khz step up fequency YES , frequency scroll YES
6.25khz step up fequency NO , frequency scroll NO
12.5 step up fequency NO , frequency scroll NO
25 step up fequency NO , frequency scroll NO
50 step up fequency YES , frequency scroll YES
15 step up fequency NO , frequency scroll NO
30 step up fequency YES , frequency scroll YES
60 step up fequency NO , frequency scroll NO

Band 2
5khz step up fequency NO , frequency scroll NO
10khz step up fequency YES , frequency scroll YES
20Khz step up fequency YES , frequency scroll YES
6.25khz step up fequency NO , frequency scroll NO
12.5 step up fequency NO , frequency scroll NO
25 step up fequency YES , frequency scroll YES
50 step up fequency YES , frequency scroll YES
15 step up fequency YES , frequency scroll YES
30 step up fequency YES , frequency scroll YES
60 step up fequency YES , frequency scroll YES

6.25khz is actually shoing and jumping 12.5 khz

BAND 1
5khz step up fequency NO , frequency scroll NO
10khz step up fequency NO , frequency scroll NO
20Khz step up fequency NO , frequency scroll NO
6.25khz step up fequency NO , frequency scroll NO
12.5 step up fequency NO , frequency scroll NO
25 step up fequency NO , frequency scroll NO
50 step up fequency NO , frequency scroll NO
15 step up fequency NO , frequency scroll NO
30 step up fequency NO , frequency scroll NO
60 step up fequency NO , frequency scroll NO

5khz is actually spaced 40khz
10khz is actually spaced 40khz
20khz is actually spaced 40khz
6.25khz is actually spaced 50khz
12.5khz is actually spaced 50khz
25khz is actually spaced 50khz
15khz is actually spaced 60khz
30khz is actually spaced 60khz
60khz is actually spaced 60khz

[frsimen]

Hello Mark,

Sorry to be a nuisance, but yes/no won't help to identify the trouble. Clearly it isn't working properly but it would be much better to know the exact steps that you are getting in each position. Armed with that, it will be possible to work out just which part of the circuit is the cause of the trouble.

The band 1 and band 4 results you have sent are what I'm looking for, if you can do the same for the other bands, that would be perfect.

The random jumping is a separate issue, which will need investigation.

There is one other check that you can make with your frequency counter. Hook it up to TP10 on the phase detector board and record the frequency there for each position of the step switch. Use range 4, although the range won't make any difference for this measurement. This will show whether there is a problem still on the Phase detector board, or if the problem is confined to the logic PCB.

Paula

[3pinplug]

Hi Paula
No problem on doing the tests,my error.
Band 5 results
Starts going up in 5khz, then jumps to plus 45khz steps, then goes down 35khz
Starts going up in 10khz, then jumps to plus 50khz steps,then goes down 30khz.
Starts going up in 20khz, then jumps to plus 60khz steps, then goes down 20khz.
Starts going up in 6.25khz, then jumps to plus 57khz,steps then goes down 43khz.
Starts going up in12.5khz then jumps to plus 63khz steps , then goes down in 37khz.
Starts going up in 25khz steps,then starts going down in 25khz steps, then up in 75khz steps.
50khz starts going up in 100khz steps, then down in 45khz before jumping up in 75khz steps.
Starts going up in 15khz steps,then starts going down 45khz steps, before jumping up in 75khz steps.
Starts going up in 30khz steps,then jumps up to 90 khz steps, then goes down in 30khz.
The 60khz range works in 130khz steps.
Frequency counter on TP10
Band 1 is 1.83mhz slowly increasing plus in frequency
Band 2 is 1.72mhz slowly increasing plus in frequency
Band 3 is 1.81mhz slowly increasing plus in frequency
Band 4 is 1.88mhz slowly increasing plus in frequency
Band 5 is 2.78mhz slowly increasing plus in frequency

[3pinplug]

Band 3
5khz goes up in 20khz steps
10khz goes up in 20khz steps
20khz goes up in 20khz steps
6.25khz goes up in 25khz steps
12.5khz goes up in25khz steps
25khz goes up in 25khz steps
50khz goes up in 50khz steps
15khz goes up in30khz steps
30khz goes up in 30khz steps
60khz goes up in 60khz steps

Band 2
5khz goes up in 10khz steps
10khz goes up in 10khz steps
20khz goes up in 20khz steps
6.25 khz goes up in 12.5khz steps
12.5khz goes up in 12.5khz steps
25khz goes up in 25khz steps
50khz goes up in 50khz steps
15khz goes up in 15khz steps
30khz goes up in 30khz steps
60khz goes up in 60khz steps

[3pinplug]

Hopefully the above is ok , if you need anymore measurement just let me know.

[CambridgeWorks]

If there were a UKVRR annual award for persistence, you guys really deserve it!
It is admirable to see such assistance offered and determination in fixing this. Shows just what this group is all about.
I would have binned it around page 2!
I have dealt with quite a few of the 9081/82 decades ago and don't recall anything as involved as in this repair.

My faulty sig gens I saw were either received here as just surplus gear or BER disposal.
HOWEVER, mine would have just failed and then been put to one side prior to disposal, or just no longer required. Usually a straightforward fix.

This makes me think that most of Paul's problems MAY have been caused by an ATTEMPTED repair that then introduced more new faults?
In my opinion, that makes things ten times more difficult to resolve.
Good luck guys, I admire your determination!
Sincerely, wishing you the best of luck,
Rob

[frsimen]

Hello Mark,

Thank you for the readings, they certainly aren't correct! The TP10 signal seems to be confusing your frequency counter, but I don't think there is anything wrong there.

The problem appears now to be on the Logic board. There is so much that is odd on range 5 that it's hard to know where to start on that.

On the other ranges, things are a little clearer. In the service manual, paragraph 4.26 has a table which shows the number of pulses for each range and channel step size. It appears that this generator is producing 16, 32 and 64 pulses correctly, which is why most of range 2 is working as it should. The 2,4 and 8 pulse settings seem to produce 16 pulses mostly. Band 5 is doing its own thing and isn't following this rule.

A few things to try. You don't seem to have tried the ΔF setting, which should force the pulse generator to produce only a single pulse on any range. Try that to see what happens.

There are three OR gates which are worth checking, as they are used to determine the divide ratios.

On the logic board, check the voltage on IC15 pin 1 and pin 2. There will be a setting where both are 0V, another where only pin 1 is 0v and a third where only pin 2 is 0V.

Check that when both pins 1 and 2 are 0V, the output on pin 3 is also 0V. When either pin 1 or pin 2 or both pins are 12V, the output on pin 3 should be 12V. All voltages, both on the inputs and output should be properly 0V and 12V, not drifting around.

Repeat for IC15 pins 12 and 13, checking the output on pin 11.
Repeat for IC 15 pins 8 and 9, checking the output on pin 10.

This check if some of the control lines feeding the pulse multiplier circuit are working.

When this was sold as not working, they weren't kidding, were they!

Paula