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Old 19th Feb 2023, 6:44 pm   #121
3pinplug
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Default Re: Help needed with - Racal Dana 9081

Hi Robinshack
Unfortunately only just seen your post, unfortunately i ordered all the IC’s this morning. Thank you so much for the very kind offer, that was really good of you and had i seen it earluer i would definitely have taken you up on your very kind offer.

Hi Motorbikeles
Yes you are indeed correct I am still trying to learn with my scope. Thanks for the suggestions as i say i am still learning so all info is gratefully received, with regard to the centre line i normally just turn scope on and set position of trace to center of crosshair, so with 5v amp/div selected when i have been measuring it does jump to 12v and i count 2.2 divs so 12. When you say ground scope for the 0v can i check what the procedure is fir this? Will look at beginning of trace next time and see the difference. Many thanks.

It is very interesting the logical process that Paula and Peter take with this they certainly know there stuff and its so good of them to give their time to help, i thought it was just as simple as replacing a few tants but its turned out to be a little more involved than thst, its great watching it slowly come together and hopefully once we get there it may also help others in the Future.
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Old 20th Feb 2023, 6:19 pm   #122
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Default Re: Help needed with - Racal Dana 9081

The input to the Y amplifier (Vertical deflection) normally has a switch, be it a slide switch, a lever switch, or push buttons which control the input. If you are using your scope to see DC voltages, as you are, the normal thing after switch on and allowing a period to settle down (especially with an older valved scope) is to set that switch to the ground position, place your trace to the 0v (centre line), then switch to DC. Sometimes it may suit better to set it to the lowest or highest lines, but for now, just use the centre.
If, instead of DC coupling, you were to set it to AC coupling position, you would get the same voltage deflection, but NOT referenced to that centre line.
If you were looking at a ripple on a high voltage smoothing capacitor, instead of 5v per division, you may need 100v per division, and the ripple would not easily be measured. However, by using AC coupling, you could set vertical to perhaps 1v per division. When you connect, the trace would fly up off screen, then slowly return to around the centre, but with the ripple clearly measurable with no dificulty.
Les.

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Old 21st Feb 2023, 8:41 pm   #123
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Default Re: Help needed with - Racal Dana 9081

Ho motorbikeles,
Thanks for the above will take this on board, on hold at mo as waiting for the replacement ic to arrive in the post!👍
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Old 24th Feb 2023, 11:44 pm   #124
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Default Re: Help needed with - Racal Dana 9081

I can furnish another complete logic/N–counter board from one of my spare project units if it beats you totally (foc), but I'd need your duff one in exchange so I've something to put back in mine afterwards, and I can persevere with the remains or use it to make a new one in my own time!

Can you confirm the number ("19–084x") of the board that's giving you all the mega–grief please?

I'll have a look in my spare unit tomorrow and see what mine has on position IC24 – there seems to be some uncertainty as to whether a '4002AE or a '4029AE is fitted, and I'm not 100% certain about the accuracy of the online manuals I have!

PS!

I've just had a careful look at the picture of IC24 the OP Mark posted, and the soldering looks "virgin" to me, so we can take it that the CD4002AE date code "645" is the original i.c. fitted me thinks!

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Old 25th Feb 2023, 11:10 am   #125
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Default Re: Help needed with - Racal Dana 9081

Hi all

UPDATE AT LAST! (been waiting on the parts)

Firstly, thank you Chris55000 for the very kind offer, you are a true gentleman! There are some really kind people on here and I couldn't have got here without all your help and kind offers, so again a big thankyou to you all - its greatly appreciated. I will park the board at present Chris if that's ok for the time being and see what the thoughts are following the progress I have just made after fitting the replacement CD4002BE.

Bad news first! The solder pad for pin 1 of IC24 (underside of pcb) came away when trying to remove the IC, have now fitted a holder and believe I have managed to get enough solder in the hole of the PTH and on the leg of the IC holder to make a joint. Checked topside of pcb with DVM probe on tip of ic holder underneath and touching pad on component side of PCB - I do have continuity. However I wanted to confirm where pin 1 of IC24 goes too, but when I look at the ciruit daiagram (as shown in attached pic) it doesn't seem to go anywhere - can anyone confirm where it goes too, I have looked and looked at the circuit diagram but can't see it - yes it probably has a big neon arrow pointing to it - saying "Pin 1 here" but i can't find it.

I have also disconnected (for the time being) the tant fitted in between IC23 and IC20 that doesn't show on schematic or on Paulas 9082, it was newly replaced but now shows sign of heat as the text has started melting, this poreviously smoked in front of me hence why I replaced it. Not sure if this is needed or not.

Now the more "positive news"!!!"!
I can now move the frequency display using the wheel and now have frequency displayed in the 5-32mhz range for the first time no more 0.000mhz displayed - HOORAY!"!"!!. I seem to have some dodgey digits that come and go but so pleased with this progress! Shown in the attachjed pics I seem to however stop at 311mhz and now can't seem to go any higher even when top range selected - should i reconnect that cap?

Please can you advise Paula, now that I have some frequency control what set of tests i should run now, also can confirm no bridged terminals present under IC6 as requested to check.

In the pics you will notice my plastic display selector doesn't match the frequency shown, it is just spinning and doesn;t seem connected to the knob, i need to take the knob off to see what is going on - does it just pull off, tried some gentle pressure on the knob as couldn;t see a grub screw and it didn;t move, so thought i would ask before going any further.

So pleased we have got this far have already had several celebratery cuppas!!

Regards

Mark
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Old 25th Feb 2023, 11:33 am   #126
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Default Re: Help needed with - Racal Dana 9081

Hello Mark,

That's really good news and you have some great progress at last.

You have three problems

1) Overheating tantalum capacitor - I thnk you can safely replace that with an ordinary electrolytic of the same value, the new one seems to have failed. Be certain that you have the polarity right, of course!

2) Pin 1 isn't connected to anything, that half of IC24 is unused, so it won't cause any trouble.

3) Not going above 311MHz.

For that you need to turn your attention back to IC13 and IC23. Check for pulses at IC23 pin 5 - if they are missing have a look back to IC13 pin 7, you may have a broken track.

Check that pins 6 and 11 of IC23 pulse between 0 and 12V when you try to tune above 311MHz. I suspect pin 11 doesn't, in which case, replace IC23.

If you see pulses there, check on pins 4 and 12 of IC25 If they are missing there, check for a broken track between IC23 and IC25. If all the pulses are present, there could be a problem with the ROM IC16

Paula
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Old 25th Feb 2023, 11:41 am   #127
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Default Re: Help needed with - Racal Dana 9081

Adding a little more information.

To check for the ROM we have to go full circle. Look for a pulse on terminal 13 on the phase detector board. Below 311MHz, you probably don't see anything. If you see a pulse when you try to tune above 311MHz, there is something wrong in the ROM or its associated circuitry. You could perhaps test for that first of all, as IC23 won't count properly if the end stop circuit is faulty.

Other checks to make are that the frequency steps match what you are expecting, so it increments/decrements in 5kHz/25kHz etc. steps as you have selected.

Finally, the knobs on the 9081 are collet knobs. There is a cap which comes off to reveal a nut which can be loosened to release the knob. Originally, the scale had a couple of pips which pressed into the knob, maybe they have broken off.

Paula
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Old 25th Feb 2023, 1:07 pm   #128
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Default Re: Help needed with - Racal Dana 9081

Thanks Paula & Peter, will conduct all the above this evening and report back.
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Old 25th Feb 2023, 2:35 pm   #129
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Default Re: Help needed with - Racal Dana 9081

That's some progress Mark.
As Paula said, the caps on the knobs are a press-in fit. A fingernail or thin blade will lift them enough to pull out.
The clear plastic printed disks were always pretty fragile.
I used clear bostik or plastic model makers glue to fix.
If all 4 tabs have broken off, it will still be fragile when glued back together.
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Old 25th Feb 2023, 6:57 pm   #130
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Default Re: Help needed with - Racal Dana 9081

IC24 in the easiest–to–get–at project '9082 is a '4002AE and the tantalum capacitor between IC20 and IC23 isn't present on mine!

I've got another paper '9082 Maintenance Manual that's written in a different type–face (Letter Gothic rather than the Century Gothic of the online ones) so it might have different layouts and circuits to the online ones, bit unfortunately I've buried it somewhere so I can't look at quickly I'm afraid!

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Old 25th Feb 2023, 7:28 pm   #131
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Default Re: Help needed with - Racal Dana 9081

Hi Robinshack & Chris 5500

I will prize the cap and post a pic of the printed disk once o get the knob off. The other manual may would be useful for me and others if anyway of getting it to pdf etc. Thanks for the heads up on the tant, will add an electrolytic as Pauls suggests when j get one. Right just going to set up and run the set of tests👍
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Old 26th Feb 2023, 1:32 pm   #132
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Default Re: Help needed with - Racal Dana 9081

Hello Mark,

On reflection, the upper frequency limit that you are seeing of 311MHz is close to what the VCO will be running at on the 5-32MHz band when set to its maximum frequency (my 9082 goes up to the 35MHz region on on its 32MHz range). You may find that by changing the step size, the maximum frequency you can achieve will vary. There may be a problem with the signal that indicates the 5-32MHz range has been selected.

To check if this is the cause, check the voltage on pin 8 of IC18. It should be 0V on the 5-32MHz range and 12V on all the others. If it is 0V all the time you may have a wire off between the switch and terminal 14 on the phase detector board. If it is changing as it should, move to pin 10 of IC18. There you should see 12V on the 5-32MHz range and 0V on the others. If you don't see that, IC 18 is faulty. If you do, check at pin 21 on IC16 for the same, in case there is a poor connection between IC18 and IC16.

Paula
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Old 26th Feb 2023, 4:11 pm   #133
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Default Re: Help needed with - Racal Dana 9081

Hi Paula, Peter
Results of tests as follows:-
IC23 pin 5 , +12v seen but no signal seen.
IC13 pin 7 +12v seen but no signal.
Will pop board out and look for broken track.
Pins 6,7 +12v no signal.
Pin 8 = 0v
Pin 9 +12v no signal
Pin 10 +12v and signal seen
Pin 11 =,Ov

Pin 8 IC18 0v on 5-32mhz range
12v on all others

Pin 10 IC18 12v on 5-32mhz range
0v on all others.

Pin 13PD board +12v when trying to increase frequency, drops to 0v when you try and decrease the frequency,

Based on results i will remove board and see if broken track as suggested , if not will change IC23.

The plastic selector disk has 3 of the 4 plastic lugs snapped off and these were on the inside of the knob still in the recesses there, will look at what options are for a fix as may have a thought on this.
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Old 26th Feb 2023, 5:41 pm   #134
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Default Re: Help needed with - Racal Dana 9081

Hello Mark,

Some of the results from your tests are as they should be. I should have said that you need to be spinning the tuning control clockwise to see any pulses on IC13 pin 7, IC23 pin 5 or on terminal 13 (the step down control line).

I'm not entirely clear which IC you were talking about with the measurements on pins 6,7,8,9,10 and 11. If it was IC23 having its outputs low is correct if IC13 never transmits any pulses to it. That could be a fault in IC13 or something that is blocking the count.

Perhaps the easiest thing to do is to disconnect the wire from terminal 13 on the phase detector board. and check whether you can then tune above 311MHz. If you can, the problem is with the band limit circuit. If you can't it's either IC13 or IC23. If no pulses come out of pin 7 of IC13 as you try to tune beyond 311MHz, it's IC13 that is faulty. If there are pulses and they are reaching IC23 but its outputs don't change, replace IC23.

What you have said about terminal 13 doesn't sound right. It should be high until you try to go out of range when it will drop low. I think you may have been measuring pin 16, the up/down line. Tuning down from 311MHz should leave terminal 13 at 12V.

Paula
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Old 26th Feb 2023, 6:21 pm   #135
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Default Re: Help needed with - Racal Dana 9081

Hi Paula
I will redo the IC23 pins 6-11 checks (thats the ic they were from) will spin wheel this time, will also conduct the ones above at the same time.
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Old 26th Feb 2023, 8:07 pm   #136
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Hi Paula, Peter

Hopefully i have this a bit better this time:-

IC23 Pin 5 - +12v no pulse when spinning wheel to increase frequency

IC13 Pin 7 +12v no pulse when spinning wheel to increase frequency

IC23 (spinning wheel to increase frequency)
Pin 6 = +12v no pulse
Pin 7 = +12v no pulse
Pin 8 = 0v no pulse
Pin 9 = +12V no pulse
Pin10 = jumps to +12v and pulse seen
Pin 11 = stays at 0v no pulse

IC25
Pin 4 = +12v no pulse
Pin12 = stays at 0V no pulse

Pin 13 still connected and with probe on it.
Scroll down frequency drops from +12v to 0v
Scroll up frequency before maxing out at 311mhz jumps from 0v to +12v
Hit max out and scroll up extra trace / pulse appears
Captured Pin 13's states in the attached / labelled pics.

Disconnected pin 13 couldn't get above the frequency of 311mhz. It did appear that whatever way i moved the wheel it went down in frequency?

Please advise form the above tests attachments.
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Old 26th Feb 2023, 8:52 pm   #137
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Default Re: Help needed with - Racal Dana 9081

Hello Mark,

I have to admit that I'm not sure what is going on at the moment. It seems that the end stop protection is coming into play, yet there is no good reason for it. I think your observation with pin 13 disconnected may be showing something significant.

When you hit the highest frequency, does it start counting backwards (turning the tuning clockwise), or does it jump to a lower frequency then continue counting up from that until it hits the end stop again?

If it jumps down then starts going up again, I would suspect IC13 which perhaps should be putting out a pulse on pin 7 at some point but isn't.

If it is counting down, that suggests that the end stop circuit is still connected somehow and driving the counter down. Check that the wire you have disconnected from terminal 13 on the Phase detector connects to terminal 15 on the logic board. If it's not the same wire, disconnect the wire on terminal 15 of the logic board and try again.

It's difficult to say at this stage whether this is a counter fault or an end stop circuit fault.

Paula
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Old 26th Feb 2023, 9:25 pm   #138
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Hi Paula
Will run the further tests and see what they show.
Regards
Mark
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Old 26th Feb 2023, 10:01 pm   #139
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Default Re: Help needed with - Racal Dana 9081

Quote:
Originally Posted by frsimen View Post

It's difficult to say at this stage whether this is a counter fault or an end stop circuit fault.

Paula
Disconnecting the "Step up" and "step down" wires from the Counter/divider board (wires on pins 12 and 13) will remove the band edge control from the equation.

Band edge detection reads the lines from the n-counter, compares them with data in the PROM, and outputs a signal for up, or down if the edges are crossed.
(It also uses data from band and channel spacing to give correct band edges).

This signal is then chopped into a square wave to give the pulses to steer the digital board in the correct direction.

I have reverse engineered the PROM data and produced some EPROM to PROM conversion boards to replace damaged PROMS with programmed EPROMS.

The PROM is vulnerable as it uses lower voltages, so its 0V is running at 6V. If Q20 fails short, the PROM dies.

Outputs switch between 6V (logic 0) and 12V (logic 1).
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Old 27th Feb 2023, 8:30 am   #140
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Hi Paula,Peter
Only had a little time this morning before work but with pin13 still disconnected i turned unit on with it still set to highest frequency scale, it went to 311.975 and stopped. I then started to turn the spinning wheel to increase the frequency and frequency started dropping. Continued spinning wheel upwards with display going the other way and dropping, at around 245mhz the display instantly blipped to 129mhz, then instantly blipped to 540mhz then went back to going down from 311mhz again? I ran out of time so will look in more detail at the other bits when i get in this evening.
Could this be related to IC23 as i previously did have the top band displaying, can’t be sure think we lost this when the wheel came into play - shall i change IC23 to eliminate it as it has no output?
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