Help needed with - Racal Dana 9081

[3pinplug]

Hi all,
Just purchaed one of these which is in need of repair, when you switch it on the display lights up (has some segments missing) and does display diffeernt frequencies when you move the frequency selector, bu tthat is it. The Frequency wheel feels lik eiti is not attached and just spins and doesn;t change the frequency at all - is that normally how it feels?
Any ideas why the display is not moving at all, and also can I repair the missing segments?
The modulation side appears on the face of it to be working and I can set the meter from 0 -10 with some precision, whether it is giving an output I do not know as yet but it looks as though it may have on the face of it.
Attach pics of my unit with display shown it is fluctuating a little but i cant capture this in the pic.
I have seen a few posts on the Racal 9081 on here so there seems to be some very knowledgable people on this model about, hope you can help with some pointers.
thanks
Mark

[Station X]

I'm probably stating the bling obvious, but you have the control set to HOLD rather than FAST or SLOW. That will give the symptoms you describe.

Apologies if the picture is for "illustrative purposes".

[3pinplug]

Hi

No problem and sometimes the obvious thing is the answer, but no its the same wherever the switch is set to unfortunately. Wish is had been just that, that would have been great. But thanks for the comment much appreciated.
Regards
Mark

[Cruisin Marine]

I Haven't used one of these for many decades, but from memory the frequency whizzing change knob is optically coupled so there is no friction to be felt.
I believe the chips/sensors associated with this part of the unit may sometimes need replacing too. Also clean around the optical sensors of course.
The power supplies go bad too, so check all the voltage rails first of all, and of course look for the dreaded tants

[Station X]

Service manual is available here and probably from other places as well:-

https://elektrotanya.com/racal_9081_.../download.html

You may be able to get help from the Racal Dana group on groups.io.

My experience is with the 9087 and from what I remember I had to reseat boards, chips and displays to get all segments of the displays to work.

Synthesised signal generators are exceeding complicated beasts so you have to break them down into smaller blocks when fault finding. I found it useful to have a frequency counter to check the frequency at various points in the mixer chain and a logic probe to check for stuck lines.

Obviously check that all power supply voltages are present and correct.

Looks like you have a problem with the VFO or the pulses from the tuning control. A 'scope would be useful for checking those.

[3pinplug]

Hi Station X and Cruising Marine,
Thanks for the info and link to the manual, i will have a read and come up with s plan of attack. Will report back with plan and findings once I establish what board is where inside this thing, hopefully good layout etc in the manual.
Thanks again!

[FIXITNOW]

They do have Tant caps in these that go s/c

[3pinplug]

Hi Fix it now,
Many thanks will see if any tants in the display area, had a look at the service manual today but it seems to infer that the layouts etc are additional to the manual and you could get them from racal for an extra £10 back in the day. I will have a search and see if these come up anywhere, unless anyone has these and could post?

[Station X]

Originally Posted by 3pinplug

had a look at the service manual today but it seems to infer that the layouts etc are additional to the manual and you could get them from racal for an extra £10 back in the day. I will have a search and see if these come up anywhere, unless anyone has these and could post?

Try here:-

https://groups.io/g/RacalDana

[3pinplug]

Thanks station X!

Also i am right in recalling that you can replace tantalums with electrolytic capacitors instead?

[Station X]

That's what I do, but only if they're faulty.

[3pinplug]

Hi all
ventured insode just using visual inspection and smell and both led me to the following items on boards in the underside of the unit.
First one is a tant and resistor as soon as I took the shield plate off you could smell the burning! I cant find this board in the service manual, its marked by the arrow at the bottom of the photo showing the full undeside of unit.
I also found a +47 +16V tant that looks burnt and looks like it has something sticking out the side of it??, it bridges from post no.9 to ground, as it still has the values on, I can organise a replacement. This is shown in the board photo at approx 9pm position.

The board I am struggling with at the 6pm position, it does not seem to have the same naming convention as the ones in the manual, anyone know what this board is? I need to identify the two components to replace (C47 & R81) but unless I have missed them I can't see them in the manual.

[Cruisin Marine]

There is a 9081 and 9082 manual on this site (which has many superb manuals) http://www.g1sle.com/content/testgear

[Jon_G4MDC]

What sticks out of the side is a blob of Tantalum! They often do that.

[theredhouseinn]

Never switch on a vintage piece until you have done a visual of the internals. Check that the mains suppression cap(s) are not showing signs of stress, especially if they are of the Rifa make. Do a sample check of the R's and electrolytics to see if they are on the way out.
Then run it up slowly on the variac, meters and test sets connected, and pray.
John.

[frsimen]

Hello Mark,

The burnt out components are C46 and R81. They are on the FM loop assembly circuit, towards the top right hand part of the circuit diagram. They decouple the 24V supply to the IF filter.

C46 is 4.7 microfarads. A 35V volt or more component will suit.
R81 is 47 ohms.

Paula

[3pinplug]

Hi all
Thanks for the help, much appreciated. I only got time this morning to look at one side still need to run a visual on the other side and the boards at the front. One of you mentioned that the tants could be an issue, you weren’t wrong. Thanks for the componentvalues and board ref i will revisit the manual. Will post more pics if anything on the other biards comes to light, but the smell when i took the cover off indicated that something was not right!
Thanks again!

[3pinplug]

Finished my review of the boards and whilst I order the components I need I also found something that is certainly not helping the display, several pins with no solder Can only assume someone was working in there before and forgot to resolder them. On of the pins feeds all the other segments along one single track and is the starting point, so not being soldered on the first pin in a trail is certainly not a good thing!
Here's what I spotted straight away - see pic.

[Station X]

I had exactly that problem with my 9087, but it was just one lead that was not soldered and it had obviously not been soldered from new.

I'm not convinced that just changing components which are visually faulty will get this SG working. You may have to do some fault finding, starting by making sure that all power supply voltages are correct.

Did you ever establish whether the SG had any RF output at the frequencies indicated by the display?

[3pinplug]

Hi Graham
You may well be right there, but wanted to get any visual faults sorted before I go after it in anger. Will test the output etc once I fire it up after fitting the new components and see what is working etc to home in on those boards / supplies. Pleased with progress to date as these visual faults certainly won't be helping. Interesting you had a leg not soldered as well��