Help needed with - Racal Dana 9081

[3pinplug]

Hi all
Glad the retest of the voltages helped to home in.
I printed a copy of the component layout for the logic assembly board (19-0842) and can see R34,36,35 shown on the bottom right of the board, just above pin 30 and immediately below IC15.
Will check them (on this board) this evening unless I hear otherwise, thanks all for help in this area and post results once checked.

[frsimen]

Hello Mark,

The resistors that you have identified on the Logic board are indeed the ones to check.

Chris,

The 10-8-83 9081-9082 manual available from the Racal_Dana User group and other websites includes most of the diagrams. It is missing figs. 1-3 and one or two others, but at 171 pages is the best that I've found on line.


There is a link to the manual in post #85.


Paula

[PJL]

I won't interfere again! but there are a couple of further tests you could do before replacing IC15:
1. Disconnect Sz from pin 30 of the Logic board and check pin 2 measures 0 (looking for fault on other board).
2. Operate the Tune switch TC2 and check IC15 pin 1 changes state and pin 3 follows pin 1.

[3pinplug]

Hi Peter
I dont think Paula was saying that you were interferring, quite the opposite in fact. Your contributions to this thread have been fantastic so please continue to post as you have been. If anything its my lack of knowledge around this area that is probably frustrating but we all have to start somewhere and i have certainly been learning bits and pieces that i would otherwise have never known. So please see this through to the finish line its been a great team effort from everyone, with yourself being a key player in the team, so thanks again and i look forward to the day when we can say as a team “its done”!!!
With the amount of faults this will hopefully be a good post for the future for other new owners as i may win the award of “ most faulty 9081 ever” at this rate!

[3pinplug]

P.s looking at the unit in a bit Peter, so will cover the points you have raised then.

[3pinplug]

Hi all
Quick update as far as i can, checked the resistors and all three (R34,35 & 36) were all in tolerance. I disconnected pin 30 as per Peters suggestion and lost the 12v from IC15 pin 2, however i need to run this and the Ic 15 pin 1 & 3 tests with pin 30 disconnected again this evening as at this point i noticed another couple of wires had come of the rows of pins. This would have just happened when bending the board over as they definitely weren’t off the other day.

[frsimen]

Hello Mark,

While the wire is off terminal 30, check that the resistance from there to the chassis measures 10k ohms. It's worth removing the wires from Terminals 25 and 26 and measuring there too. That will allow you to prove that the resistors are connected as intended.

Paula

[3pinplug]

Hi Paula
Disconnected the wires and obtained the following values from pin to chassis:-
Pin 30 = 9.89k
Pin 25 = 9.89k
Pin 26 = 9.79k

Also Peter mentioned about some tests which i posted result of disconnecting pin 30, when he mentions TC2 is that the fine tune control as not sure what it is?

[frsimen]

Hello Mark,

All seems as it should be with the resistors

TC2 was a good spot by Peter, I'd missed that.

TC2 feeds in on terminal 24, feeds to IC10 pins 12 and 13. The output (pin 11) should be at the opposite state, (that is input 12V, output 0V or input 0V, output 12V. The level at IC15 pins 1, 8 and 13 should be the same as IC10 pin 11.

TC2 is the tune control switch. It's the one to the left of the tuning spin wheel, marked hold, slow,fast.

While in the area you might as well check the TC1 line. You can monitor on terminal 28 and you should find an inverted version on pin 6 of IC10. TC1 is also controlled by the tune control switch.

Paula

[PJL]

Originally Posted by 3pinplug

Hi Paula
Results as follows:-
Pin 2 IC15
5khz is 10.12v
6.25khz is 10.13v
12.5khz is 12.36v

We have now disconnected SZ and found the resistor (R36) is capable of pulling pin 2 to 0. Is SZ intentionally being pulled up by something or is this a fault on the other board?

This is NOT to exonerate IC15 as

Originally Posted by 3pinplug

Hi Paula
Checked IC15 pins as follows, certainly not as expected:-
Pin 1=0.00v no change of reading throughout each band & across each range.
Pin 2= 1236v , same state as above
Pin 3= 0.00v, same state as above

Says IC15 is broken as pin 3 should be '1' if pin 2 (or pin 1) is '1' so we maybe looking ahead at the next fault!

[3pinplug]

Hi Paula, Peter
IC10 Pin 12 = 12.37v
Pin 13 = 12.37v
Pin 11 = 0.00v

IC15
Pins 1,8,13 are same as pin 11 at 0.00v

Tried TC1 check when on slow i get 0.00v on pin 1 & 3, when i select fast both change to 12.15v. Waiting for a replacement IC 15 to arrive at present.

[frsimen]

Mark/Peter

I don't think there is anything untoward with those results, as far as they go. Moving the Tune control switch should change the voltage on pins 11,12 and 13 of IC10, so you will need to check that happens. There should be a position where the voltage levels swap.


The remaining mystery is where the 10V is coming from on pin 2 of IC15 when in the 5kHz position. 10V suggests a 2 diode drop, which could be a feed to the SZ line via the SX line. The SX line connects to the RP line via S2/2R on bands 1 and 4. The RP line goes to the phase detector board, but shouldn't connect to anywhere with a 12V feed on it.

A couple of suggestions to try.

1) Disconnect the wire from terminal 4 on the phase detector board. With 5kHz spacing and range 1 selected, what is the voltage on pin 2 of IC15 n the Logic board?

If it remains at 10-12V, reconnect the wire and try:

2) Disconnect the wires from terminals 9 and 10 on the phase detector board. Check the voltage on pin 2 of IC15 on the Logic board. If it is still 10-12V, reconnect the two wires.

If it is now 0V, measure the voltage on terminals 9 and 10 on the logic board. Note down what you find.

The above might identify where the unexpected voltage is coming from, but won't explain the cause of it.

Paula

[3pinplug]

1) Disconnect the wire from terminal 4 on the phase detector board. With 5kHz spacing and range 1 selected, what is the voltage on pin 2 of IC15 n the Logic board?
It is 9.31V with wire 4 disconnected.

If it remains at 10-12V, reconnect the wire and try:

2) Disconnect the wires from terminals 9 and 10 on the phase detector board. Check the voltage on pin 2 of IC15 on the Logic board. If it is still 10-12V, reconnect the two wires.
With wires from 9&10 disconnected Voltage drops to 3.60v

If it is now 0V, measure the voltage on terminals 9 and 10 on the logic board. Note down what you find.
With wires above still disconneceted i got:-
Pin 9 12.17v
Pin 10 6.07v
at the pins themselves.

Whilst talking about Pins labelled as 9 and 10 etc , if I quickly swap to the logic board pins 9&13, there is a resistor acros pins 9 to 13 and a 47uf (50v) electrolytic capacitor across pin 9 to ground track. See attached pic, showing where the neg lead of the electrolytic is connected to and also the resistor mentioned. Could these to have any effect on what we are seeing?

Next i tried the tune control, set switch to Int, fine tune led illuminates, tune set to slow position, Band 1, 5Khz channel spacing and display set to 32.000mhz exactly. As soon as i illuminate the LED lamp and move switch from off to INT the display goes haywire. i.e
it changes from 32.200 to 26.800ish, can't really see as the display apart from the begining no.2 showing as steady is scrolling really fast all over the place. If I move the larger of the tune controls to about halfway it changes the still scrolling frequency from approx 26.8 to 32.8mhz, then if i turn the control it to max the frequency falls back a bit down to 31.6mhz.
If i set the outer knob back to its lowest postion then turn the smaller fine tune adjustment it seems to move frequency at min from 26.8 to 25.8 when adjusted to max.

TC1 check
I cannot get an inverted trace, all i can see on the scope screen is the following:
Term 28 horizontal line on scope at 12v
IC10 Pin 6 horizontal line on scope at 12v

Thanks again all
Regards
Mark

[frsimen]

Hello Mark,

Thank you for the measured results. I was working from a less than perfectly clear printout of the circuit diagram last night and missed another path which will need to be disconnected. As well as the wires on terminals 9 and 10, the wire on terminal 8 on the phase detector board needs to be disconnected. There should then be 0V on pin 2 of IC15 on the logic board.

The voltage you have measured on terminal 9 on the phase detector board could be coming via R29 and terminal 4 and should disappear if the wire to terminal 4 is disconnected. There should then be 0V on terminal 8 too.

The voltage on terminal 10 is a mystery as there is no obvious path for anything there. R32 should pull the line low, so there must be a significant amount of leakage for you to measure 6V. However, 6.07v is suspiciously close to half of 12.17v that you measure on terminal 9. I think there is a short circuit between possibly terminal 11 and terminal 10 or terminal 8 and terminal 10. Terminals 8 and 11 should have 12V on them if terminal 9 has. If one of them measures 6V, there is a short circuit somewhere in the area between that terminal and terminal 10. Careful inspection of the terminals and the PCB tracks should reveal the cause.

The 10 ohm resistor makes no sense at all. Terminal 9 on the logic board is the +12V supply. The circuit shows R 63 10 ohm resistor and C30 a 47µF capacitor, but neither are connected to pin 13. Pin 13 is the up down tuning line. It’s clear from the photo that the resistor connects to pin 13 at one end but that is not in agreement with the circuit and I can’t understand what is going on here at all. The capacitor is a recent addition by the look of it.

I wouldn’t worry about the fine tuning problem for the moment, that’s a battle for later! Leave that control in the SLOW position, then it won’t cause any trouble for the present.
The TC1 line voltage (terminal 28 on the logic board) should be 12V in the fast and slow positions, but should drop to more like 2V in the hold position.
The TC2 line voltage (terminal 24 on the logic board) should be 12V in the slow and hold position and ought to drop to 0V in the fast position.

There seems to be quite a lot that isn’t right at the moment, the resistor connected to terminal 13 on the logic board is certainly a puzzle. Can you check for continuity on the logic board between TP8 and terminal 13. The circuit shows that they are connected. I wonder if they are on your PCB. If they are, that resistor really should not be connected to pin 13.

Paula

[3pinplug]

I was working from a less than perfectly clear printout of the circuit diagram last night and missed another path which will need to be disconnected. As well as the wires on terminals 9 and 10, the wire on terminal 8 on the phase detector board needs to be disconnected. There should then be 0V on pin 2 of IC15 on the logic board.

Yes - got 0.00v when the above was carried out


The voltage you have measured on terminal 9 on the phase detector board could be coming via R29 and terminal 4 and should disappear if the wire to terminal 4 is disconnected. There should then be 0V on terminal 8 too.

No still at 12v when term 4 disconnected.

The voltage on terminal 10 is a mystery as there is no obvious path for anything there. R32 should pull the line low, so there must be a significant amount of leakage for you to measure 6V. However, 6.07v is suspiciously close to half of 12.17v that you measure on terminal 9. I think there is a short circuit between possibly terminal 11 and terminal 10 or terminal 8 and terminal 10. Terminals 8 and 11 should have 12V on them if terminal 9 has. If one of them measures 6V, there is a short circuit somewhere in the area between that terminal and terminal 10. Careful inspection of the terminals and the PCB tracks should reveal the cause.

Nothing seen but will keep checking with my eye loupe.

The 10 ohm resistor makes no sense at all. Terminal 9 on the logic board is the +12V supply. The circuit shows R 63 10 ohm resistor and C30 a 47µF capacitor, but neither are connected to pin 13. Pin 13 is the up down tuning line. It’s clear from the photo that the resistor connects to pin 13 at one end but that is not in agreement with the circuit and I can’t understand what is going on here at all. The capacitor is a recent addition by the look of it.

Sort of have an answer for this see below explanation and accompanying pics.


I wouldn’t worry about the fine tuning problem for the moment, that’s a battle for later! Leave that control in the SLOW position, then it won’t cause any trouble for the present.
The TC1 line voltage (terminal 28 on the logic board) should be 12V in the fast and slow positions, but should drop to more like 2V in the hold position.
The TC2 line voltage (terminal 24 on the logic board) should be 12V in the slow and hold position and ought to drop to 0V in the fast position.

Can you check for continuity on the logic board between TP8 and terminal 13. The circuit shows that they are connected. I wonder if they are on your PCB. If they are, that resistor really should not be connected to pin 13.

No continuity - not connected.


Explanation regarding rogue resistor
If you look at the attached snip of the logic board layout and the photo of my board you will see the layouts are actually different, my board does not have R63 where it is shown on the Logic aasembly layout, also i attach a photo of the board number where it looks as if someone had indicated it is board revision 1 in marker pen?
Also, after more careful observation the rogue resistor does not actually connect to pin 13 i have an odd pin (not numbered) inserted in place in between pins 11 & 13 see photo. It is this isolated pin that the end of the resistor is connected too and not pin 13, however there is also a wire fitted to this end of the resistor and the un-numbered pin, i will attempt to trace where this wire goes off to. Could this resistor be R63 on my version 1 board, it was mentioned that there were 5 different manuals floating about , maybe the general circulation one does not cover this versionof the board.

Voltages for pins 8 - 11 on phase detector board with all wires connected:-

8 = 9.29v
9 = 9.91v
10 = 10.61v
11 = 12.01v

Hoe this helps.

Mark

[3pinplug]

Her the pics of the rogue pin withthe resiwstor and a wire attached - R63?

[frsimen]

Hello Mark,

At last the voltage on pin 2 of IC15 has dropped to 0V when it should.

Something is still wrong, as you should measure 0V on terminal 9 on the phase detector board with the wire to terminal 4 disconnected. The only place that 12V can come from is on the phase detector board. Have a good look around R27, R28, R29 , IC2 and IC6 for solder splashes etc. There has to be an unwanted connection somewhere in the area. A very long shot is that IC6 is faulty, but I don’t think that is very likely to cause this fault. Another possibility is contamination on the board, so a good clean up with a solvent cleaner in the area would may help.

The terminal 9 problem is probably related to the terminal 10 problem. Use your meter to check the resistance between terminals 8, 9, 10 and 11. Terminal 10 should measure an open circuit to the other three. The others should all measure 200k between them. You’ll need the wires off the terminals for this measurement to work, though.

TP8 should be connected to the real terminal 13, but not the additional terminal, which was originally thought to be terminal 13. The additional resistor and decoupling capacitor have been explained, so they aren’t causing any trouble.

There seems to be a leakage of a few kilohms to the 12V rail somewhere on the phase detector board. I’ve no idea what it could be caused by, but that is what is causing these odd voltage readings. That really needs to be sorted out, as the tuning steps will not work properly with things as they stand. Once that has been sorted out, and IC15 on the logic board has been changed there is a fighting chance that the step lengths may work rather better.

Paula

[frsimen]

Hello Mark,

Following another careful look at the circuit diagrams, I think you need to have a good check around IC6 pin 1 on the phase detector board, as that seems to be the source of the strange voltages. Follow the trace along its whole length. If you can't find anything, consider consider changing IC6.

Paula

[3pinplug]

Hi Paula
I have checked all round ic6 and ipa’d the board and cannot find any shorts rt c, also removed and checked the values of R28,27 and 29 all within spec.
I will change out IC6 but before i do i noted the current voltages on all the pins:-
Pin 1 = 12.04
2 = 12.33
3= 0.00
4= 0.00
5= 10.31
6= 12.31
7= 0.00
8 = 12.99
9= 10.61
10= 0.00
11= 4.13
12=0.00
13=0.00
14. 12.29
Thanks for the extra investigation whatever happened in the past it does seem to have affected a lot of IC’s.

[frsimen]

Hello Mark,

CMOS is fairly easily damaged by static discharges, so it's possible that some of this damage may have taken place during repair attempts in the past. I think that changing IC6 is sensible, let's hope it sorts out the odd voltage problems. It it is faulty, that could have caused some of the odd step sizes that were seen previously, although the faulty IC on the logic board will have a lot do to with that too.

Once the step sizes are working properly, we can attend to the problem with the fine tune circuits.

Paula