Help needed with - Racal Dana 9081

[Chris55000]

I would definitely replace IC23 as there's something strange still going on with the N counter chain somewhere!

There isn't a pin got folded under an i.c. following a previous replacement is there? – I used to be always getting caught out by that one by the colleague at our fleapit who checks out our warranty returns, and it's an easy mistake to make!

One of those little hand–held portable Chinese Digital IC testers helps when you're got a lot of logic and gating faults on ordinary TTL and CMOS but the price of the things has risen alarmingly towards three figures of late!

Chris Williams

[frsimen]

I agree that IC23 could be faulty, but it won't do any counting if it isn't sent some pulses to count by IC13. Tests so far have not shown any activity on IC13 pin 7, so perhaps IC13 is faulty rather than/as well as IC23.

Mark,

The most recent observations are best described as odd and seem to suggest that the end stop circuit is forcing the count down. Follow Peter's advice to disable the end stop circuitry. If the counts are still all over the place monitor the up/down line on pin 10 of IC23 or IC13 to see if that is changing up and down. It should stay high all the time the tuning control is turned clockwise, low for anticlockwise..

Chris is right in that there is something odd in the N counter, quite what or where is difficult to pin down from what has been seen so far. With the end stop circuitry disabled, hopefully the N counter will behave more sensibly and it will be possible to make a better assessment of where the trouble lies.

Look for pulses at the output of IC13 (pin 7). If you see them, you should see IC23 pin 6 change state with every pulse from IC13 and IC23 pin 11 change with every other pulse from pin 13. If you never see a pulse from IC13 pin 7, check for pulses going into IC13 pin 5. You will only see pulses when you are turning the tuning knob, of course.

Paula

[3pinplug]

Hi Paula
When conducting the above tests should i leave pin 13 still disconnected on the logic board or reconnect it for these?

[3pinplug]

Peter is saying to disconnect pins 12 and 13, so 13 is the one i already have disconnected on the 18-0842 board logic Assy?

[frsimen]

Hello Mark,

The idea is to isolate the end stop circuit, so you need to disconnect both pins 12 and 13 on the phase detector board.. That should allow whatever is wrong to be identified more easily.

Paula

[Chris55000]

. . .I've not powered up my latest '9082 yet but from the seller's description it certainly seems there's a very similar nonsense going on to what the OP is experiencing (altho' mine's a '9082 I'm expecting similar pulse sequences to those explained by Peter and Paula!) – I'll get it down, have a prod round and report my findings, and will be paying particular attention to the step–up/step–down pulses on pins 12/13 of the P.D. board!

Chris Williams

[3pinplug]

Hi
Just noticed a solder bridge across pins 6&7 on IC8 on the “19-0842” logic board, will check to see if thats right, before conducting the other tests. Will isolate the pins , thanks Paula.

[frsimen]

Pins 6 and 7 of IC8 on the logic board should be connected together, so that's nothing to worry about!

Paula

[3pinplug]

Thanks, it just caught my eye as someone has wielded an iron on those two pins when compared to the rest. Will run the tests this evening and post results.

[3pinplug]

Hi Paula, Peter & Chris
Heres the latest results:-
Disconnected pins 12&13 from the det assy (18-0846) board.
This expanded the frequency display again to fixed display on each band as follows:-
0.000
59.395
135.719
373.437
545.797
However disconnecting pins 12/13 also appears on the face of it to have disconnected the spin wheel function.

Pin 10 IC23 goes high clockwise , low anticlockwise.

Pin 10 IC13 goes high clockwise, low anticlockwise

IC13 pin 7 +12v no pulse

IC23 pin 6 0v no pulse

IC23 pin 11 +12v no pulse

IC13 pin 5 +12v and pulsing!

Regards

Mark

[3pinplug]

Need to add, by disconnecting the spin wheel i mean frequency display shown doesn’t change, but rotating clockwise etc does move the trace.

[frsimen]

Hello Mark,

The 0.000 output on range 1 is because the VCO is running much too high in frequency, so that isn't a new fault.

If IC13 isn't sending out pulses, it's possible that the VCO is now stuck out of range and can't count down as IC23 has got a count which can't be changed.

I think the best thing at this stage is to change IC13. Leave the wires to pins 12 and 13 disconnected for now. Hopefully, tuning will be under your control again with a new IC13. If not, replace the wires on pins 12 and 13 to see if that helps. It may be that IC23 is faulty too, but I can't say for sure until you have replaced IC13.

Paula

[CambridgeWorks]

With all the faulty components, I wonder if a supply rail has in the past had a catastrophic voltage surge?
At my last job, we had a complex VHF/ UHF transceiver returned for repair. No fault description with it whatsoever. Maybe just "u/s"?. I spent many hours gradually repairing it section by section. On the final day, It was ready for a full specification test sheet to be completed.
Near the end, it failed as having no wideband audio available at the facilities connector on rear panel.
The fault tracing revealed one line o/c between line remote module and rear d socket.
This entailed removing the main chassis interconnect circuit board, quite a task.

All was revealed. Molten copper and black stains around the area where a PCB track had been vapourised. Turned out, it had suffered a near miss lightning strike!
If only I had been informed before starting the complex faultfinding and repair!
Rob

[3pinplug]

Hi Paula
Many thanks, i will start extracting IC13, great call to get the spare IC’s as have them sitting here ready and waiting.

[3pinplug]

Hi Rob,
Thats sounds a nightmare repair! Yes certainly several IC’s may have been affected but with everyones help its come along way.

[Cruisin Marine]

Originally Posted by robinshack

With all the faulty components, I wonder if a supply rail has in the past had a catastrophic voltage surge?
At my last job, we had a complex VHF/ UHF transceiver returned for repair. No fault description with it whatsoever. Maybe just "u/s"?. I spent many hours gradually repairing it section by section. On the final day, It was ready for a full specification test sheet to be completed.
Near the end, it failed as having no wideband audio available at the facilities connector on rear panel.
The fault tracing revealed one line o/c between line remote module and rear d socket.
This entailed removing the main chassis interconnect circuit board, quite a task.

All was revealed. Molten copper and black stains around the area where a PCB track had been vapourised. Turned out, it had suffered a near miss lightning strike!
If only I had been informed before starting the complex faultfinding and repair!
Rob

I once went to site and was confronted with a molten mess after a lightning hit! I stood in both shock and awe at the immense power of nature when it gets angry.

[Chris55000]

. . .And yet these days, certainly in Walsall where I live, there's been no lightning whatsoever this year, only one or two flashes on the odd day in 2022 when a thunderstorm passed nearby, and I don't remember any in 2021 either, but it only needs one strike nearby, whether to a TV aerial or via the mains distribution network to get near any electronics to cause irreparable damage!

Lightning does, after all, come from a source which may be 20–50 C (coulombs), an absolutely enormous quantity of electric charge, equivalent to a voltage potential of 200–400 kV above earth, and the current in the return–stroke has a peak rate of current rise (di/dt) that may be anything from 10 kA/μs to 50 kA/μs, so even a minute fraction of a microhenry inductance in a conductor, when hit by lightning, is enough to develop absolutely enormous voltages in it!

Chris Williams

[CambridgeWorks]

Mark, back at the beginning you had the occasional strange voltages around the regulators. From memory, a bit awkward to get at with wires all over and no sleeves over the connection? Also, some ic you have are the early 4000AE series without diode protection. I think you had suspicion that someone had worked on it before?
I am thinking maybe during previous attempts someone may have shorted a different voltage to a supply rail around the regulators?
Are the ics you are finding faulty all AE?
I have a 9081/2 original manual somewhere, but not seen it lately, it got moved? So, would like to find it in case I made any notes to put with it.
Rob

[karesz*]

Gentlemen,
I think with old 4xxx CMOS it would be valuable to place transient absorbers (and latch-up protection between relevant voltages) on the supplies__and use an antistatic workbench...
K.

[3pinplug]

Hi all

Have changed out IC13 and stil have no output on pin7, as I now have a number of IC's at my disposal I tried 2 x CD4029AE and 1 x CD4029B chips in there and ALL have the same characteristic i.e no output on IC13 Pin 7. I have pulses on IC13 pin 5 but no output from what I can see on pin 7.

IC13 pin 5 pulses observed when spinning wheel both clockwise and anticlockwise and the frequency is moving up and down.

IC23 Pin 10 - high when spinning wheel clockwise, low when spinning anticlockwise.

IC13 pin 10 - high when spinning wheel clockwose, goes low when spinning anticlockwise.

The frequency display (first range) still just shows 0.00 - no change when wheel spun.


The remainder of frequencies shoot high when first slected then after spinning the wheel anticlockwise will start to go down as follows:-


Frequency (2nd selection) shoots to 57.575 when first selcted then after while when spinning wheel anticlockwise frequency starts to scroll down to 27mhz then all digits just start flashing and are not that readable.

Next band jumps to 135.599 when selected, then again after turning wheel for a bit starts to move down band to 54mhz then all digits flicker / go mad - same as above condition.

Top band goes to 545.054 then again after turning wheel for a bit goes down to 130.150mhz and then all digits go mad again.

With no output on pin 7 of IC23 should i change out IC23?

Regards

Mark