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Old 4th Oct 2018, 3:14 pm   #1
simonjp
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Default Racal RA1772 help

Hi

I recently acquired the 1772. The op said that it no longer worked. He had hardly used it.

I have a couple of questions.

I have the service manual.

The set appears muted in so far as there is no audio whatsoever, and after sticking a piece of wire into the ant jack, no signals either.

All voltages according to the onboard voltmeter seem normal.

I seem to have 68Mhz on the rear bnc instead of 34Mhz.

Should I assume that if any or all of the internal loops dont meet their respective conditions that the set defaults to a muted state?

It doesn't say anything in the manual. Maybe my question is too obvious.

Before I dig deep, I thought I would treat the radio to new filter caps, and get rid of as many tants as I can find.

But I have had a nasty surprise whilst trying to find suitable alternatives.

Each filter cap has a ripple current of between 7 and 8amps. I assume that they are long life too.
But even when searching for the first one which is 10,000uf at 16V ripple current 7.9A, the cost of such a beast is 10 upwards.

I anticipate that the ripple current marked on the cap is well above what is expected.

Does anyone have any personal experience of re-capping the racal?

Also, any leads to replacement slide switches that mount on the rear panel? They seem to have 25mm fixing centres.

Is there any experienced RACAL service engineers near to me ( Hailsham ) east sussex?
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Old 4th Oct 2018, 5:23 pm   #2
vosperd
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Default Re: Racal RA1772 help

I have a 1772 and it's running well on the original capacitors. I have not found it necessary to change any tantalum caps yet, although I've had to change one or two in my MA1720 driver.
The obvious thing to do is to sort out the 34 meg first.
I found that if the loops were wrong my set didn't go into mute mode but just got wrong indication of the frequency received. I have not had too many problems with mine I'm relieved to say.
I have had one or two problems with those slider switches. Mine were fixed with switch cleaner. They are available but not always easy to find.
Don
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Old 4th Oct 2018, 6:15 pm   #3
simonjp
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Default Re: Racal RA1772 help

Thanks Don, it would be great to just leave them in, they are date stamped 1975. My switches were seized, l used contact cleaner then wiggled them back and forth, next thing l knew the plastic shafts broke off both.

I have an ma1720 as well, got it last week from John, he has a few, it is in great shape.

I am going to try and link the 2 together so that they transceiver, as soon as I fix the ra1772 hopefully.
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Old 4th Oct 2018, 6:43 pm   #4
simonjp
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Default Re: Racal RA1772 help

oops, I've just realised that there is no pcb in the IF2 area.
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Old 5th Oct 2018, 9:26 am   #5
vosperd
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Default Re: Racal RA1772 help

That won't help!
I've been keeping an eye out but not seen anyone selling any RA1772 boards.

Don, m5aky
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Old 5th Oct 2018, 9:41 am   #6
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Default Re: Racal RA1772 help

Try HIFI SSB worth a shot .
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Old 5th Oct 2018, 9:56 am   #7
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Default Re: Racal RA1772 help

Telford Electronics some time ago got a load of 1772 remote control variants and I think they did their own front panels for them. Might be worth asking if they have any spare assemblies.

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Old 5th Oct 2018, 12:06 pm   #8
simonjp
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Default Re: Racal RA1772 help

Hi gents

Panic over.

Due to a total ignorance on my behalf and having not RTFM, and a lack of understanding of the layout, had a knee jerk reaction and assumed that the missing pcb was the issue.

The pcb was the isb pcb, so last night I spent much time reading about this new variant of dsb.

So without the isb/audio board is no problem.

After cleaning the mode switch and Mhz change switch and applying some nyogel 760 grease, the radio has sprung into life.

The speaker pops a bit but with cans on its fine.

Just need to get an understanding of filters now, which dont seem to do very much.

Anyway, considerable progress if a little egg on the face.


Thanks everyone.

Now I just need to get to the display logic and make an interface using a PIC and a look up table to drive the MA1720 in transceiver mode. ( winter project)
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Old 5th Oct 2018, 2:04 pm   #9
vosperd
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Default Re: Racal RA1772 help

Pleased to hear you have results.
It depends on what filters you have installed. On my set I have lsb,usb, bfo and am marked on the front panel. The filter selction is effective in usb and bfo modes only.
Don
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Old 5th Oct 2018, 2:08 pm   #10
deliverance
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Default Re: Racal RA1772 help

Good to hear it's up and running again a very good receiver .
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Old 6th Oct 2018, 10:36 am   #11
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Default Re: Racal RA1772 help

It will be interesting to see how you get it into transceive mode.
Do you intend to control the frequency from the receiver or driver?
Don, m5aky
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Old 6th Oct 2018, 9:54 pm   #12
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Default Re: Racal RA1772 help

If the 1772 and 1720 are working OK, just setting both to the same frequency will be near enough! The 1720 uses thumbwheels anyway.
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Old 7th Oct 2018, 8:14 am   #13
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Default Re: Racal RA1772 help

That's what I do. I hadn't thought of modifying my set up. I guess you wouldn't want to control a transceiver with thumbwheels, thinking about it.
Don
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