Re: Racal RA6790 Hang AGC problems
Peter, the circuit is a bit more then those few resistors. The
hang time and the decay time are separately controlled by
signals from the latches in 4042s U4 and U13, you need to check
that they are sending the correct control signals to the switching
transistors Q2 and Q19 and the 4066s U11 and U12.?? It looks to me
like something is not switching when it should.
I was sorting some 1792s recently that had AGC problems and found
sending a string of short CW pulses from a signal generator a
great help in fixing them.?
73 - Dan
ac6ao / g3ncr
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Racal RA6790 Hang AGC problems
Hi Everyone,
I have done an alignment on this receiver and it is working really well, but the only slight gripe I have is the hang AGC time constants. On the Long setting, it is incredibly long - at least 4 seconds, however Medium is so short that the AGC "pumps" noticeably on SSB signals.
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I thought it should be a simple matter to adjust some resistor values to something more useful, like maybe 1 second for Medium and 2 or 3 secs for long, but it is proving to be much more difficult than I thought.
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According to the manual, R45 (330K) on the A4 board sets the LONG time constant, and the parallel combination of R45 and R146 (27K) should set the MEDIUM time constant. I have changed R45 to 220K and it does seem to have shortened the long time constant, but changing R146 to a much higher value has no effect whatsoever on the medium time constant. In fact, removing the resistor altogether, still has no effect on the medium time constant?
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Does anyone have any information on what is going on here?
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Please note also, that I want to keep the "hang" AGC and not disable it as per the article by Dallas Lankford.
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Cheers,
Peter - VK2AN
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Re: Looking for Racal Knob
Google PRC320 knobs and tell if that¡¯s the same?
De Spence G5STO Sent while portable! please excuse typos.
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On 13 Feb 2025, at 22:27, M0XBO via groups.io <tweever@...> wrote:
? Guys,
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I¡¯m looking for a ¡°skirted¡± Racal knob similar to the one in the picture below. I think it has a 3mm (ish) spindle and is normally held by two tiny hex grub screws.
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Any help in tracking a spare one down or the manufacturer of the ¡°knob system¡± would be greatly appreciated.
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Many thanks?
?
David
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M0XBO
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Guys,
?
I¡¯m looking for a ¡°skirted¡± Racal knob similar to the one in the picture below. I think it has a 3mm (ish) spindle and is normally held by two tiny hex grub screws.
?
Any help in tracking a spare one down or the manufacturer of the ¡°knob system¡± would be greatly appreciated.
?
Many thanks?
?
David
?
M0XBO
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Hi all, I saw on that the AATU BCC540F and G can accept PWM data from the RT on a PRM 4790 and BCC39. But has anyone published the differences between these two models? Is G just later then F and perhaps more desirable because it is
more recent? Or are there some other differences to know about?
?
Thanks
?
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73 Eugene W2HX
My Youtube Channel:?
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Many thanks Rupert - Much appreciated!
Kind regards/73
Richard
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Richard & Dan,
I have had the RA1778 Chapter 25 paperwork scanned today and the resulting PDF is now uploaded to the Files area on this group.
73
Rupert
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Good afternoon All
Rupert, I think you are likely our only option to get hold of the missing pages. 2 other group members sent me really good copies of Part II after my request, just before Christmas, and both are missing the elusive Chapter 25
I am going to write to Colin Hinson (RAF Museum ex Hendon) but could be a long job as I know he has a backlog of stuff to archive.
I will be be happy to pay the? bill from the Copy Shop if you are able to get the pages scanned.?
As per prev post in the absence of a parts list, I foolishly guessed that the 1778 displays were same as the 1772 I don't have a 1772 so now looking for a use for them!!
For the time being, I'm up to date with the 1778's but I am going to be more careful in future!
I had some corroded wiring, mainly on the terminations of screened leads onto the IF boards,? which I thought might be caused by acidic flux. It was a real mess - the braid had more or less disintegrated. I managed to cut and re terminate but only just. When I was a broadcast engineer we used a lot of Hellerman sleeving and the Hellerine lubricant. I don't remember any problems even on old stuff so I think there must be some other treatment involved? The other mechanical issue was the foam rubber padding strips which had fallen to pieces! I'm still looking for some suitable material.
1792
I have a similar problem with schematics for the 1792.
Dan, I know you have a lot of experience with the 1792/6790 but so as not to complicate this thread, I'll write a separate note with all the details.
Essentially all the manuals I can find have got either parts of schematics missing or v poor definition.
I'm getting on quite well with my repairs but starting to get sore eyes after gazing at a really bad copy of the main IF board
cheers/73
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Richard
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Hello Dan.....and Richard, I have the RA1778 manual chapter 25 but only in paper form. If there are any parts which you'd like details of immediately then please let me know and I'll look them up for you. In the longer term, if nobody else comes?up with a soft copy of chapter 25 for you, then I can see if I can get the chapter scanned. It has 107 pages. My local Print Shop may be able to get them all scanned. 73 Rupert
I have a paper copy of the two volume 1778 maintenance manual which is
missing the Parts List which should be Chapter 25.? Does anyone have
this, as a pdf maybe?? The only on line version of Vol2 is also missing
this Chapter.? I am about to start again on the big wiring job on mine
where the Hellerman sleeves have decayed and thus ruined a lot of the
main wiring loom.
73 - Dan
ac6ao / g3ncr
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I have a paper copy of the two volume 1778 maintenance manual which is missing the Parts List which should be Chapter 25.? Does anyone have this, as a pdf maybe?? The only on line version of Vol2 is also missing this Chapter.? I am about to start again on the big wiring job on mine where the Hellerman sleeves have decayed and thus ruined a lot of the main wiring loom.
73 - Dan
ac6ao / g3ncr
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Update Parts List Displays
Good Afternoon All
?
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RA1778 Update
Thanks to help from group members I now have 3 x fully working RA1778.
This was my first experience of working on this unit and I enjoyed it more and more as I got to know my way round the rx. A lot more fun than the 1792!!!
The manual is easy to follow. TP values and scope traces are v useful.?
I thought it might be useful if I shared my experience because 2 of the faults were probably "generic"
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Transistor Spacer/Spreaders
I found a faulty 2N2369 in the 1MHz input amp on the Upper Loop board.
What was interesting is that the device appeared to have been stressed when the leads were pushed through the spacer/spreader of the type you find in units of this vintage causing the collector to go o/c. I've seen this before in Racal and Marconi units so I thought it was worth a mention!
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IF Amp Instability
I thought my repairs were complete but one morning, when I switched on my last "repaired" unit, there was was seemed like an agc fault (low if gain with agc stuck full on)? It was a very cold day - below freezing in the workshop and the fault cleared when room temp went up to normal.
It was defintely temperature sensitive and eventually I pinned it to the gain controlled amp ML1 in the main IF board taking off at a freq in the 2 - 3 MHz range.
Everything looked ok but additional decoupling of the supply rail close to the IC cured the problem. When I replaced the small decoupling cap (not the electrolytic)? C2 I found that it was OK but a lower value than shown in the schematic. This was the original cap which must have been there from new.?
Fitting the "right" value fixed it. It's hard to believe but I've seen a similar effect with 7800 series voltage regulators if they're not decoupled as per mfrs recommendations.? Again, maybe Something to look out for.
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Parts List
The manuals I have are excellent copies but I don't have a parts list which wasn't a problem until I needed to buy a couple of displays. I guessed it wrong (see below) so if anyone could help out with a parts list (or point me in the right direction) I would be v grateful.
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Displays for RA1772 and 1778
I guessed that the displays in the 1778 were the same as the 1772 .
I know better now but as I ordered the wrong part initially I now have 5 x? HP 5082-7300 as used in the 1772 which I would be happy to pass on to anyone who needs them for a small contribution! They weren't expensive.
The 5082-7340 displays used in the 1778 were much harder to find.
UK suppliers wanted a fortune but I found some genuine parts on the eBay US website (they don't show up on eBay UK) and persuaded the sellers to ship to UK.
I can provide details if anyone needs them. I have more than I need now so might be able to supply an odd one.
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Hope this helps
Best regards to all
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Richard
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Time to pass this radio along, I've taken it as far as I can.?When I got it it was non-functional. I replaced the following:
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EPROM sockets
RAM
Battery (new Varta)
Multiple IC's (all replaced IC's are now socketed - including the RAM)
Display lamps
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The radio is now functional and receives pretty well. It could probably use a complete alignment which I am not set up to do as I don't have a tracking generator per the instructions.
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Full disclosure - it does not pass BIT. It fails on all of the filter tests. I'm unsure if the circuit generating the signal, monitoring the signal or the filters themselves are bad. When I manually enter the filter settings everything works so I'm leaning more towards the circuitry vs the filters being the cause of not passing BIT.
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It has seven installed filters, LSB, USB, 400 hz, 1.2 khz, 3.24 khz, 6.8 khz and 16 khz
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Also there is one segment, lower left of the most Signiant digit, that is out and the silvering behind the LCD's is a bit discolored.
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The R-2174 tag says it is serial number 3188. The RA-6790/GM tag on the rear of the unit says it is serial number 3265.
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I have complete print outs of both manuals as well.
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$500 plus shipping or will meet within reasonable distance of zip 18974.
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Re: Racal RA6790GM in need of repair facility
On 2/3/2025 3:41 PM, Arnie Depascale wrote: Hello,? I'm new here.? I have and have had for many years a RA6790GM that for years has worked flawlessly.? A few weeks ago I could no longer program frequencies.? Everything lights up with Zero's and the fault light was lit. Sounds like a tantalum capacitor to me.? If you can check all the supply voltages and find one that's zero, then unplug boards one at a time you will find the culprit soon enough.? Favorites are the +/- 15V rails and the 20V rail into the A7 board which has a string of tants that can go one after the other, real annoying that is :^) 73 - Dan ac6ao
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Re: Racal RA6790GM in need of repair facility
You may have a power supply problem, if you have a shorted capacitor the receiver might act this way, I have attached a file that might help.
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Gary E Wingerd
RACAL retired
---------- Original Message ---------- From: "Arnie Depascale" <nelo44@...> To: [email protected]Subject: [RacalRadio] Racal RA6790GM in need of repair facility Date: Mon, 03 Feb 2025 15:41:09 -0800
Hello,? I'm new here.? I have and have had for many years a RA6790GM that for years has worked flawlessly.? A few weeks ago I could no longer program frequencies.? Everything lights up with Zero's and the fault light was lit.? I replaced the backup battery and the fault light is now off.? I did the reboot several times but still not operational.? The removed battery checked OK.
I'm located in Connecticut and wonder where I may find a repair facility..?
Arnie D.
K1NFE
nelo44@...
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Re: Racal RA6790GM in need of repair facility
Hi Arnie,
Did you try running the BITE initialization?
If not, just hold down the Lock button, then AM button, then release both buttons. If it finds a fault, take note of the code on the screen.
Cheers,
Peter - VK2AN
toggle quoted message
Show quoted text
Hello,? I'm new here.? I have and have had for many years a RA6790GM that for years has worked flawlessly.? A few weeks ago I could no longer program frequencies.? Everything lights up with Zero's and the fault light was lit.? I replaced the backup battery
and the fault light is now off.? I did the reboot several times but still not operational.? The removed battery checked OK.
I'm located in Connecticut and wonder where I may find a repair facility..?
Arnie D.
K1NFE
nelo44@...
|
Racal RA6790GM in need of repair facility
Hello,? I'm new here.? I have and have had for many years a RA6790GM that for years has worked flawlessly.? A few weeks ago I could no longer program frequencies.? Everything lights up with Zero's and the fault light was lit.? I replaced the backup battery and the fault light is now off.? I did the reboot several times but still not operational.? The removed battery checked OK.
I'm located in Connecticut and wonder where I may find a repair facility..?
Arnie D.
K1NFE
nelo44@...
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Re: RACAL PANTHER BCC715 BATTERY ELIMINATER
HI Dave,
Many thanks.
Jeff
On 29/01/2025 21:36 GMT g1jwg <g1jwg@...> wrote:
?
?
Hi Jeff
?
The BCC715 is a voltage conditioner/ regulator for the BCC70AT which is the BCC70 in a non manpack role.
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The BCC715 input is 12-18v with a nominal 13.5v regulated output
The BCC70AT input is 10-16v
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Regards
Dave g1jwg
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Re: RACAL PANTHER BCC715 BATTERY ELIMINATER
Hi Jeff
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The BCC715 is a voltage conditioner/ regulator for the BCC70AT which is the BCC70 in a non manpack role.
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The BCC715 input is 12-18v with a nominal 13.5v regulated output
The BCC70AT input is 10-16v
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Regards
Dave g1jwg
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Re: Racal Panther 10pin to Clansman 2pin 24v
A possible alternative perhaps??
I am sure this conversation is about the Panther V Radio... Testing into a Dummy load...Output can vary depending on frequency..
Just wish I could find out about power via the battery connectors. I don't want to be the guinea pig!
On Monday 27 January 2025 at 18:52:52 GMT, Stuart Mckinnon via <stuartjmckinnon= [email protected]> wrote:
I've learnt something today then
Stuart
On Monday, 27 January 2025 at 18:36:03 GMT, HT011 via <markwalton21= [email protected]> wrote:
Hi Stuart,
The other clue is the manual states in the 'clip in' config the 10 pin socket can be fed with 24v directly from the vehicle supply.
I would just love to know for sure regarding feeding it via the battery connectors incase it would damage something.
Cheers
Mark?
On Monday 27 January 2025 at 17:48:29 GMT, Stuart Mckinnon via <stuartjmckinnon= [email protected]> wrote:
Mark
I have a feeling Not, I am sure the VIU steps down the 24v that you feed it with to then supply the radio, thats of course why you have a Racal battery of around 12-14v, if? anyone can comment on my deductions ?
Cheers
Stuart
On Monday, 27 January 2025 at 13:19:43 GMT, HT011 via <markwalton21= [email protected]> wrote:
Hi Stuart,
I saw that I might have to rig up an adaptor.
Has anyone tried to power it with 24v via the battery socket? I have the power adaptors but would like some confirmation it won't break the radio and it will give the 20w output if powered this way via instead of the 10 pin.
Cheers
Mark
On Monday 27 January 2025 at 13:10:16 GMT, Stuart Mckinnon via <stuartjmckinnon= [email protected]> wrote:
Mark
This is the closest I can see on the bay??
G0TBI
On Monday, 27 January 2025 at 12:29:48 GMT, HT011 via <markwalton21= [email protected]> wrote:
Good afternoon,
?
Does anyone have a source of a Racal 10 pin (radio rear socket) to a 2pin Clansman style power input. To power the radio with 24v in the vehicle clip in mode.
?
Best regards
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Mark
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Re: Racal Panther 10pin to Clansman 2pin 24v
Just wish I could find out about power via the battery connectors. I don't want to be the guinea pig!
On Monday 27 January 2025 at 18:52:52 GMT, Stuart Mckinnon via groups.io <stuartjmckinnon@...> wrote:
I've learnt something today then
Stuart
Hi Stuart,
The other clue is the manual states in the 'clip in' config the 10 pin socket can be fed with 24v directly from the vehicle supply.
I would just love to know for sure regarding feeding it via the battery connectors incase it would damage something.
Cheers
Mark?
On Monday 27 January 2025 at 17:48:29 GMT, Stuart Mckinnon via groups.io <stuartjmckinnon@...> wrote:
Mark
I have a feeling Not, I am sure the VIU steps down the 24v that you feed it with to then supply the radio, thats of course why you have a Racal battery of around 12-14v, if? anyone can comment on my deductions ?
Cheers
Stuart
Hi Stuart,
I saw that I might have to rig up an adaptor.
Has anyone tried to power it with 24v via the battery socket? I have the power adaptors but would like some confirmation it won't break the radio and it will give the 20w output if powered this way via instead of the 10 pin.
Cheers
Mark
On Monday 27 January 2025 at 13:10:16 GMT, Stuart Mckinnon via groups.io <stuartjmckinnon@...> wrote:
Mark
This is the closest I can see on the bay??
G0TBI
Good afternoon,
?
Does anyone have a source of a Racal 10 pin (radio rear socket) to a 2pin Clansman style power input. To power the radio with 24v in the vehicle clip in mode.
?
Best regards
?
Mark
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Peter E
Spence G5STO
BILL KALOGERAKIS