Racal RA-6790GM/R2174 New to Me
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Hi Tom,
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I have just finished repairing an RA6790 and its a very nice receiver when its going!
I am no kind of expert on these but I can answer some of your questions. The battery in mine (and I assume yours) should be 2.4V. Just replace it with any NiCad battery pack with that voltage - many cordless phones have similar batteries, and you can just velcro it to the side of the case somewhere. Mine exhibited all sorts of strange behaviour till I replaced it - would start doing a BITE test then hang at some point.
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The bulbs on my display were all burnt out - I have now replaced all of the bulbs with green SMD LED's and 4K7 resistors - see photo attached.
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Two of the tantalums were shorted in mine - in the First mixer (A2) and had taken out a choke as well. I am not normally a fan of shotgun cap replacement but am now tossing up whether to replace all the rest - thoughts anyone? I noted that they were 20V tantalums running at 16V - not enough safety margin I would suggest.?
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The three transistors in A2 seem to run VERY hot! I added some additional heatsinking - not sure if its necessary but cant hurt.
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Yours sounds like it may have issues with the A6A2 board. replcae the battery first then go from there I would suggest. Hopefully you proms are not damaged.
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Cheers, and good luck!
Peter - VK2AN
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开云体育Hi Peter, ? Thank you for the suggestions. I have a couple hours today to work on it. So far found two open traces on the A6A2 board, repaired them but still have issues. I tested all of the traces as well as their connections to the front panel – everything seems intact now. ? I have a feeling that the A6A2 board will be replaced soon……… ? What serial number is your radio? Mine is 3265 on the Racal ID plate and 3198 on the R-2174 ID plate. ? Tom W3TA ? From: [email protected] <[email protected]> On Behalf Of Peter E via groups.io
Sent: Friday, November 29, 2024 10:14 PM To: [email protected] Subject: Re: [RacalRadio] Racal RA-6790GM/R2174 New to Me ? Hi Tom, ? I have just finished repairing an RA6790 and its a very nice receiver when its going! I am no kind of expert on these but I can answer some of your questions. The battery in mine (and I assume yours) should be 2.4V. Just replace it with any NiCad battery pack with that voltage - many cordless phones have similar batteries, and you can just velcro it to the side of the case somewhere. Mine exhibited all sorts of strange behaviour till I replaced it - would start doing a BITE test then hang at some point. ? The bulbs on my display were all burnt out - I have now replaced all of the bulbs with green SMD LED's and 4K7 resistors - see photo attached. ? Two of the tantalums were shorted in mine - in the First mixer (A2) and had taken out a choke as well. I am not normally a fan of shotgun cap replacement but am now tossing up whether to replace all the rest - thoughts anyone? I noted that they were 20V tantalums running at 16V - not enough safety margin I would suggest.? ? The three transistors in A2 seem to run VERY hot! I added some additional heatsinking - not sure if its necessary but cant hurt. ? Yours sounds like it may have issues with the A6A2 board. replcae the battery first then go from there I would suggest. Hopefully you proms are not damaged. ? Cheers, and good luck! Peter - VK2AN ? |
开云体育Peter, I will make one well intentioned criticism of your advice,
which was to use a NiCad battery, leakage from which has destroyed
a lot of A6A2 cards.? Use instead a NiMH replacement which are
much prone to leakage.? One used to be able to get a Varda
"Mempac" German made battery that was a direct drop in replacement
for the original.? If that can't be got any more a little daughter
card can be made to fit whatever is available.? I have used many
of these Vardas over the years with excellent results.? Looking at
my remaining stock recently showed they still have charge! I agree with the use of LEDs for edge lighting using the original boards, but a more even result can be got with four series connected strings of seven sideways firing LEDs with one series 100 Ohm R in each string.? Three wire links are needed, with slots cut in the existing traces for the LEDs, see attached pic. Assuming there has been battery leakage in the past with the original poster's CPU, the A6A2 board would have to be cleaned and examined very closely,? The leakage is alkaline and can be neutralised with some dilute vinegar followed by washing with isopropyl alcohol.? That nasty stuff gets everywhere with a fondness for destroying VIAs, creeping up transistor and IC leads and dissolving the copper inside the plastic body, getting into the 34 way connector next to the battery.? Any signs of dull grey solder or traces of blue near anything copper are bad news. A6A2 boards can be fixed if not too badly damaged, also new replacement boards are available. 73 - Dan ac6ao / g3ncr |
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Hi Tom.
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Mine appears to be a bit later than yours - Serial 5372 on both the front and rear plates - I wonder why yours are different?
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Dan is absolutely correct, I meant to say NiMh (not Nicad). Actually Nicads are quite hard to get now days, and I much prefer to have the battery pack wired to the board but in a separate location somewhere where leakage can't cause any grief.
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Cheers,
Peter - VK2AN |
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Hi Dan,
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Absolutely correct - I actually meant to say NiMh (must be getting old).
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I like your led lighting solution. I also wonder if it is possible to use that electroluminescent "string" that is available in various places? That would give really even illumination. I also like the idea that there are no more heat generating bulbs anywhere near the edge of the very hard to get LCD displays.
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Cheers,
Peter |
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Hi Dan,
I just looked up some info on electroluminescent wire. It needs to be driven with high frequency AC at a fairly high voltage. Not something you would want anywhere near a sensitive receiver I would think.
Cheers,
Peter
From: [email protected] <[email protected]> on behalf of Dan Rae via groups.io <danrae@...>
Sent: Sunday, 1 December 2024 9:37 AM To: [email protected] <[email protected]> Subject: Re: [RacalRadio] Racal RA-6790GM/R2174 New to Me ?
On 11/30/2024 1:27 PM, Peter E via groups.io wrote:
And of course I did mean less prone to leakage :^)? Even older.
Two things there, first there is not a lot of height between the existing board and the front panel, so not a lot of room for those strips.? Secondly you need the small surface mount LEDs that shine sideways to light the LCDs.? The original LED lighting on the GM needed a re-worked acrylic piece to accommodate the only LEDs that were available at the time. I've done a few like that, the only advice I'd give would be to buy some extra LEDs, since they have a habit of jumping off the board never to be seen again. 73 - Dan |
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Probably not, but I would think even 400Hz at high voltage would generate a fair few harmonics right inside a sensitive receiver.
From: [email protected] <[email protected]> on behalf of Peter Gottlieb via groups.io <hpnpilot@...>
Sent: Sunday, 1 December 2024 1:19 PM To: [email protected] <[email protected]> Subject: Re: [RacalRadio] Racal RA-6790GM/R2174 New to Me ?
Are the "string" wires different from regular electroluminscent panels?? Those
run at about 120 VAC 400 Hz which is pretty easy to create without much EMI. On 11/30/2024 9:15 PM, Peter E via groups.io wrote: > Hi Dan, > > I just looked up some info on electroluminescent wire. It needs to be driven > with high frequency AC at a fairly high voltage. Not something you would want > anywhere near a sensitive receiver I would think. > > Cheers, > Peter > -------------------------------------------------------------------------------- > *From:* [email protected] <[email protected]> on behalf of Dan Rae via > groups.io <danrae@...> > *Sent:* Sunday, 1 December 2024 9:37 AM > *To:* [email protected] <[email protected]> > *Subject:* Re: [RacalRadio] Racal RA-6790GM/R2174 New to Me > On 11/30/2024 1:27 PM, Peter E via groups.io wrote: >> Hi Dan, >> Absolutely correct - I actually meant to say NiMh (must be getting old). > And of course I did mean /less/ prone to leakage :^)? Even older. >> I like your led lighting solution. I also wonder if it is possible to use >> that electroluminescent "string" that is available in various places? That >> would give really even illumination > > Two things there, first there is not a lot of height between the existing > board and the front panel, so not a lot of room for those strips.? Secondly > you need the small surface mount LEDs that shine sideways to light the LCDs.? > The original LED lighting on the GM needed a re-worked acrylic piece to > accommodate the only LEDs that were available at the time. > > I've done a few like that, the only advice I'd give would be to buy some extra > LEDs, since they have a habit of jumping off the board never to be seen again. > > 73 - Dan > > |
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It may be possible but it makes it a pretty complex alternative to some simple LED's installed in place of the bulbs.
What would be really nice would be to remove the silver backing on the existing LCD's and replace that with EL panels?
Maybe a project for someone more adventurous than me....
From: [email protected] <[email protected]> on behalf of Peter Gottlieb via groups.io <hpnpilot@...>
Sent: Sunday, 1 December 2024 1:28 PM To: [email protected] <[email protected]> Subject: Re: [RacalRadio] Racal RA-6790GM/R2174 New to Me ?
EL backlighting is used in plenty of sensitive transceivers. Examples include
the Harris RF-350K and Tadiran PRC-2200. On 11/30/2024 9:25 PM, Peter E via groups.io wrote: > Probably not, but I would think even 400Hz at high voltage would generate a > fair few harmonics right inside a sensitive receiver. > -------------------------------------------------------------------------------- > *From:* [email protected] <[email protected]> on behalf of Peter > Gottlieb via groups.io <hpnpilot@...> > *Sent:* Sunday, 1 December 2024 1:19 PM > *To:* [email protected] <[email protected]> > *Subject:* Re: [RacalRadio] Racal RA-6790GM/R2174 New to Me > Are the "string" wires different from regular electroluminscent panels?? Those > run at about 120 VAC 400 Hz which is pretty easy to create without much EMI. > > > On 11/30/2024 9:15 PM, Peter E via groups.io wrote: > > Hi Dan, > > > > I just looked up some info on electroluminescent wire. It needs to be driven > > with high frequency AC at a fairly high voltage. Not something you would want > > anywhere near a sensitive receiver I would think. > > > > Cheers, > > Peter > > -------------------------------------------------------------------------------- > > *From:* [email protected] <[email protected]> on behalf of Dan Rae via > > groups.io <danrae@...> > > *Sent:* Sunday, 1 December 2024 9:37 AM > > *To:* [email protected] <[email protected]> > > *Subject:* Re: [RacalRadio] Racal RA-6790GM/R2174 New to Me > > On 11/30/2024 1:27 PM, Peter E via groups.io wrote: > >> Hi Dan, > >> Absolutely correct - I actually meant to say NiMh (must be getting old). > > And of course I did mean /less/ prone to leakage :^) Even older. > >> I like your led lighting solution. I also wonder if it is possible to use > >> that electroluminescent "string" that is available in various places? That > >> would give really even illumination > > > > Two things there, first there is not a lot of height between the existing > > board and the front panel, so not a lot of room for those strips.? Secondly > > you need the small surface mount LEDs that shine sideways to light the LCDs. > > The original LED lighting on the GM needed a re-worked acrylic piece to > > accommodate the only LEDs that were available at the time. > > > > I've done a few like that, the only advice I'd give would be to buy some extra > > LEDs, since they have a habit of jumping off the board never to be seen again. > > > > 73 - Dan > > > > > > > > > > > |
Peter E
