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Old 11th Aug 2017, 3:00 am   #1
Lavaldb
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Default RA 1772 power supply heat

My Canadian version (RA8772) heats so much that a fan is needed. One resistor shows 177 deg C.

Read about someone adding an aluminium heat sink bent to fit but cannot find the link to that post. I just wonder if anyone has experienced such a heat problem with the RA1772.

Thank you.
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Old 11th Aug 2017, 9:23 am   #2
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Default Re: Ra 1772 power supply heat

I recently had the transformer burn out on my RA1772. I hadn't notice the heat until this happened. I managed to get a replacement receiver and there is a fair bit of heat from the power supply. I keep an eye on it now and make sure there is plenty of air circulation around it. They advise removing the top cover if fitted in a cabinet.
Don, m5aky
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Old 14th Aug 2017, 7:56 pm   #3
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Default Re: RA 1772 power supply heat

When I restored my RA1778 some years ago I mounted it in the matching NATO case. This features a slotted grille over the rear heatsink which is just the right size to carry a small and quiet RS axial fan. Using this the heatsink temperature consistently stabilises at about 10 degrees over ambient and the external case temperature barely rises after several days of operation.

Every RA177x I've seen has more or less damage to the PSU interconnection wiring due to overheating. Amongst other things this leaches out the plasticizer in the wiring. The result can be a great deal of corrosion damage to the cableform.

The RA177x family are lovely receivers but I sometimes wonder who designed the PSU. Thermal considerations were clearly not uppermost in his or her mind.
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Old 15th Aug 2017, 9:37 pm   #4
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Default Re: RA 1772 power supply heat

This many Watts out of that space?
All your problem, perhaps?

Many have walked that road... Haunted? They must have been if they knew their stuff.

Maybe they did, maybe they didn't. I'm just guessing.
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Old 15th Aug 2017, 11:14 pm   #5
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Default Re: RA 1772 power supply heat

Maybe they weren't given enough space to do it in?

Competent designers can be forced into things they know will have repercussions.

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Old 16th Aug 2017, 7:38 pm   #6
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Default Re: RA 1772 power supply heat

+1e6
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Old 18th Aug 2017, 12:12 pm   #7
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Default Re: RA 1772 power supply heat

+1meg what? Nods?
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Old 18th Aug 2017, 1:22 pm   #8
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Default Re: RA 1772 power supply heat

I think that was a million calls of "hear hear" ...
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Old 19th Aug 2017, 12:25 am   #9
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Default Re: RA 1772 power supply heat

Is that text speak or a recent ham abbreviation?
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Old 19th Aug 2017, 10:57 am   #10
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Default Re: RA 1772 power supply heat

m0cemdave has got it exactly right.
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Old 14th Feb 2018, 2:27 pm   #11
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Default Re: RA 1772 power supply heat

Heat has, I suspect, caused the PSU to fail in my RA1772. Does anyone know if Telford Electronics is still handling the expert servicing of these lovely receivers? I have emailed them and not had a reply. Thanks for all help.
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Old 15th Feb 2018, 10:29 pm   #12
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Default Re: RA 1772 power supply heat

Stock faults on RA177x PSUs seem to be dry joints on the pass devices and also the large rectifier on the PCB. If the +12V regulator fails the other rails collapse, which can be confusing, so a good strategy is to make sure that one is working before addressing the others.

Changing the four reservoir capacitors, rewiring the PSU harness in PTFE cable and adding fan cooling to the rear heatsink always seems to be a good move with an RA177x if you're planning to keep it.

I didn't know that Telford Electronics ever serviced these but there are plenty of people around with a lot of experience in fixing them.
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Old 16th Feb 2018, 6:19 pm   #13
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Default Re: RA 1772 power supply heat

Quote:
Originally Posted by Lavaldb View Post
Read about someone adding an aluminium heat sink bent to fit but cannot find the link to that post. I just wonder if anyone has experienced such a heat problem with the RA1772.
Sounds like a ton of heat coming out there. How about a combination of mounting it on a heatsink and fitting in a small fan of the type used to cool CPUs? They come in different power outputs and run off just 12V. The larger ones are quite fiercely effective!
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Old 16th Feb 2018, 6:50 pm   #14
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Default Re: RA 1772 power supply heat

You may want to use a transformer to adjust the mains voltage to something which runs the regulators with a bit less voltage drop so the heat from them is no more than necessary.

Usually transformer windings are scaled to make enough overhead voltage for the worst-case mains input voltage and a set fully loaded with options like ISB.

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Old 16th Feb 2018, 10:11 pm   #15
GW4FRX
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Default Re: RA 1772 power supply heat

Quote:
You may want to use a transformer to adjust the mains voltage to something which runs the regulators with a bit less voltage drop so the heat from them is no more than necessary.
RA177x mains transformers are tapped at 10V intervals between 200 and 250V. In the vast majority of receivers I've come across, the tappings have been set to 230V. One of the first things I do prior to overhaul or repair is reset them to 250V. This still gives plenty of headroom on UK mains supplies and helps keep things cool.

Many RA177x transformers are mechanically noisy but seem to work quite happily. Parmeko transformers are generally worse than Partridges. Unfortunately they never seem to respond to attempts to tighten them up.
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Old 17th Feb 2018, 8:49 am   #16
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Default Re: RA 1772 power supply heat

I notice that the transformer on my replacement RA1772 is noisy but the set doesn't seem to be getting overheated at the moment. I'm still on the lookout for a spare transformer for the old one. I'm considering a rewind or getting one wound at some stage. I guess to make it a simpler job the 80V supply is not needed if I don't use RTTY.
On the working set the fault on the PLL has returned (local oscillator120K/cs low on the odd kc/s bands only) and this time it is on permanently. A couple of replacement boards would be handy but no-one seems to be breaking these sets for spares.
Don m5aky
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Old 17th Feb 2018, 9:57 am   #17
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Default Re: RA 1772 power supply heat

The sets are considered too good to break up. They get fixed instead, and they can be fixed. There are some fancy bits of test equipment where people with the knowledge to fix them at component level are too thin on the ground and you find those broken up. There are things with specialised and unique parts. If they fail, the remaining bits tend to migrate to Ebay as people try to recover some of their money.

The RA1772 is too good to break up. It's built out of what were standard parts at the time, The unique parts are the metalwork and the transformer. Transformers can be rewound. The OBIC LED digits may be the hardest parts to find. The receiver is overall, quite complicated, but it divides up into understandable sections. Added to this is a decent-quality service manual with diagnosis procedures as well as functional explanations.

So, the unavailability of spare boards for RA1772s is good. It's a result of them being fixable and worth fixing.

Best start a new thread, so that the forum structure stays neat.

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Old 17th Feb 2018, 1:27 pm   #18
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Default Re: RA 1772 power supply heat

Ooh, it gives me a shudder when I see fine bits of gear broken up (or "parted out")! Though I guess that those of us who haven't done it have probably come close to it from time to time, there's always the "I could have tried harder" and "parts worth more than the whole" guilt aspects.

With a previous widespread case of infuriatingly buzzing C-core transformers I used to encounter, an effective cure was to thread a long worm-drive hose clip around the offending core halves and tighten up for blissful silence, augmenting the original steel bands that had relaxed their grip. I'm not familiar with the RA1772 innards, but is the transformer thickly varnish-impregnated to make this approach nigh-on impossible?

I think if I ever owned one, I'd be looking to move as much of the heat-generating rectification and PSU componentry as sensible to the rear panel with a bit of metal-working to get as much additional radiating area as possible- with the proviso of "existing fittings and no butchery" that I like to stick to. Somehow, it seems ironic to be discussing the heat problems of semiconductor receivers when that was supposed to be the bug-bear of thermionic kit!

Oh, and there's a bit more guilt over all the NOS OBIC displays that I didn't rescue long ago in stores clearances before I was aware of the RA1772.... There's only so much "one day, maybe" stuff that can be hoarded!
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Old 18th Feb 2018, 2:16 pm   #19
RayEssex
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Default Re: RA 1772 power supply heat

Quote:
Originally Posted by GW4FRX View Post
Stock faults on RA177x PSUs seem to be dry joints on the pass devices and also the large rectifier on the PCB. If the +12V regulator fails the other rails collapse, which can be confusing, so a good strategy is to make sure that one is working before addressing the others.

Changing the four reservoir capacitors, rewiring the PSU harness in PTFE cable and adding fan cooling to the rear heatsink always seems to be a good move with an RA177x if you're planning to keep it.

I didn't know that Telford Electronics ever serviced these but there are plenty of people around with a lot of experience in fixing them.
GW4FRX, thanks for that reply. Telford will look at my set, but I am in East Anglia and they are in... Telford. Long way to travel... isn't there anyone closer
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Old 18th Feb 2018, 3:27 pm   #20
Herald1360
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Default Re: RA 1772 power supply heat

You could try a request here:

https://www.vintage-radio.net/forum/...play.php?f=145
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