[Premium-Rx] Power Supplies - Careful

[David Schofield]

Hi,

I've used one of these to repair my WJ-8615 it seems to work 100% OK, 
and drops in without any modification of the metalwork / chassis.
I made up a set of adapter leads so that I could replace it with a 
correct supply should I ever be able to source one.
I also made up an adapter plate that allowed me to use the existing 
mounting holes.
It only consisted of a thin alloy plate cut to the same dimensions as 
the existing supply then mounting the replacement supply on it with 
counter sunk bolts.
I put some thermal paste on both the PSU side and the chassis side of 
the panel to ensure good heat transfer, but it runs stone cold, even 
with the fan off, although I tend to leave it on "just in case".

They do do a medical grade version, for nearly double the price, but I'm 
happy enough with this one at the moment, it has no measurable ripple 
Etc, and the Rx performance seems as good as ever.
I did try three times to rebuild the existing supply only to be met by 
smoke and flying components, so decided on the alternative method.

http://www.xppower.com/pdfs/SF_SDS60.pdf

Cheers,
Merry Christmas (almost),
Dave.S.







On 10/12/2014 22:53, Steve Pappin via Premium-Rx wrote:
> Switching Power Supplies Again - Be careful with substitutes and indications of failure!
>
> I cannot recommend installing substitute power supplies for a variety of reasons and it isn't fun to get a radio in that has been blown up due to a power supply failure.
>
> Substitutes: After testing a few power supplies I found the results to be less than desirable. That's why I have not been able to offer new replacements for the 8711 or 8615. I'm getting closer but I want to be able to offer drop in fully qualified replacements. The substitutes tested either run too hot, produce EMI splatter, or don't regulate properly. On top of that they lack the protection built into the original power supplies. Most do not have series pass regulators on the AUX outputs and this is a recipe for disaster. The output voltages can run dangerously high and the output ripple can exceed the original specifications. Your valuable radio can become a door stop. High output ripple = heat. High output voltages = dead solid state parts. The power supplies that are likely candidates are going to be expensive because they are medical grade.
>
> I have been collaborating with another engineer. He provided some great insight and caution regarding the power supplies that are used in our WJ radios. The linear supplies are solid and require little explanation. The switching power supplies were design specifically for the radios they went into. I'm briefly mentioning the 8711 but focusing on the 8615. I was consulting for the US Navy and we discovered an number of releases for the 8615 family (read below). In the end we refitted all of the radios with late model power supplies, filters, and fans. The components and designs improved with age. As capacitors improved output ripple dropped and new releases made use of better technologies. As we were repairing power supplies we discovered that the early capacitors had much higher ESR specifications, twice as high as today's parts, they ran hot. The result is high ripple current. As the capacitors age the ripple continues to increase and the capacitors in the radio are now bein
>   g subjected to that higher ripple. Tantalum capacitors don't like high ripple and as they age they also break down. As we have seen in many radios these capacitors eventually burn. When they do they leave a hole in the PC board and destroy all of the surrounding devices.
>
> WJ-8615: There were at least three different power supply, fan, and fan filter combinations. All were used in each release except for the final P version. The P version uses the CCI auto switched input, 85 to 264 VAC. They will all work in your radio but you must have the matching pieces. Each matching release will physically fit into the cavity with 0 clearance. The early power supplies were made by MACPOWER and late model power supplies were made by CCI.
>
> The fan filter is critical in this application. It removes noise generated by the fan and is connected across the +5V and -15V buses. The fan is rated at 24 VDC but runs at 20V in early models. In later models had the 796638 fan assy with series pass regulator for added noise suppression.
>
> Original D version components, mid release or field upgrade:
> 1) Fan Assy: 796638 - Toyo / WJ
> 2) Fan EMI filter: 796338 - WJ
> 3) Power Supply: 380408 - MACPOWER
>
> CCI still manufacturers the late model power supply but you must have matching pieces. The early 8615D fan filter is too tall and it will hit the top of the CCI power supply. The CCI power supplies are available new for $700.00 plus shipping. Dahlgren still uses them and they replace them instead of repair them.
>
> Best Regards,
> Steve
>
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