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Old 18th Oct 2021, 10:32 am   #1
unixmanuk
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Default Clansman PRC320 Replacement Capacitors

Hi Guys - I'm looking to replace those troublesome tantalums in my PRC320 PSU and synthesizer unit. I know it's probably a well trodden path, but does can anyone suggest a good source they normally use to obtain the replacement capacitors for this job? (I've seen the various offerings from RS, CPC etc..) I'd also be interested to know what values have been used, since I have seen differing opinions on some sources.

Many thanks
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Old 18th Oct 2021, 3:28 pm   #2
Sparky67
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Default Re: Clansman PRC320 Replacement Capacitors

I am actually in the middle of doing this myself John on a couple of 320's, one faulty, and bought some axial caps for the job. They were selected to fit rather than their ESR and temp ratings - the PSU runs quite cool.

The 10uF 160V synth caps are working OK and C8 (2.2uF 160v) on the PSU 110V line is OK, but the cap I fitted at C6 (4.7uF 160V) I *think* may be causing the 110V supply to drop down to 60V-ish... Refitting the tant has brought the 110V rail back up. I now have a low ESR cap on order to try at C6. Slightly higher-uF value caps than the non-standard values originally fitted slow the lock time down a little, apparently.

A second PSU was found to have a couple of low gain transistors and I am looking at replacing a third device which appears to be faulty in use but not on the tester...!

I have also bought the LM2956 DC-DC converters and Nixie tube driver, plus associated filtering components, to rebuild the whole PSU as per the information on the PRC320 group on groups.io That looks a very viable long-term option as long as any remaining switching noise doesn't degrade performance. I will be taking S/N measurements at various freqs before and after fitting a rebuilt PSU to test that. Lock time is said to be almost instant.

Martin
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Last edited by Sparky67; 18th Oct 2021 at 3:40 pm.
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Old 18th Oct 2021, 4:15 pm   #3
unixmanuk
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Default Re: Clansman PRC320 Replacement Capacitors

Thanks for that, Martin.

Mine now has the characteristic "wobbles", so from what I can see, some or all of them will need to be done. The radial variants seem to be more easily available than the axial types.

On the videos, I have seen radial 10uF being fitted at the synthesizer, with axials fitted on the PSU unit 5 - if radials can be physically fitted there, then I will go down that route.

Interesting comment regarding the 110V rail - wonder if there is something else amiss there causing that on yours - Where are you sourcing your replacement capacitors from, Martin?
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Old 18th Oct 2021, 7:15 pm   #4
Sparky67
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Default Re: Clansman PRC320 Replacement Capacitors

John,

The original caps were sourced from Mouser and were being fitted to a working 320. The C6 replacement is from Bitsbox and will be two 10uF 100V LESR in series to see if that identifies the suspect ‘standard’ cap now in C6 as not being suitable in that position.

The other PSU failed on a set I bought which was tested as working but hadn’t been used for probably 5 years or more before that. It was being used to discharge a battery I was cycling, so was receiving for 12 hours plus each time. If i can’t get that board 5b running reliably a 5c and 5d will be built using the DC-DC boards mentioned previously.

Cheers,

Martin
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Old 19th Oct 2021, 8:36 pm   #5
Sparky67
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Default Re: Clansman PRC320 Replacement Capacitors

John,

The general purpose 85C 160V caps I have fit well and work fine in the synth and in the board 5b C8 position in the PSU. C6 was finally replaced with a single 4.7uF 160V cap from another source with an ESR of 3 Ohms and again fits well. I also changed a couple of transistors I wasn't happy with in the one PSU. Both are now working in their respective PRC320s, the Rx and Tx freq is quite stable.

I do have a spare set of these caps so will drop you a pm with more info.

Cheers,

Martin
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Old 20th Oct 2021, 9:06 am   #6
unixmanuk
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Default Re: Clansman PRC320 Replacement Capacitors

Thats great news, Martin.

Have just responded to your PM.

Regards,
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