Author Topic: [SOLVED] HP 6227B dual DC power supply - oscillation in master channel  (Read 2464 times)

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Offline bitseeker

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Re: [SOLVED] HP 6227B dual DC power supply - oscillation in master channel
« Reply #25 on: March 30, 2019, 04:41:33 am »
That's some really clean output. What an excellent outcome.

It's interesting that the 180µF caps reflect the usual capacitor miniaturization, but the 4000µF ones don't. The latter seem to be the same size as the original.

New axial caps look so much better in those axial locations. I'm glad you got them rather than "converting" to radials.
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Offline kj7e

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Re: [SOLVED] HP 6227B dual DC power supply - oscillation in master channel
« Reply #26 on: March 30, 2019, 06:26:18 am »
The hard part was to find caps BIG enough not to look goofy, so the higher working voltage parts increased the size some.

The supply works great, but gives off a considerable amount of heat from the capacitor bleed resistors. I'm considering changing out the 1k 5w resistors for 5k 5w.  I know this will effect some aspects of the specifications but I'm not a government lab.
« Last Edit: March 30, 2019, 07:39:30 am by kj7e »
 
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Offline bitseeker

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Re: [SOLVED] HP 6227B dual DC power supply - oscillation in master channel
« Reply #27 on: March 30, 2019, 07:27:15 am »
That sounds like a pragmatic solution. It's a new century. Don't waste power like it's 1999. ;D
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Offline Tomorokoshi

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Re: [SOLVED] HP 6227B dual DC power supply - oscillation in master channel
« Reply #28 on: March 30, 2019, 07:34:20 am »
...

I'm considering changing out the 1k 5w resistors for 5k 5w.  I know this will affect some aspects of the specifications but I'm not a government lab.

I replaced mine with either 5k or 10k. The only effect I see is when it's turned off, the needle does a little bounce on the way down.
 
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Online Sparky

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Re: [SOLVED] HP 6227B dual DC power supply - oscillation in master channel
« Reply #29 on: March 31, 2019, 12:19:53 pm »
Mine starts with serial # 2451A, all the caps have date codes from 1984, but I suspect it was made a bit later than that due to the rocker style power switch, however mine still has the course and fine pots, not the 10 turn pots the OP's has.  Sparky, what is your serial number?

Thanks for the detailed notes and repair report, kj7e!  (Sorry for the late reply -- I've been on travel away from my lab!)  I enjoyed to read about your progress, and the links to the replacement parts is great help for future!  I don't have a LCR meter so I can't measure the large capacitors --- I think might be time to get one!  ;D

The serial number on my unit is: 3314A-xxxxx

Great contribution to this thread!  :-+
 

Offline kj7e

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Re: [SOLVED] HP 6227B dual DC power supply - oscillation in master channel
« Reply #30 on: March 31, 2019, 02:38:38 pm »
Mine starts with serial # 2451A, all the caps have date codes from 1984, but I suspect it was made a bit later than that due to the rocker style power switch, however mine still has the course and fine pots, not the 10 turn pots the OP's has.  Sparky, what is your serial number?

Thanks for the detailed notes and repair report, kj7e!  (Sorry for the late reply -- I've been on travel away from my lab!)  I enjoyed to read about your progress, and the links to the replacement parts is great help for future!  I don't have a LCR meter so I can't measure the large capacitors --- I think might be time to get one!  ;D

The serial number on my unit is: 3314A-xxxxx

Great contribution to this thread!  :-+

Wow, yours is a very late model, after 1993.  Reading the manual, any year could have been ordered with the 10t pots.  I would suspect the rest of your caps are in good shape.
 
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Offline bitseeker

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Re: [SOLVED] HP 6227B dual DC power supply - oscillation in master channel
« Reply #31 on: March 31, 2019, 02:44:05 pm »
Wow, Sparky's is quite new. Although both your and Sparky's supplies have rocker switches, the badges and knob style also reflect the age difference.
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Online Sparky

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Re: [SOLVED] HP 6227B dual DC power supply - oscillation in master channel
« Reply #32 on: March 31, 2019, 05:46:56 pm »
Wow, yours is a very late model, after 1993.  Reading the manual, any year could have been ordered with the 10t pots.  I would suspect the rest of your caps are in good shape.

Oh, I did not know that!  How does one determine the date from the serial number?

And yes, I think you're right with the 10-turn pots -- I had same understanding from the manual that it was an option at time of order.  I'm not sure if HP decided to switch to 10-turn pots by default after sometime though.
 

Online Sparky

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Re: [SOLVED] HP 6227B dual DC power supply - oscillation in master channel
« Reply #33 on: March 31, 2019, 05:48:58 pm »
Wow, Sparky's is quite new. Although both your and Sparky's supplies have rocker switches, the badges and knob style also reflect the age difference.

I got lucky with my unit on eBay!  I did not know it was a newer or older one!

I don't mind the classic Black + Blue "hp" badge :D
 

Offline bitseeker

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Re: [SOLVED] HP 6227B dual DC power supply - oscillation in master channel
« Reply #34 on: April 01, 2019, 03:15:13 am »
The first two digits of the serial number, plus 60, is the year of the design that the unit is based on. It's not the year of manufacture, but will give you an idea of the oldest it could be. Date codes on components will then be able to give you a more accurate estimate of its year of manufacture.
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Re: [SOLVED] HP 6227B dual DC power supply - oscillation in master channel
« Reply #35 on: April 01, 2019, 05:55:23 pm »
The first two digits of the serial number, plus 60, is the year of the design that the unit is based on. It's not the year of manufacture, but will give you an idea of the oldest it could be. Date codes on components will then be able to give you a more accurate estimate of its year of manufacture.

Thanks!  That's good to know!  Next time I open it up I will look for date codes on few main components!  :-/O
 

Offline kj7e

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Re: [SOLVED] HP 6227B dual DC power supply - oscillation in master channel
« Reply #36 on: April 05, 2019, 05:17:36 am »
I changed out the 1K 5w bleeder resistors R76(A), R77(A) for 2.5K 5w parts.  Much better, rather than 2.5w of heat each, now down to 1w each.  They still get warm but you can put your finger on them now, before they would burn you.  Going to play with the VR3 bias resistors R75(A) some.  I have a feeling there is ample head room here and the bias current can be cut down some.

2.5K 5w resistors used;
https://www.digikey.com/product-detail/en/vishay-dale/ALSR052K500FE12/ALSR5F-2.5K-ND/257352



 
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Offline bitseeker

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Re: [SOLVED] HP 6227B dual DC power supply - oscillation in master channel
« Reply #37 on: April 05, 2019, 01:37:47 pm »
Cool. I still can't quite get over the size of those caps. ;D
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Offline kj7e

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Re: [SOLVED] HP 6227B dual DC power supply - oscillation in master channel
« Reply #38 on: April 07, 2019, 11:06:47 am »
Okay, found almost no change in VR3 (4.32v 1w zener) when changing the bias current limit resistors R75(A).  Stock 135 Ohm, 18v drop, ~133mA bias current, 2.4 watts gets the resistors very hot and the zener gets warm with almost 0.6w to dissipate.  Replaced them with 250 Ohm 5 watt, now 72mA bias current for 1.3 watts of dissipation, zener is a bit cooler dissipating 0.3 watts.  No problem with regulation, the zener voltage did drop from 4.25 to 4.18v.  The amount of heat out of the top of the supply is much improved.  I feel very comfortable leave this supply on all the time now.

« Last Edit: April 07, 2019, 12:51:57 pm by kj7e »
 
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Offline bitseeker

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Re: [SOLVED] HP 6227B dual DC power supply - oscillation in master channel
« Reply #39 on: April 07, 2019, 02:02:57 pm »
That's an excellent result. Thanks for documenting it (for when I get one of these :)).
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Online Sparky

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Re: [SOLVED] HP 6227B dual DC power supply - oscillation in master channel
« Reply #40 on: April 07, 2019, 03:13:34 pm »
Okay, found almost no change in VR3 (4.32v 1w zener) when changing the bias current limit resistors R75(A).  Stock 135 Ohm, 18v drop, ~133mA bias current, 2.4 watts gets the resistors very hot and the zener gets warm with almost 0.6w to dissipate.  Replaced them with 250 Ohm 5 watt, now 72mA bias current for 1.3 watts of dissipation, zener is a bit cooler dissipating 0.3 watts.  No problem with regulation, the zener voltage did drop from 4.25 to 4.18v.  The amount of heat out of the top of the supply is much improved.  I feel very comfortable leave this supply on all the time now.

Great update!  Thanks for this info!  I've been concerned about the heat...but I didn't look into what is required to reduce the heat output.  This is a great mod and I will definitely keep this in mind.  Not a bad idea at all to have it run a little cooler :)


That's an excellent result. Thanks for documenting it (for when I get one of these :)).
Ahhh yes, when not if;)  Am looking forward to your write up!  :D
 

Offline Jamieson

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Re: [SOLVED] HP 6227B dual DC power supply - oscillation in master channel
« Reply #41 on: April 28, 2019, 12:46:48 pm »
Thanks for documenting your experiences with the caps in this supply. I recently picked one up, serno 1607A, so ~1976. Works like a champ clean and quiet, a real gem of a supply. I love that the HP manual has full schematics and several pages describing in detail how each sub-circuit works. It's like a little textbook on PS design. Ah, vintage HP -- by engineers for engineers, marketing be damned!

 


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