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Author Topic: Kenwood PS-30 Power Supply Excessive Voltage Issue  (Read 12814 times)
W5JDF
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Posts: 8




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« on: May 10, 2012, 09:02:35 PM »

I bought a used PS-30 Power Supply (cheap now I know why...hihi).  When I got it I had no DC output.  I checked all the fuses and foud that the 20A internal fuse was blown.  I have replaced that fuse and now have DC output, but it is around 21-22VDC with no load.  The manual specs are 16VDC.  I tried adjusting VR-1 but it has no effect.  This no load voltage seems too high.  Can anyone point me in the right direction toward a repair.  I have read some post, but most speak of modifications.  I am interested in just getting it to work correctly.  One of the post I saw talked about adjusting VR-1 to the desired voltage, but in my case VR-1 has no effect.  Any help would be appreciated.

Jerry W5JDF Huh  
« Last Edit: May 10, 2012, 10:02:39 PM by W5JDF » Logged
W5JDF
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« Reply #1 on: May 10, 2012, 10:05:00 PM »

I am considering just replacing all four of the transistors in the PS and see what that will do.  I have located all the needed parts at Mouser.  Any thoughts?

Jerry W5JDF
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KA4POL
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« Reply #2 on: May 10, 2012, 10:14:29 PM »

Just before you posted the second message I was going to mention that the 2N5885s might be gone. This would explain the blown fuse. Also check the zener diode D3. As far as I remember it should have 9.25V.
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K8AXW
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« Reply #3 on: May 11, 2012, 08:54:33 AM »

Since you're going to have to make an order up for Mouser in any case, I suggest you get the 2N5885s,  the two transistors listed as Q1 and Q2 which are the regulator transistors and the zener diode as POL suggests.  Any of the three will cause your problem.

I've looked at two schematics online for the PS-30 and one  shows D3 as a Zener, one doesn't.  I have no idea what value D3 is but if you research this or look at the number printed on the side of your diode you can order the correct one.

It's quite easy to test the 2N5885s with an ohmmeter if you know how.  If you don't you can look at the data sheet (available at Mouser) and check the forward/reverse PN junctions with the meter.  It's really easier than you might think.  Otherwise, just replace all of the transistors and D3.

Just for grins, I'll bet that Q1, Q2 and or D3 are bad.  If you buy a set of 2N5885s and you present pair are OK, this will insure that you will never have to buy anymore in the future!   Grin
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KA4POL
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« Reply #4 on: May 11, 2012, 09:48:49 AM »

Actually the measured output voltage looks like the collector/s are shorted to the emitter/s. So it is possible that base to collactor/emitter seems ok. I had that happen also quite often.
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W5JDF
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« Reply #5 on: May 11, 2012, 11:48:42 AM »

It is going to be difficult to determine the value of D3 it is a small black and orange glass diode, most likely without any numbers, at least that I can see.  Still looking.  Jerry W5JDF
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W5JDF
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« Reply #6 on: May 11, 2012, 01:38:43 PM »

D3 is a xz-090 9.1v Zener Diode replacement number NTE139A.

Jerry W5JDF
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K4RVN
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« Reply #7 on: May 13, 2012, 02:10:27 PM »

If you replace the transistors , they may require some heat sink compound to set them in and you may need to order that at the same time from Mouser if you have none. My Astron needed it.

Frank
« Last Edit: May 13, 2012, 02:17:34 PM by K4RVN » Logged
W9GB
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« Reply #8 on: May 13, 2012, 05:06:19 PM »

The Kenwood linear power supplies (PS-30, KPS-10) and power supplies cards (TS-940S) of this era are Japanese designed and normally use 4 "2SC" style silicon transistors on an Automatic Voltage Regulation (AVR) board.
 These boards incorporate many features, BUT not over-voltage prevention !

A schematic diagram is mandatory AND you may find wiring errors on the schematics.
I found 2 of those 4 transistors on the KPS-10 AVR board were bad.  
The pass transistors tested, OK -- but I changed them out and mounted new ones with ThermoPads.


IF you replace the TO-3 pass transistors on the heat sink, use a new Mica washer OR
the new NTE Thermo Pads  (collector has +DC).
The Thermo Pads do not need traditional heat sink compound.
http://www.mcmelectronics.com/product/NTE-ELECTRONICS-TP0001-/TP0001
« Last Edit: May 14, 2012, 02:10:27 PM by W9GB » Logged
K4RVN
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« Reply #9 on: May 13, 2012, 06:21:02 PM »

I would also guess that the pass transistors are OK and the regulators are bad.

Frank
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KB1LKR
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« Reply #10 on: May 14, 2012, 06:55:32 PM »

NTE 139A = 1N4739A
zener, 9.1V, 1W, 5%, DO-41 glass case, only $0.14 ea for Fairchild at Mouser (cat #512-1N4739A )
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W5JDF
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« Reply #11 on: May 15, 2012, 10:15:55 PM »

Parts arrived today.  I ordered all four transistors Q1 & Q2 and on the AVR Q1 & Q2.  I also ordered the D3 diode.  Given the cost of parts and the cost of shipping it is a better deal to order everthing at once, since I have them I will go ahead and replace all four transistors and the diode.  Hopefully I will get it finshed tomorrow and be able to follow-up with positive results.  I do appreciate all the input and help.  Jerry W5JDF
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KA4POL
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« Reply #12 on: May 15, 2012, 10:26:19 PM »

In order to see which one is defective, please check out the removed parts.
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W5JDF
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Posts: 8




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« Reply #13 on: May 16, 2012, 07:24:04 AM »

Latest update:  He is what I know it is not.  It is not the diode (D3) or Q1 or Q2 on the AVR Unit, so next it is on the the two 2N5885's.  If that is not the probelm I am back to square one  Huh

Jerry W5JDF
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W5JDF
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« Reply #14 on: May 16, 2012, 08:47:02 AM »

Final Update:  One of the 2N5885 transistors was shorted.  I went ahead and replaced both.  Now I have a no load DC output of just under 16 VDC.  The PS-30 seems to be functioning within specification and has four new transistors and a new D3 diode so it should be good to go.  I do appreciate all of the input from everyone and the help guiding me in the right direction.  Even given the cost of the parts with shipping I still go the PS-30 really cheap.  Again thanks.

Jerry W5JDF
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