Pyramid PS-36KX Power Supply Repair Highlights

[@wxman46]

I had a similar problem on my Pyramid PS36XX. It went into protection mode and folded one evening while I was using my ham radio. Initially, I found all four 3772 pass transistors had C/E shorts. I too bought some knockoffs from ebay stamped as "MOTOROLA made in Mexico". But in my case, after the repair, the unit seemed to be fine. That is, until I tried anything beyond a 15 amp load, then it would fold and go into protection mode. I cast the whole thing aside but did buy four new 2N3772s from a reputable source. A year later, I decided to give it another try. If it wasn't going to be a simple fix, it was headed for the junkpile. After removing the heatsink, I found all four pass transistors were fine. And then, the obvious hit me head on! The heavy red leads that feed the collectors of the 2N3772s in pairs are soldered to a heavy tab (as is shown in this video).. It happened that I had removed the wire during the initial repair for extra slack in the wiring and apparently didn't use enough heat when I reconnected them. One was fine but the other had broken away and was dangling. So,, one pair wasn't even contributing to the load! Sure enough, after the second repair, the power supply is now back to full output with NO annoying alarms. And I have four new 2N3772s still on hand, just in case the ones full of "Chinesium" break down.

[@AB1Vampire]

Thank you for posting. For the older PSU's, I replace the original regulator PCB with a preassembled voltage regulator to drive the pass transistors.

[@K5YVY]

3 years later I find myself trying to repair a pyramid PS21KX , I repaired a physically damaged transistor thinking that was obviously the problem, but it wasn’t. Still get only 1.7v with no load. I suppose after watching your video I’ll try your steps. Thanks Rob👍

[@SevenFortyOne]

Give it a shot and see what happens. If there is anything I can do to help, you know where to find me...good luck!

[@fathergratwick]

I just found the same k723 chip failure but everything else tests out fine so far so have one on order.. got this supply new in the box broken like this a few years ago and finally decided to repair since I found myself needing more amps for charging lifepo batteries

[@robertmeyer4744]

I have fixed a lot of pyramid supply's over the years . got a 52 amp in bench now. I use a transistor tester . some times you get leaky transistor and for best loading match the gain Hfe. you can use 2N3771 as long as input voltage not to high. the 3772 is same just higher voltage . the 2N3773 is higher voltage but less collector amps. I keep insulator kits on hand. Mouser has them. you can use tip 120 for driver even tip 3055 depending on supply . Them bridge rect go bad very often in pyramid brand, that what wrong with what I fixing now. doing a stud diode upgrade with heat sink . very tricky in small space. I did this many times before. also I have had problems with RF getting into the 723 and causing trouble .some inductors on sense leads and .1 bypass caps fix the problem .I have added fans to them. the 2n3771 on back has no air flow threw it. look as Astron for same amps. much bigger heatsinks stud diodes and a beefey transformer. I can say the 86 amp PS 86KX is great. what I own and use all the time . never had trouble . I have made my own 240V 200 amp with LM723 and 30 2N 3772 . 2N 3055 driver . fan cooled made in a forklift 48V 100amp charger cabinet .get a ball barring fan to replace the bad one. can mount a 80MM fan on back heat sink if user loads it up alot. also some times them 2.2 ohm resistor on base burn up. check them .watch for China junk parts . Mouser or Newark has the good ones. 73's

[@jp-um2fr]

Just found your channel, worth watching - subscribed. Just one point. There was a video on KZbin of a chap repairing a power supply and there was a lot of the usual 'Chinese crap' being said. Just one little problem, in small letters in one corner viewable to all were the words 'Made In The USA' . Personally I could not afford my electronics hobby if it were not for China. From the USA one LM317HVT was over £4 plus postage - from China £2.40 for 10 postage paid. I do under rate all power items and so far no problems - except yesterday. I had a 50 Amp bridge rect. go to a direct short across the AC. It had around 40Amps up it and boy was it spectacular. Tried another under load and no problems. Good old Chairman Mao. The video above was taken off.

[@SevenFortyOne]

Thanks for stopping in! I have a varied mix of topics in my channel. No doubt the Chinese components Help make this hobby reachable for more people

[@randyguay7115]

Great video. I just picked up one of these and i hope it works but for 5 bucks this was maybe worth fixing. And i am curious did you dig in and do the meters and fan.

[@SevenFortyOne]

No, the owner didn't want those changed

[@ianbutler1983]

Thanks. I had no idea there was such a thing as counterfeit transistors.

[@w9gb]

HUGE Problem. I only purchase components for DC power supply repairs from Mouser or Digi-Key. WHY would you use a UNKNOWN (Alibaba, eBay) Supplier for a Critical Component, powering thousands $$ of equipment??

[@SevenFortyOne]

Agreed.

[@AlexanderSafronov-v6k]

2 questions: 1. in this power supply protection of an exit against overestimate of 16 volts works at SCR. In my ps-36kx it is TYN825 (25A ! , 800V). it less than gives a source(32-35A) ! What do you think - is it will protect? 2. in my ps-36kx emitters of power transistors are connected directly to + C7, C9, and the shunt and the ampermeter stand more to the right - ONLY to OUTPUT exit. In this case protection on current has no current sensor. what do you think of work of current protection?

[@AB1Vampire]

Nice video, thaniks for posting. Your 723 Reg chip voltages wasn't that far off and 14 pins is a lot of soldering, twice! Was hoping you'd go more more into Series-pass transistors. They seem to go bad by shorting C-E.

[@dalekubichek5710]

If/when I would install a DIP socket, easy and makes life much easier and less burdensome to the PCB.

[@Kennynva]

I had a Pyramid PS-25G that stooped working...I came up with a LM723 bad...which is the voltage regulator...so I put a 14 pin socket that the IC can plug into, so I didn't have to re-solder the IC in if it went bad again. They fail pretty easy, especially if you accidentally run voltage backward up the negative line out..

[@SevenFortyOne]

I would have put in a socket if I had one handy. I think you are right though, the 723 was probably the root of the problem with this unit.

[@Kennynva]

I didnt know that..so what IC is going to replace the 723?

[@dr8418]

Helped give me some ideas on mine which is doing the same thing. The difference is that mine is only a year old and the one in the video is an old train wreck. Hardly worth trying to fix. The unit is only $150 new.

[@greenharvestproductions6743]

Have a similar problem with a power supply made by the same company. Pyramid 52 amp seems like the fan. When I turn it on starts to run then it slows down and completely it goes off did you ever find out why the fan was not working? I'm having the same issue with the fan. Is the fan supposed to turn off for a few minutes and then slow down or is the fan supposed to stay on constantly or does it turn on only when it gets warm it needs to be cooled down. I really appreciate if you can help me. Thank you very much kg4acg Sgt Velez USMC ret

[@kennynvake4hve584]

I would advise to put a socket for the 723 seems mine fails more than it should on my 25 amp pyramid supply. If the power out leads are shorted, even the slightest amount the 723 will fail.

[@SevenFortyOne]

Good tip!

[@taadventures6312]

I have the same one but is brand new. Out of box. And is doing the same thing. I turned it on and it worked. I then hooked up my Stryker 955. And was still working. The bolt meter wasn’t working so I tapped with my finger where the meter is and that’s when it started beeping and the protection light lite up. I never keyed up my radio. Any ideas. Thank you. Great video

[@SevenFortyOne]

Hard to say without being able to test it. Check all your connections and make sure they are good. If they are then it might be time to fix this unit up.

[@scramick]

I accidentally fed 24VAC to the output of the Pyramid PS26KX and blew something. Now I only get the "PROTECTION"" alarm and no output. I replaced the LM723 IC, but this did not do anything. Do you have any suggestions to get this working again? Any help is appreciated. Thank you!

[@jma8352]

thanks for the great video! i have a ps35 i got on ebay. blowing fuses so im wondering if i should check the lm723 first because the transistors look new. also is thare an easy way to tell if the tranformer is shorted to ground? thanks again!

[@SevenFortyOne]

I don't remember the circuit in this but use an ohm meter to check for shorts from the primary and secondary leafscto chassis. Transformers often fail open, not short so the problem may like elsewhere. Even if the transistors look good they may be bad.

[@w9gb]

CHECK your NPN pass transistors FIRST (2N3771 or 2N3055). DISCHARGE Electrolytic BEFORE Removing or Installing the uA723/LM723 ... watched new student destroy one (when he didn’t). I have also found Cracks in the Mica insulator. TO-3 transistor case is HOT (16-23 VDC) ... a Short will blow fuse.

[@Dennis-mq6or]

Replace the 1N5393 zener diode that protects the voltage regulator IC while you are in there. Voltmeter is a simple series circuit, the meter and two series resistors, a 30K and a trimpot to adjust the reading. (make sure you are adjusting the correct trimpot). Ammeter is similar series adjust, but monitors the voltage across a current sensing resistor.

[@jamescampos9358]

Hello,I have a power supply from MFJ-Model 4035MV. It was stored in a box for over 10 years and worked back then. Now I just set it up and the VOLT METER FLUCTUATES from about 5 volts to 12. After it is plugged in to the AC outlet for about 5 minutes it stops at 13.8 Volts.But if I try to adjust the voltage the meter starts to fluctuate once again but does not go pass the 13.8 volts reading.What do you think is the problem with this power supply? I do NOT want to fry my radios.

[@SevenFortyOne]

The voltage control may be dirty, or you may have bad capacitors...could be anything really. It's hard to tell without being in front of it myself

[@jamescampos9358]

@@SevenFortyOne Thank you for the information.

[@Mr_Meowingtons]

EVERY Pyramid PSU I have ever opened up had 25 Volt caps riding right on the edge of there voltage rating they really need 35Volt caps. the moment you told us he got E-Bay Transistors I was like there Fakes! if he got the caps there too going to guess there fakes too.

[@fathergratwick]

Depends on who you purchase them from on ebay, obviously if it ships from china and its not a chinese made brand, its suspect.

[@Homer19521]

Where did you get the blue top layer for your bench? Thanx - Bob

[@SevenFortyOne]

It is a used anti-static mat that was discarded by my previous employer. You can buy this stuff new from places like Grainger or maybe even Amazon.

[@jasonblessing3644]

Hey their I'm only getting 11.8 volts on the terminals and moving the voltage adjustment not changing could get back with me with any idea it's a ps-52kx pyramid and have new capacitors I installed and still doing be nice can get back with me

[@davidabbott8719]

Do you actually work on can radios?

[@SevenFortyOne]

I work on my own radios only if that's what you are asking

[@cx4557]

I have one of these with the 2n3772 transistor, but the schematics I find online specify 2n3771 transistors. Any issue using the 2n3771s (local shop has them in stock, but not the 2n3772)?

[@SevenFortyOne]

Check the data sheets on both parts...I think they will work for this power supply. I think the 72 parts are higher voltage but otherwise the same but I'm not 100 percent sure

[@cx4557]

@@SevenFortyOne The 771 has lower voltage but higher amp rating. Will try it out. I tested the transistors today following your walk through and was able to confirm they're bad. Thanks!

[@py1am]

Good evening, I'm in need of a power supply regulator board Pyramid model PS-36k. Does anyone know where I can get it? Grateful

[@Haxsaw67]

can you share where you got the voltage matrix from for the IC 723 chip? did you test the voltage on the chip once you replaced it?

[@SevenFortyOne]

I don't remember...maybe the mfg datasheet. Or the schematic I found. Sorry I can't be of more help

[@Haxsaw67]

@@SevenFortyOne i found it, thanks

[@CougarsUnlimited]

The 723 chip voltage matrix is found in many of the Astron power supply schematics such as the RS-35M.

[@ericegert7566]

mine was working - now pegs out on Amperage and blows the fuse without any load. What could it be? I also am having a hard time finding the real fuses - what came out was a 8A 32V but manual says 6A? 7.5A from Autostore continued to blow. Any help would be appreciated! :)

[@lgcacher9205]

First things you need to check the bridge diodes so see if they are shorted. More than likely that's your problem. If the diodes are good. Then check the scr device it could be bad

[@hazard025]

the regulator board in my nippon america dosent work...can i bypass i by building another 1???

[@SevenFortyOne]

You know your abilities better than I do so whether or not you can do it I can't answer but it sounds like it would be possible

[@joestevens9152]

My 36kx just went into protection mode, evidently when it was on, the positive wire hit ground. so therefore the protection circuit is now screaming. HELP!!!... just wondering if you have any ideas before i tear this down.

[@SevenFortyOne]

The owner of this supply reported doing the same thing (shorting power and ground) just before it quit. Try letting it sit for a while to see if it "resets". If that doesn't work you may have to replace the pass transistors and regulator chip like I did. I Also suggest checking the filter caps while you are in there and replace them if needed.

[@nelsoningalsbe8262]

what is the Secondary Voltages im trying to find a new transformer 73's n4jrs

[@SevenFortyOne]

I don't remember...and this was my buddy's power supply so I gave it back to him which means I can't take any measurements.

[@KEVINPAGEkf4znl]

I have one like this and the amp meter is not working where would I start look for the problem?

[@rusty1187]

start with checking continuity through the meter with a loading resistor in series

[@AlexanderSafronov-v6k]

the scheme which you show is signed as ps-26kx and the movie about repair of ps-36kx. Whether you can lay out the link schematik diagram on 36, or at least describe a difference.

[@SevenFortyOne]

I am not positive but I think the main difference is the size of the transformer - the ps-36KX transformer is bigger.

[@AlexanderSafronov-v6k]

thanks

[@tvtech2582]

Maybe the Christmas lights are the wrong value,Ha Ha. Hey I just watched another You tube channel the other day where the suspected Chinese Motorola transistors,same TO2 case were the fault,so they took a dremel tool and cut the tops off to compare and sure enough they were completely different inside. Seems like this is a common problem with Ebay, Steve.

[@SevenFortyOne]

The Christmas lights were a little odd, but I'm told they worked well. That video you saw with the transistors and Dremmel tool was probably mine..I uploaded it a few days ago. The Chinese transistors in that video were the ones that the owner of this supply gave me for the first go-round....junk.

[@headpainter1]

My brain has a difficult time with electric. Somebody point me in the right direction please. Ps-36kx had no power out after I oops it.... I replaced the transistors because they tested bad, now it has 12 to 12.1 volts out but not adjustable via knob. Is this a 723 chip problem you think? This all started (oops) because it was working but i hooked up a million cp 12v spotlight which worked about 3 seconds then ps went into beep mode. The adjustment knob has never worked since i got it second hand. I would like to get adjustment knob working if somebody thinks its the 723 chip, ill replace it. Currently working but holds 12 to 12.1 volts out (not adjustable). Thanks.

[@judges69]

35 or 50 v caps may of been better if you had to buy them

[@SevenFortyOne]

I agree..the owner, however, supplied the parts so that's what I used.

[@buzzsah]

Cheap parts are a pain in the ass, when you think you replaced the old parts only to find the new was bad.

[@SevenFortyOne]

Cheap parts just aren't worth it...you get what you pay for...

[@miguelsalami]

LOOOOOOONG➡ViiiiiiiiiiiiiDEO❗

[@Driftdavillian]

But very detailed & helpful

[@GoDodgers1]

I am not happy with pyramid supplies. I have bought several and none of them lasted over 2 years. I believe RF just flows through the supply and the supply isn't built to deal with RF. So why would you buy one of these for if you aren't using it for the radio room? Junk from the factory. Buy Astron (even this doesn't like RF). Or even a switcher like TekPower (dead silent, no hash). Personally, this repair probably wont last long either so it's not worth the time or expense.

[@Chris-hy6jy]

I wouldn't buy any electronic components off eBay or Amazon.

[@lesstime1678]

continua a ir para casa do tio painha para aprenders a asobiar as casbras porque ainda tens muito para aprender ,so depois de ires lidar com ele por uns anos aprendendo como se asobia as cabras podes vir para ca e falar a respeito de electroni's ,por agora ainda estas muito verdinho para tal coisa

[@theshitshow6371]

Have a Pyramid model PS-32LAB and the Ammeter wont work, just the voltmeter works. Its impossible to find a schematic so I don't where to begin troubleshooting. Any suggestions?

[@SevenFortyOne]

I'd guess that if everything else is working the ammeter is probably physically stuck or broken. Having said that, if there is a part number on your circuit board try searching in that.

[@theshitshow6371]

@@SevenFortyOne unfortunately theres no part number on the PCB. But I tested the Diodes and the Pass transistors and they all checked out fine. Its a 30V 5A power supply. I tested the voltage and current, its putting out approximately what its suppose to. The ammeter cpil winding looked a little unraveled with creases in it when I looked inside of it.