Bulk Capacitor Replacement Procedure for the PL 700B

Phase Linear Phanatic · May 27, 2013

Ok. This is my first real newbie question posted to all the PL gurus out there. I decided to upgrade the original 9,800uf caps in my 700B, with new ones from Nippon, rated at 18,000uf. What is the proper procedure for doing this and how are they supposed to be connected? I had no trouble replacing the light boards from Joe on several PL amps. However, I think I overextended my hand at THIS little task. Seems I did something wrong. :banghead:

For my left channel dropped out within the first 30 seconds of music playing. All fuses on the amp are great. Speaker fuses great. Line in RCA'S are tight. Diode block upgrade required perhaps?? Did I ruin them? I do not have test equipment for troubleshooting specific calibration of components etc. Just a basic multi meter. and the like. I'm worried I done blew something up big time? And on a side note: I always had the right channel meter being more sensitive than the left. Is there a calibration procedure to correct this? The veteran help here on this forum is very appreciated. I have attached a few thumbnails to give at least a partial picture of whats involved. The bottom amp is the one I'm working on. A Labratory Standard version. Let me know if more are required or any other info I can give you is needed. Otherwise........it's off to the old local vintage shop for repair! :confused3:

NavLinear · May 27, 2013

You need to eliminate the possibility of a mis-wire - that can get a little sporty. Did you take before photos - that will give you a reference. A schematic will help also. Did you get the caps from eBay or a reputable distributor such as Mouser? Counterfeit components are rampant - the distributors such as Mouser screen components and get them directly from the source so companies like this are the way to go.

Did you form the caps first? Read Joe's procedure for doing this:

http://forums.phxaudiotape.com/show...ower-Supply-Bulk-Capacitors?highlight=forming

Here is a document that Joe put together that contains installation procedures for a cap upgrade for a PL 400. These are very detailed so maybe this will help.

View attachment PL400 CAP Board Instructions.pdf

Good luck and post with your findings.

Dennis

NavLinear · May 27, 2013

Meter info:

http://forums.phxaudiotape.com/showthread.php/3508-Phase-Linear-400-Meter-Adjustment-Calibration

Gepetto · May 27, 2013

Phase Linear Phanatic said:

Dave did you check the 4 rail fuses in the lower right back of the amp to see that none of these are blown? Are these what you mean by the speaker fuses in your post? These are actually the B+ and B- fuses for each channel.

Did you check these caps before you installed them?

Here are some of the notes that I send to purchasers of our boards that want to DIY.

Capacitors that have been stored improperly or are very old may no longer be functional and may fail catastrophically.
It is possible to use new old stock (NOS) capacitors in this kit but make sure that they are properly formed before use and that the capacitor leakage current is proper at the rated voltage of the capacitor. It is highly recommended that you form and test NOS capacitors before deploying them in your application.

laatsch55 · May 28, 2013

OK, amp repair 101.

Do you have a Dim Bulb Tester? Do you have a variac? See attached pics. The only one that's a must have is the DBT. When hooked up in series with the AC mains in it will limit current by lighting the filament in the 100 watt bulb. In a normal power up the bulb will be bright for 2-4 secinds then start dimming as the caps charge. When the caps have charged and nothing else drawing current the filament will be barely visible. This little device will save you tons of heartache and money. If you want to get deeper into this fixin, get a variac. A ten amp model can be had on e-bay for 100-175, be patient and snag one. A variac limits voltage but not current, the DBT, a little voltage drop but BIG current drop. The ideal power up is the variac with the DBT plugged into it and the amp plugged in to the DBT.
You've demonstrated some ability by doing the LED boards. If you elect to take it somewhere be sure they are knowledeable about the PL's. They have some idiosynchrasies that can bite you in the ass. I also have a special built shipping container made just for the 400 and 700's should you decide to send it to me. However, let's take a shot at you fixin this thing now. With a meter you can tell a whole lot and in this case maybe enough.
First, check every nook and crannie for any solder splashes, component leads shorting something, wires touching, get down and dirty and root around thoroughly. You'd be amazed at how much trouble a solder splash can be. Check the fuses with your meter. When in doubt don't rely on a visual only. There are 2 fuses for each channel. One for the +100volts DC and one for the -100 volts DC. If one of these is out the amp will still play but lack a lot of volume and be very distorted. The fuse on the very bottom is the AC in. Check your fuseholders, sometimes they crack in the body and can drive ya nuts.
The bridge rectifier is not a stock unit but does appear to be wired correctly. If a BR is bad it can be a challenge to figure out and the best way to eliminate it as a problem is to check incoming AC and outgoing DC. That will tell us everything we need to know.
With the fuses and BR known to be good there are a lot of things that can be wrong with the symptoms you've described. Did this unit work ok before the cap swap?
Does this 700B have the PL020 driver board? From the pics it looks like it.
It may seem daunting and intimidating to begin with when something goes awry, but it's doable. Check those things I've described and post back. I have some of those same caps and from what I can tell they are in right if the red wire is gpoing to the positive post and the black to the negative you're good on those. It would be awfully handy to see the board up close and then take the board hold down nuts off and get us a pic of the back wall. A note of caution, support the board on the off wire end by a non-conductive any thing, don't let it hang in space as that will put undue strain on nthe board wires which are notorious for breaking whenever they damn well please. AND !!!!!!! put a strip of black electrical tape over the edge of the chassis that the board is laying over. If it's powered up and hanging out and being groovy there are some components that can short out against the chassis, and that young man can get messy. How do I know?? I think I can honestly say I have screwed up on fixin a PL about as many ways as you can. And it's never pretty and can cause additional weeks of work. It may seem like what we ask you to do is anal and tedious but really we're trying to prevent a preventable disaster. Don't be afraid to ask questions, there are no dumb questions when it comes to this stuff and alerts us to your level of knowledge about this fixin gig.

Before powering it up again unhook the +/- wires from the "bottom" of the caps so you can isolate the power supply while checking it. Be sure to insulate or isolate the unhooked wires so they can't short any thing.

We can do this...

Phase Linear Phanatic · May 28, 2013

I love this forum. Lee. (I assume it's Lee?) I will give you as much information as I possibly can. While addressing the other guys too. First, I checked and double checked the fuses on the back of the amp. ALL of them. Visually, they are fine, and with the DMM continuity test, they are fine. The fuses I have my mammoth 350lb speakers attatched to it, have 5A fast acting AGC's on the low end, and 3A fast acting on the high. (As I CURRENTLY have it bi-amped with a PL 400 on highs and PL 700B on lows) and THOSE fuses are perfect there. Process of elimination round one down. Now, sadly, I was unaware of Joe's cap forming technique, and took out the 9,800mf caps, and directly dropped in the Nippon 18,000mf ones. These caps I bought from ebay, from a guy with over 5,000 transactions and almost 100% positive feedback. In his listing for the caps, there is a model # that will take you directly to mouser. I have at this time since asked him if these are from them. (Just to cover my bases here). Now......I have installed four of Joe's light boards, and am on my way to six. The Light board used here is a WOA. It works great! So I figured I would be A-ok at this little project? oops........guess I got cocky. From the photo's provided in my last post, here is how I wired the caps. I followed a diagram in the back of the PL700B manual just to be sure. RED wires at top, go into positive side of top cap. Then negative side of that cap, hooked up to copper bridge rail. Copper bridge rail hooked up to lower cap on the positive side, and the negative side of that lower cap, hooked back up to BLACK wires at bottom of amp. I believe one red and one black wire are coming from the bridge rectifier as well. Unfortunately fella's, I do not have a Dim bulb tester or a variac. What I WILL do after this post is go back and triple check all my connections and make sure nothing is touching! I made sure to wrap each and every connection I dismantled from the original caps, with a paper towel, so as NOT to have myself touch or have the wires touch anything in the cabinet. (and look......I messed it up anyway). Yes the amp has been working perfect before the new caps. Note that when I installed the new caps, the bass didn't "sound" as punchy. Even when I tried to turn up the gains on the front panel under each VU meter. Then 20 seconds into the test, that left channel gave out. (as far as I went with the gains was 3/4). I have to say......I only have an Associates degree in electronics. And it's been over a decade since I used such knowledge. I don't feel like I should be messing any farther back into the amp, than the faceplate light boards themselves! :confused2:

The guy who sold me the caps said that if the the bridge rectifier is rated for 25 Amps, (which it is) the 18,000mf caps should work fine. And if the diodes were gone, I'd hear a huge hum. Since no hum and no bad fuses exist, I'm confounded. His last suggestion was to check the DC offset. I don't even know how to do that.

I have been contemplating just sending the amp to Joe and having him completely WOA it. Driver boards and everything. But if you think we can save the beast, I may consider sending it to you using your container. Just let me know what doing something like this is gonna cost me? :sad1:

My local vintage repair shop could probably do it. He worked on replacing an attenuation switch for this amp, when I found out I was missing the internal circuitry for it from the previous owner. And he worked on all my father's PL's in the 70's. So He's been there quite a while. But he's slammed and you can't walk 3 meters in that place without tripping over some piece of vintage gear. In all likelihood............I'm looking at a MONTH with no amp if it goes away for a tune-up.

Would dropping the old caps BACK in solve anything? I will recheck the connections and get back with you guys. So we can eliminate that. But it's open on the table behind me here, and I see nothing touching anything? I was super careful. Sighhhhhh........ I have to be off to work soon. I work evenings fella's. So I may respond later. Thanks for ensuring me I'm not nuts! Nice to know I'm not the only one who's screwed up a 700B before! :error:

LOL! (sorry Lee)

Phase Linear Phanatic · May 28, 2013

One piece of additional information I just got. The gentleman who sold me the caps is an ex-Dynaco/Hafler engineer, and he informed me these caps were pre-formed for me using 24volts for 8 hours of burn in time. So this should simply have been a plug and play correct? I also will note I swapped out RCA cables three times just to ensure I didn't have a bad set. And wiggled the RCA inputs on the amp to be sure of a tight connection. All is well. Hope that helps a bit more.

laatsch55 · May 28, 2013

Yes it is Lee, no need to be sorry, you are not the only one to screw up a PL amp. When I was first learning I used to buy junkers on e-bay for a 100.00 then smash my head against the wall till it was fixed. Changed a lot of components that didn't needs it.
It doesn't take long to swap the caps back out. BUT, pull all 4 fuses in the back, that will isolate the power supply from the rest of the amp, then check AC going into the BR and check DC coming out of the BR. That'll tell us a bunch. When we replace BR's around here we go with 50 amp in the 700's and 35 amp in the 400's. They're a 3.00 part, why not overkill.?? We don't know that you have screwed up yet, there's a lot of things that can happen as you do other stuff, an older part can get stressed, a wire breaks , etc.Is that a PL020 board??

laatsch55 · May 28, 2013

I see burn marks under the 3 tab terminals on the back wall, are those new?? Or as Joe calls it " A Thermal Event"

laatsch55 · May 28, 2013

Caps need to be formed at their working voltage. Read Joe's post on it in this section. I'm going to move this thread to the DIY section in a bit here.This forum is for PL alerts and stuff. No biggie.

Phase Linear Phanatic · May 28, 2013

DIY. Yes. More like "Do-It-Yourself-DOH!!" Apologies. Being new, I wasn't sure where to post this thread topic. I saw the most PL stuff here. So I took a stab! :confused3:

Yes it IS a PL20 board. I cannot tell you if that burn mark was before or after, as I nave never had this amp open this far back. Ten years ago, I DID have all the transistors replaced on this side cause of a dead short. It may be left over from that. But correct me if I'm wrong; isn't that the RIGHT channel set of transistors? And the other the left? I have the left channel that's out. I very well may just put the old caps back in and call it a day. I was trying to take something old and make it new. (to a point I guess) LOL! Take a look at the back of the PL20 board Lee. I noticed that third red wire from the right; on the left channel seems to be partially melted, exposing a sliver of wire. When installed, It touches the outer vertical transistor rail of the left channel. Would this cause no sound, no meter movement, yet no blown fuses?

laatsch55 · May 28, 2013

Yes it could. Anything shorting out the base or collector rails is a bad thing. If an output shorts it will blow fuses. If it just opens then , no it wouldn't blow a fuse. Let's not get ahead of our selves. Confirm that the power supply is working then we will go from there.

laatsch55 · May 28, 2013

the nsticker on the back wall says Val??? That's a new one to post in the Girls of Phase Linear thread.

laatsch55 · May 28, 2013

As you are looking at the front of the amp, the stuff on the left is the left or A channel, the right the B channel.

Phase Linear Phanatic · May 28, 2013

Thanks Lee! Yeah I've read that post before. Add VAL to the list! I guess that's who changed out the transistors ten years ago. I will work on verifying the correct voltages in the morning, and get back with you in the afternoon. I have to be off to work for the rest of the day. Thanks for the help guys!!

NavLinear · May 28, 2013

Dim Bulb Tester thread:

http://www.audiokarma.org/forums/showthread.php?t=465423

There are a number of ways to build this from exotic to simple and this design is simple - the parts cost for this won't break the bank.

Val would be the Phase Linear assembler of your amp.

Gepetto · May 28, 2013

Hi Dennis
I think I showed you the alternative to the DBT at one point, if you have the amp open, that is.

laatsch55 · May 28, 2013

OH???

Gepetto · May 28, 2013

DBT alternative

I think I sent these to you before too Lee. Pop the fuses and jumper like this.

laatsch55 · May 28, 2013

Yes Joe, ya did. That looks way handy, 100 ohm??

Bulk Capacitor Replacement Procedure for the PL 700B

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