Hey- just got this head about a month ago and has sounded great up until yesterday and today- a few times the volume dropped and made a fuzzy/farty sound but came back to normal within a few seconds. Sometimes it did this but did not return to normal and I switched it off and back on and it was fine. Sometimes it sounds a little crackly or static-y too often just before it drops in volume. :'(
Checked all connections to the amp and effects, guitar, etc and I'm pretty sure it is the amp.
Any ideas what to check first? I'm no certified amp tech but I can open it up and clean, solder and probably replace something if necessary.
Thanks.
First thing first... Does the amp respond to the Enzo test??? What is the Enzo test? Well we just call it that in forums here and there, it is about whacking your fist on the amp. Yup, ball you fist up tight and when the amp fails give it a nice whack - any change to the amp? Or does whacking the amp cause changes to make it fail, you get the idea? We are looking to see if something in the amp is loose or intermittently connected. Solder joints are the first suspects, but try this test first.
Sometimes the Enzo Whack test does not give us a response, but there still could be something loose in the amp. Opening the amp and using a chopstick is a great way to test for intermittent connections. With the amp running you wiggle components around using the stick. Main thing here is to use a non-conductive stick for touching anything inside the chassis. Try some of this and let us know what you get... Good luck
Here is the prototype for the Enzo Whacker!! 8)
(http://l-userpic.livejournal.com/60869961/12363272)
:dbtu:
Hey DrGonz! Thanks for the ideas...
Ok-
1. Performed said Enzo test while amp was on and no pops or crackles when tested.
2. Poked and prodded all accessible joins and connections with kabob skewer. Again, nothing.
3. Remembered that the issue only seemed to occur at higher volumes (above bedroom levels- which is anything above 1.5 lol). Ran it for about 20 minutes at higher volume connected to iPod loaded with favorite tunes.
4. Went back and poked and prodded again. Still nothing.
5. Noticed excessive amounts of contact cleaner solution on wires from when I hosed the pots about a week ago. Used Q-tips to swab off best I could. This would correspond with the cutting out sound (never happened before this). However, it also never happened while volumes were relatively low which is the way I mostly played it until recently (when the cutting out appeared).
6. Just went back a poked and prodded some more... nothing.
7. Observed dog does NOT like "What I Like About You" by the Romantics. He ran around trying to find a place to hide from the sound. Skipped ahead to "Roadhouse Blues" and he is fine now.
8. Cranked volume up to 8 which I could only handle for a few minutes and still nothing abnormal sounding. Poked and prodded too. Whacked it too.
9. Took some pics while I had it open.
10. Disconnected iPod and plugged in guitar and played fairly aggressively at higher than bedroom levels and nothing unusual.
11. Noticed a low-level hum (not buzz) that I had heard before but not always. Switched off the amp, turned it back on and the hum was gone.
Nothing looks loose. The low-level hum is now a concern. At least one of the big grey transistors (?) looks like there is some reddish-brown corrosion around the edges of one end. Doesn't look like anything has been replaced ever on the board but I wouldn't know for sure.
So that's where I am now.
Ok- Had just tried Enzo test again and there is clearly a static-y sound.
No iPod or guitar plugged in- speakers in but no input. Volume up and if I give the casing a whack, I can hear it. Probably didn't hear it before because I was playing my iPod through it at the time.
If I tap the PCB board it happens. Really, if I tap it anywhere, I hear a crackling sound coming through the speakers. Not really loud but it is there.
After more poking, seems like this static is associated with the reverb.
The leads are disconnected and one makes a static noise when jostled. But also when the board is or case is tapped without necessarily moving the lead.
No noise when reverb dial is all the way off.
So like I said the Enzo test does not always give a response. We could assume that it could be heat related if the failure takes time to occur, and you might have been jamming for a while before you had any symptoms. Now assuming makes a you know what out of me and we would need to have to trace signal/voltages to really prove this theory. Plus we need to keep the unit running for periods of time to heat it up to make it fail. It can be cold solder joints or the actual component that's failing. Finding these types of faults takes a bit of time and patience.
Now look at the preamp out jack in the back of the amp near the power plug. I am pretty sure that is a preamp out jack with the yellow and brown wires running to its lugs. When you plug in a cable to that jack does it cut out the speaker output? Try that and lets us know. Just need to know if the grounding of that jack is dirty causing it to shunt the output. From the sound of your explorations into amps I can imagine you cleaned the heck out of this one already. Still that jack might have an ability to cut out the preamp feed to the output of the amp. Just need to check to know for sure since I am not looking at a schematic.
Let us know if you experience any symptoms now that you are looking for these to occur. Also, what type of load (speaker) are you hooking up to this amp? 4/8/16ohms? What does the output say to hook up to the amp?
Also, that static noise might be nothing or it might be cold solder joints responding to the tapping of the pcb board. It's hard to tell really.
Hey DrGonz-
That's actually the footswitch jack but I plugged into the preamp out (next to speaker out) with 8 ohm load cab plugged into the speaker out jack and the speakers did not cut out.
Owner's manual says they can take an 8 ohm load for 75 watts or 4 ohm (min) load for 121 watts.
Thanks.
Quote from: ChewyNasalPrizeseems like this static is associated with the reverb.
The leads are disconnected
No noise when reverb dial is all the way off.
Ahhh-Ha! Well if the reverb tank output is disconnected that might account for some hum injection, and "cable rustle" suggests that the reverb return is pretty sensitive. If this is the case then it might respond to the reverb footswitch.
Also, give the Preamp Out another small shot of contact cleaner and work a plug in and out a few times. This socket will have bridging contacts for when it is not in use, and these can get tarnished and go intermittent.
Ok-
I cleaned all the jacks again, worked plug in and out, hooked the reverb back up and jammed on it at higher volumes and it still cut out. A slight crackling sound precedes a drop in volume with a tone that sounds farty and flubby (not unlike a blown speaker to my ears). It only lasted a second or so the few times it happened this morning.
No footswitch is attached. Happens if reverb is on or off.
Appears to only happen at louder volumes and on heavy attacks. Playing lightly or at lower volumes doesn't seem to make it happen.
Cab is detached. Head is on a table cab is on the floor so excessive vibration doesn't seem to be contributing.
Take the Commanders preamp out and plug it into another amp or something. Remove the main speaker connection. Test the amp in this manner to see if the preamp is responsible for the drop in volume and other symptoms.
I did as you suggested and it did NOT fart out! Played it loud and long and it sounded GREAT running through the power section of my Peavey Classic VT 212 (two 6L6s in the power section). It sounds BETTER to me running through the Peavey (stronger). I was just using the Peavey as a cab for the Commander so speakers haven't changed. But wow. No crackling or even a hint of misbehaving. Sounds really punchy and clear/clean and heavy attack single notes or chords really power through. The two together sound better than either does separately. Anyway... I digress.
So, yeah. Doesn't seem to be any problems with the preamp on the Commander. :dbtu:
So this helps us negate between which part of the amp is the culprit. So it's looking like the power amp is where we have the trouble. The problem could be power related and it could be a simple fix like soldering some components better. It could be many other things too, so lets just start with the most basic items first. Analyzing signal and power voltages to see what occurs when the amp fails is crucial to really troubleshoot here.
So how long do you have the amp on before it starts to crackle and volume drops out? Do you have a Digital multimeter? If you do not feel comfortable checking voltages that is okay. When I first was learning how to read voltage from amps there was a lot of information and terms I had to absorb. I am wondering if there is a schematic that we can find for this amp. I had looked but is this the Commander II or the very original Commander? Probably pretty close schematics, so lets look for something that has this amps power amp stage drawing.
Yeah I just fixed up an old Peavey Classic amp(1976) with the two 6L6 output stage. I am waiting on some transistors to get the non-working tremolo circuit working again. I like the idea of having a warm tube output and a solid state preamp. Sounds like you stumbled upon a nice combination of tone with the Commander and Peavey amps. :dbtu:
Edit: Here is a link where Juan revealed what the cat brought home... LOL It is a schematic for the the RG120 Commander II and hopefully the power amp section is very similar to your amp. We will have to see if that is the case though. This is the preamp info mostly and only shows the part about the power supply.
http://www.ssguitar.com/index.php?topic=2117.0
Yeah, the Randall/Peavey combination sounds fantastic! Might try running a couple of other amps through the Peavey and see how they sound. It is my only amp with tube power section that has power amp in option. Would never have tried it if I wasn't having problems with the Randall. From lemons come lemonade! :)
My Peavey is a '79 with phaser. Randall is a '79 also.
Ok, back to business...
I think the Commander and Commander II are pretty much the same. I believe the numbers following the name indicate the number of speakers in the combo (I, II, IV or no number at all for the head). Not sure if there are any real meaningful differences in circuitry among them.
If I start with volume cranked up loud enough to where it cuts out (never cuts out a bedroom-ish levels), it only takes maybe 10 minutes or so before it poops out. It isn't highly predictable though but that has been mostly the pattern so far. Sometimes it cuts and stays cut. Sometimes it cuts for a second the comes back. But always seems to be preceded by a crackling/static sound just before it goes.
I do not have a digital multimeter. I do have one with a needle though it is pretty cheap. I got it to check the resistances of unmarked speakers. I'll get a digital one though. Be a few days before it arrives. Any recommendations on brand/model? Probably need one with little clamps on the end of the wires?
LOL- I saw that thread with the schematics! What a coincidence. I love this site. :)
Have you tried plugging a known good lead into Fx Send and Fx Return and tested it like that?
Nuthin' wrong with an analogue meter (beats sticking your tongue on it).
I'll just remark again that this has a rather unusual output stage where the drivers provide the low level output and the output transistors don't start operating until the level gets up a bit.
Quote from: ChewyNasalPrizeProbably need one with little clamps on the end of the wires?
The ones with the little claws at the end sure are handy, e.g;
https://www.elfa.se/elfa3~se_en/elfa/init.do?item=40-443-01&toc=18768 (https://www.elfa.se/elfa3~se_en/elfa/init.do?item=40-443-01&toc=18768)
Those power transistor sockets are generally quite good, but still not above suspicion.
Thanks Roly!
This one doesn't have effects send and return. Just the high/low inputs for each channel and the footswitch, speaker out (only one jack) and preamp out.
Just to make doubly extra-sure, I played it a good while at bedroom levels to see if it would fart out using it's on-board power amp. Nothing. Then I turned it up a little over "1" and after playing for about 10 more minutes it started to crap out intermittently (sounded fuzzy/buzzy/muddy with a drop in volume but not much). It came in and out for several minutes then after about 5 minutes, it stayed farted-out. I switched it off then back on and it was OK for about 20 seconds then it did it again. Switch it off and back on and it stayed farty.
Also, there was a low-level hum that was present at the same intensity no matter where the volume settings were placed. This happened before but I thought it was because of the disconnected reverb (which is now connected) but the hum was back along with the farty sound. Swiched off the amp and back on quickly and the hum was still there. Switched it off and left it off for a several seconds then turned it back on and the hum was gone.
Still we have a hum and a crackling fart to worry about lol. I am attaching that same schematic from previous post but this one shows the power amp side of the page better. There are plenty of test points to analyze. One idea is to test the output of the amp with your multimeter set on DC Volts. Clip a lead on both end of the output speaker jack, black on jack sleeve and red on the jack tip. Easy to clip on the solder lugs if you have the amp out on a bench. Have the speaker plugged in and when it starts farting, lets see if there is any DC at all on the output. I don't think there will be but if there is then we will need to stop connecting a speaker to the amp. At least analyze the speaker output to make sure what we are putting out of the amp onto the speaker. More ideas will come as we all proceed from this point further and there are some great troubleshooters here at SSguitar.
Note: Mainly just wanted to update a post here with this other copy of the schematic.
Thanks DrGonz!
Waiting on a new multimeter. Will perform suggested test as soon as it arrives!
:)
I got a set of clamp adapters for the analog multimeter I already had. Want to see if this works first before I get a digital one.
It has three ranges for DCV: 10, 250 and 500. Which range should I use?
I also got a can of that spray-cold stuff to check transistors if it comes to that. I've never used it but it might come in handy.
Now I just have to wait for the little woman to leave the house so I can CRANK it! :)
Well the main thing we are wanting to know is when that hum begins if it is a sign of DC voltage onto the speaker. For one we don't know what is at fault and for another we are not sure if the fault occurs without a speaker load on the amp. Right now we know with a load it fails at higher volumes. I don't expect to see DC on the output but then again better safe than sorry.
So connect black probe to sleeve and red probe to tip on the inside jack. Run signal through the amp and wait for it to fail. At that point check the reading on the voltmeter, then turn off audio signal. Keep the amp running with speaker connected and check the reading on the voltmeter. Disconnect the speaker from the amp and check reading on the meter. Every time you check the meter do it on the 10 setting then the 250 setting and take a quick note. That way we will check if there is voltage above 10vdc and better accuracy if there is any readings below 10 vdc. Better accuracy would be a digital meter, but really we are looking to see if there is more than 1/2volt on the output once the failure begins. Let us know what you find out.
Note: I am not sure the accuracy of the meter you have now if it is not digital, probably okay. We might be seeing only millivolts of DC on the output and not so sure how well that meter will display such small readings. A lot of times the output will have a range of 0-500mv DC on the output of many solid state amps. Sure we ideally want to have no DC voltage on the output, but that is rarely the case.
OK- I think I found something... :dbtu:
I connected the multimeter as described then plugged in and turned on and the needle didn't move at all.
I played at volume set at 2 (highest so far lol) and it cut out right away. I hadn't played the amp for several days. Noticed the meter needle still did not move on either 10 or 250 settings.
This time it stayed cut out so I had a constant farty signal. While trilling on the guitar with my left hand to maintain the signal, I poked around again with the wooden kabbob skewer with my right hand. When I pressed on (what I believe is) the negative connection of one of the filter caps, it stopped cutting out right away. It went to a clean signal and I could not get it to fart out again after playing for several more minutes and while pressing and prodding the connections of this filter cap.
Solders look OK to me but maybe something needs cleaning or resoldering or possibly replacing?
Picture of the location marked by kabbob skewer of what I think is a bad connection and at this point the most likely cause of farting is attached. :)
Also- I think the "hum" was associated with my guitar being too close to the amp while I was testing it. I was wearing it while testing so it was only inches from the transformer at times.
At least I hope that's all it was.
Just played it some more and for a good while at high volumes and it NEVER cut out. It also sounded "punchier" it seemed. Maybe my imagination.
Quote from: ChewyNasalPrizeWhen I pressed on (what I believe is) the negative connection of one of the filter caps, it stopped cutting out right away.
Yep, that is normally a pretty strong clue you are hot on the trail.
Quote from: ChewyNasalPrizeI think the "hum" was associated with my guitar being too close to the amp
That will do it.
When testing you are generally better of using an MP3 player, cassette deck, or radio as a signal source because you don't have to try and do two things at once, and you aren't clinging on to grounded guitar strings with one hand while poking around in the innards with the other {yes the "chopstick" is insulated, but it's still not a great idea}.
Try giving the cap lug a bit of a wiggle and see if you can determine if it's the solder joint, or perhaps the lug is losing connection inside the cap. Try re-soldering the whole joint, but if that doesn't clear it up then it looks like the cap might have a faulty internal connection. You certainly seem to have "touched" the fault, which is progress.
Quote from: ChewyNasalPrizeMaybe my imagination.
Sorry, but yeah, that is a fairly well-known subjective effect.
Well looks like we are now back to the earlier tests proving that something is loose/intermittent. Much better than something starting to fail and putting DC or something on the speaker. Still I am confused by one thing this whole time... The preamp test showed that we could not get the amp signal to fail running it into the Peavey hybrid amp. So apparently this little intermittent connection is very elusive.
Does your meter have a an ohms setting? With amp off, touch black probe to that negative terminal and red to the other end where that black wire goes. We are looking for very low resistance here 1 ohm or less on the meter. Does the meter have a continuity setting? A continuity setting on a meter will give you a beeping noise to let you know there is low resistance. It is good to have a that beeping sound going on and then you might wiggle the wire to check it for shorts. The ohms meter will do the same thing but is harder read on an analog meter.
So it could be bad solder joint, bad black wire, and the filter cap might have an internal shorting developing. I guess it could be more than those 3 ideas there but lets start here.
You can also place your probe over the connections of that cap and check the DC readings. Black probe connect to the chassis ground and red probe connects to each side of the filter cap. Meaning we will be measuring each leg of the cap one at a time. Try the black one and you should see negative DC voltage, set you meter to read 250.
When grounding your meter connect it to the green wire to clip it to where it bolts down to the inside of the chassis. The black spray might prevent a good conductive ground surface. Also, there are two black wires that connect to the pcb board and perhaps thats why preamp is not failing earlier. Perhaps not... Either way make sure to wiggle those wires around, especially the thick black one.
Yeah and Roly is dead on there about using a signal other than you playing your guitar at the same time as prodding with the stick. Good luck
OK- There are three terminating points from that joint. Two to the PCB board and one to the other filter cap. Readings at all points read below 0 ohms.
My meter does not have a continuity setting.
I checked the filter cap connections and while the amp was off, the needle did go slightly into negative territory when I touched the connection for the red wire. It didn't seem to do anything when touched to the black.
I also checked the other filter cap and same for the black but it went slightly into positive territory when I touched to the connection for the red wire. I guess this is normal?
I wiggled the lug but didn't cut out.
I'll resolder that connection and report back.
Thanks guys!
Quote from: ChewyNasalPrize on December 02, 2013, 07:18:02 PMI checked the filter cap connections and while the amp was off, the needle did go slightly into negative territory when I touched the connection for the red wire. It didn't seem to do anything when touched to the black.
I also checked the other filter cap and same for the black but it went slightly into positive territory when I touched to the connection for the red wire. I guess this is normal?
Yes very normal indeed. You now see the residual voltage of the cap is positive on one of the red terminal lugs and negative on it's corresponding filter cap. Those are your amps B+ rails that provide the higher voltage to your output section of the amp. They will also use that B+ voltage to drop it down to a lower voltage for the preamp section. Now you see how one cap is the positive side and the other negative side of this equation.
Ok-
I clipped the three wires at the solder joint, removed existing solder and cleaned the tip of the connector. Stripped the wires and reconnected to tip of the filter cap connector and resoldered. It's about as clean a connection as I know how to make.
Played it for a while at high volumes and no trace of cutting out. I'll leave it open and test from cold to hot several times over the next few days. It may still yet be the lug connection inside the filter cap and my fooling with it made it have a good temporary connection so I'm not totally ready to say it's fixed but I am pretty sure at least the problem lies here with this filter cap and/or connections to it.
It doesn't look like the lug comes out of the filter cap- should it?. If it is the lug, I'm guessing new filter cap? Or maybe both filter caps for good measure?
Thanks guys!
My intuition is that it's internal to the cap, possibly one of those rare manufacturing defects that slip by from time to time, but as with all intermittent faults only exhaustive testing will tell.
If it never shows up again it was (most likely) the solder joint. If it farts just once more it wasn't; and yes, I'd certainly replace both caps while you are in there.
No, if the lug comes out of the filter cap it's busted. :o
Just jammed on it some more and still good.
Gonna give it several more days of periodic blasting just to make sure before I put it back together.
Be nice if it wasn't the filter cap but wouldn't hurt to replace them if it is. If they are original they are 35 years old!
Either way, I'm glad we seem to have zeroed in on the problem. :)
Thanks!
Nice Job! Hopefully the sucker stays a rocking!! :dbtu:
Yup Roly is totally on point about replacing the caps if it farts out on you once more. Those are definitely the original filter caps or at least I would bet money on it. Replacing the filter caps is like having a piece of mind feeling about the amp. Though it is always pleasant when filter caps remain healthy for a long time.
Well, I jammed hard on it a few more times today and clean as a whistle.
Put it back together and jammed some more and still good.
Tested a total of about half/dozen times after solder job and no problems. Before it would have farted out every time, especially at the higher volumes I knew to be sure and test it at.
Also ran the preamp through the power amp of my Lab Series L5 and it really sounds good there too. Again I think better than the head to cab alone.
Anyway, I'm keeping my fingers crossed and will feel really good after a few weeks or so without incident.
This sure has been fun and educational for me. Thank you DrGonz and Roly for your help on this. I could not have done it without you! Bless you and bless this forum!
Now I gotta find something else that needs fixing.... :lmao:
Chewy
:dbtu:
While that's good and pleasing and all, a note of caution is in order - we don't really know for certain that it was a dubious solder joint, it could still be an internal break in the cap that has been jammed back together by the work on the lug, and as Murphy's Law dictates, this will only reappear when everything is bolted down good and you are in the middle of a career make-or-break audition.
I want to stress that if it does it again, at all, then take both caps out and shoot them - no messing about, okay?
On the other hand if it's still solid after a few months of rocking out you can start to relax, it was the solder joint. :tu:
I heard that man!
At least for now, the Randall isn't my main gigging amp but that may change after it proves itself repaired because it really sounds great and especially sounds good with the pedals I have- at least compared to some of my other amps. And it's got that KILLER on-board tremolo!
My thinking right now is to have the Randall on hand as backup for the L5 or Peavey. If either of those go down, I can run the Randall through their speakers. That way I don't have two 212 combos to lug around but still have a good backup plan with plenty of juice and things stay fairly simple.
Of course I need to be sure it is going to work if I NEED a backup so a few more weeks of no probs and I'll be comfortable. :)
Also, does replacing old filter caps that aren't necessarily "bad" have any potential positive effect on the tone of the amp? Sort of like a tone tune-up? Will it make the tone brighter/stronger/punchier/more resonant, etc... Or is it one of those things where it is either pretty much working or it's not?
I can't help but think after running through the power amps of the L5 and Peavey (which I had a local shop overhaul [before I found this forum]- has new filter caps and a few other bits) that it might benefit tonally from some new replacement parts? It might be worth it because it looks like a pretty straight-forward job that I could do myself (with your-all's guidance of course).
I don't know... Maybe I just I need a fixing fix. :lmao:
Thanks!
Changing the main filter caps will not change the tone. The subject comes up time and time again and it is worth researching replacing filter caps old vintage tube amps. They will claim that the sag in the power causes the amp to sound a certain way, or something or another... But with solid state amps I have yet to read of such stories. For me changing the filter caps is like replacing your old car battery. There are capacitors that are for the signal in the amp too and changing cap values in tone circuits alters the sound. There is even a debate about different brands and types of caps whether one is superior in tone. That debate is even harder to follow as it is very subjective and most of the time people can't agree, so they argue. Filter caps are there to smooth out the DC voltage and to remove AC ripple from the mains power. If the amp starts humming that can be a sign of a filter cap problem. Either bad solder joints at the terminals of filter caps or they are not filtering the AC, and you get hum. Personally, I would just change those caps if I was planning on keeping the amp for a while. Just take your time picking out the right parts before you order and ask questions to confirm.
Agree with the Doc.
When electrolytic caps fail they generally do so by losing capacitance, and in the power supply this will result in increased hum levels. With supply decoupling caps down the signal chain it may result in instability, unwanted not-so-funny noises.
Electros in the signal path tend to have an easier life and are normally much less of a problem. Naturally if you significantly change the values of caps in the tonestack or coupling between stages this will have some effect on the amp bandwidth, but before we get too excited we need to remember that electrolytic caps have a very wide tolerance on their nominal value, typically -25/+50% (which is one good reason to avoid them in the signal path); but an awful lot of horsefeathers gets talked about capacitors, their dielectrics, and its contribution to "tone".
There is a page somewhere where this topic is picked apart by some real testing of supposed "mojo" caps, "bumblebee", "paper in oil", etc., and concludes that if anything the revered "mojo" caps actually perform worse than new poly caps from Mundane Electronic Suppliers Inc.
When somebody says that they changed some caps for Das Wundercap$ and the tone was greatly improved, you can bet that a) the original cap(s) were actually faulty, or b) they are kidding themselves (and you). And there is an awful lot of (b) about.
More great info guys! Thanks!
There doesn't seem to be any significant hum or noise so I guess these caps are still pretty good. But I'll probably change them out anyway, especially since I plan to keep it.
Thanks again guys! You're the best!
Welp- It was working good there for a while. Fired it up today and there was a lot of static and hum. Sounded OK for a few minutes but then went bad again but the hum was there much louder than I remember it ever being.
I'm assuming given the previous advice that new filter caps are in order.
I did run the preamp through another amp's power-in jack and there is no static. But there is still a fair amount of hum.
I opened it up and checked the resoldered joint but it didn't seem to be the problem. Nothing stopped the static once it started. No cutting in and out. Just once it starts it doesn't go away.
Any advice on what kind of caps to get and/or if I should replace anything else while I'm at it?
Thanks.
Chewy.
Well I believe those are 6000uf 50v electrolytic caps(look on your caps and confirm). You will not find 6000uf caps as that is not a standard used today. Meaning you will have the choice of using 4700uf 5600uf or 6800uf caps. When I recapped a Randall RG80 I went with the 6800uf caps to add some extra filtering. I have read opinions that on filter caps it is better to go up rather than down, when picking an alternate farad rating. Either way it will work with 5600uf or 6800uf...
Here are the ones that I used...
http://www.mouser.com/ProductDetail/Nichicon/LGU1H682MELC/?qs=sGAEpiMZZMtZ1n0r9vR22ctH%2f%2fowniwfqbmxvr0mMJ4%3d
Edit: Meant to type 5600uf as the low figure...
I previously suggested that the cap you worked on may have actually had an intermittent internal connection and the fact that you now have hum and crackles still points in that direction, so I'd now do all five of those larger electros while you are at it - the two cans and the three biggies on the PCB.
Thanks DrGonz.
:)
+1 to Roly! Yeah I also changed some of the other larger sized electrolytic caps while I had the amp open.
thanks Roly and Dr. Gonz.
Ordered the big caps suggested above and picked up the three smaller ones at a local electronics supply store.
Fixin' to do some fixin'! :dbtu:
I replaced all those caps- and other than it being not the neatest job in the world, it seems to be working great! I'm running it right now with an iPod- been going for about 30 minutes and sounds good.
I'll re-case it in a few hours if it doesn't show any signs of problems.
Thanks again guys. You're the best!
Chews.
:dbtu:
Well time will tell, but you can prove the point by measuring each old cap's leakage, and effective capacitance by CR time constant charge/discharge.
And when you are working on "mission-critical" equipment, it's nice to be really sure.
A good tech should be able to re-create most faults on demand if they really understood what was going on/wrong and has really fixed, or at least be able to do a coherent write-up.