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Post subject: Power supply vs CPU (more dropoiut issue ideas)
Posted: Wed Nov 13, 2019 12:08 pm
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Aspiring Musician
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As i said in another thread i installed the fan. It's pointed at the CPU on an angle so that some air hits the PSU too. But it's not a lot of air on the PSU. Anyways, i started thinking about having put a house fan on the rear of the amp when the dropout issue was happening and within a minute the issue faded till it was gone. It hit me just now that feeling the back of the amp, where the PSU is it gets pretty warm while the area where the CPU is doesn't. And the PSU board is parallel to the back panel while the CPU is parallel to the bottom of the chassis. So it seems to make sense that a fan pointed at the back of the amp would not have cooled the CPU to any degree in one minute. That makes me wonder if it;s not the PSU that was cooled by the house fan and therefore stopped the dropout issue. I can't think of a reason the PSU would cause it, but then my electronic theory is pretty minimal. The only thing i can imagine is if it gets too hot maybe it could change the voltage to the cpu or other component that may then cause the dropouts. I know there are regulators so that shouldn't happen, tho maybe the regulator itself is failing when hot. I dunno. But the point is i don't see how the fan on the back of the amp could have cooled the CPU that fast due to it;s location and the fact the chassis shows very little heat in that area but a lot of heat where the PSU is.

I just thought to post this and see what ideas this might generate. I'd of course especially like to hear from Tim who seems to have the most knowledge here. I'm just wondering if i might be better off repositioning the internal fan i installed yesterday on the PSU side instead. By the way, my digital thermometer shows the fan has dropped the temp of the heat sink on the CPU by 15 degrees fahrenheit as opposed to w/o the fan. Went from 100 to 85.


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Post subject: Re: Power supply vs CPU (more dropoiut issue ideas)
Posted: Tue Nov 19, 2019 1:55 pm
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Professional Musician
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Joined: Thu Aug 07, 2014 3:25 pm
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As I suggested previously, Freeze spray is the tool of choice to find the kinds of intermittents you describe. the spray can locate the area. Freezing a flattened q-tip can apply the cold to specific components in the sensitive area.
Be cautious when poking around in the power supply. The main cap can hold a high voltage even after switching it off and unplugging it.
Switching power supplies are hard on electrolytic capacitors due to the high switching frequencies. You should look at those if the soldering is stable. Look for rounded tops on the electrolytics that indicate venting. Also, look under the caps to ensure the rubber bottom seals haven't leaked. But you should know that they can fail without any visible trace.
As a matter of maintenance, when a capacitor in a switching supply wears out normally, it is an indicator that the rest of the caps may be getting weary as well. This is one of the reasons for the 5 year warranty and no repair option. It get to whack-a-mole unless you replace all the caps. This is not a Fender problem alone. Every switching supply has the same future. :(
Another general issue for combo amps is fracturing leads due to speaker vibrations. This usually occurs on transistors and diodes that are mounted to heat sinks. When inspecting any of these, you should actually tug or push on the leads. You can't see fractures and you can't really measure them in a static state. Heat can inflame them, though.
On switching supplies, add to the list the wires on the donut inductors, transformer leads, and any other lead that is connected to 2 large parts.
Good luck


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Post subject: Re: Power supply vs CPU (more dropoiut issue ideas)
Posted: Tue Nov 19, 2019 11:23 pm
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Aspiring Musician
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I understand all that and have troubleshot many PSUs and other circuits with both freeze spray and checking caps as u describe and checking leads etc etc. Like i have already said several times tho, i am quite sure this isn't an issue like that given so many here and elsewhere have described this issue. The way it manifests just doesn't jive with any of those issue and i am quite sure it's a design flaw, likely dealing with heat after that test with the house fan. In fact, since the 2nd to last time i opened it it stopped dropping out. Hasn't done it once and thats been a couple weeks when it was doing it 1 or more times per day. I have no idea what could have changed but i only opened it up to see what i might do to expand the heat sink. It hasn't done it since but i still opened it again and put a fan in it. It's on a switch and i have just left it off since it's not been acting up, and i figured this would be a good test....switch it on next time it starts and see if the fan stops it as well as the house fan did that day i tried that. But i haven't have the opportunity to test it since it's been working perfect. crazy huh? It's like the amp is F'ing with me ! If i removed the fan it will likely start again. :mrgreen: Maybe when i opened it and moved some ribbons around it changed the way air circulates in the amp, who knows. In any case if it does anything at all abnormal be it dropouts of tone issues i will switch in the fan and see if that helps.


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Post subject: Re: Power supply vs CPU (more dropoiut issue ideas)
Posted: Wed Nov 20, 2019 9:21 am
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Professional Musician
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There are any number of ways to chase away a symptom.
If it is a manufacturing defect, chances are that it is a failure of the Lead free solder.
A failing component usually fails and doesn't get better. It's condition worsens.
If the power supply drops out, it will reset the digital section. If you put a heavy load on the amp, the draw on the PS will increase the chances of a dropout. That could account for the low volume symptom. Power supply instabilities can cause all sorts of weird problems.


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Post subject: Re: Power supply vs CPU (more dropoiut issue ideas)
Posted: Wed Nov 20, 2019 10:22 am
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Aspiring Musician
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Well, the one thing that's clear is the one and only time the symptom ever went away without rebooting was when i put a fan blowing on the back panel. So it has got to be heat related. Whether that's due to a failure or not i dunno but i doubt it given the many with the same issue. It may be the PSU is just not adequate and at times it heats up enough to cause issues. Or as first thought it may be the CPU and a lack of adequate cooling due to an inadequate heat sink or whatever.

I'm no stranger to bad connectors and solder joints, believe me. And i do realize how illogical some issues can seem. But once when i occurred i chopsticked the living H out of everything in that chassis ad nausium and nothing affected it. Not that i haven't witnessed that before where it turned out to be a bad joint after all, but in most cases if u chopstick the thing to death like i did it will trigger it or stop it. In any case, i have troubleshot amps since the 70s and my instincts plus the facts tell me this is a design issue. But right now the amp just has not been doing it at all so i may never figure it out. If it starts again i'll switch the fan on and that should be a bit more telling with whatever the results of that are.


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Post subject: Re: Power supply vs CPU (more dropoiut issue ideas)
Posted: Thu Nov 21, 2019 8:31 pm
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Professional Musician
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I have been troubleshooting for a similar amount of time and have just come to accept that sometimes I will find myself working on the wrong end of the horse. I have been humbled time and again by what I don't know. The mysteries of the unknown are deep until you come up with the simple explanation. Your probing will eventually come up with the correct answer and you can set all the theories aside.
My mentor, E.E.E always said to think simple, not to overcomplicate a symptom. He was seldom wrong.
The fact that the unit is now stable proves there aren't any failing parts. Bad parts don't get better. Bad software doesn't get better.
That leaves connection problems. Bad solder, through holes, or connectors. These types of intermittents are smoked out by thermal stresses. Cold soaking overnight. A hair dryer on the circuit board. A chopstick won't find a bad through hole. It won't stress the pins of a surface mount IC. Get some hot and cold in there and make that sucker talk. Yer halfway there with the fan...


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Post subject: Re: Power supply vs CPU (more dropoiut issue ideas)
Posted: Thu Nov 21, 2019 11:23 pm
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Aspiring Musician
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The hair dryer idea is good, i'll keep that in mind if i need to TS it again. But at this point the thing is not only not dropping out, but the tone has been more consistent than it's ever been. Really strange. So i don't even wanna look at it wrong let alone pull the chassis and mess with it till it starts again.

I too have been humbled by some issues that have made absolutely no sense at all. This one isn't that bad, as there are several possibilities. But they are elusive. Bad joints in surface mount components the size of a amoeba are hard to find and hard to repair even with a magnifier. PSU issues are easy but the rest in an amp like this ain't fun. So amps like this are a real pain.


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Post subject: Re: Power supply vs CPU (more dropoiut issue ideas)
Posted: Fri Nov 22, 2019 5:27 pm
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Aspiring Musician
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It finally started dropping out today for the first time in a couple weeks and the first time since i installed the fan. As i said b4 i keep the fan off and was waiting till the issue started so i could turn the fan on and see if it stops it. It did, but it took 3-4 minutes unlike when i put a house fan aimed at the back panel which stopped it in 1 minute. At a gig i would leave it on always but at home it's not a big deal if the issue happens, so i don't use it. I imagine it would keep this from ever happening if i left it on always. But because i leave the amp on all day at home due to the long startup time, i wouldn't want the fan on all day. I just don't need the thing dropping out at a event of any kind. I still think it may be best to have it on the PSU, so i may move it next time I have the chassis out. I have a gut feeling it may be the PSU triggering and causing the issue in the CPU.


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Post subject: Re: Power supply vs CPU (more dropoiut issue ideas)
Posted: Sat Nov 23, 2019 10:40 am
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Aspiring Musician
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Very interesting update. It started again today, so it's apparently back to being a daily event. This tim i turned the fan on and no change after 5 minutes. Had the handle screws out so i can get in there instantly and i took the handle off which leaves a large opening thru which to play around with things, and i put a small house fan on it. Still no change. Now, while i have done this is the past, i started chopsticking it thru the to and when i moved a ribbon cable it stopped. Continued on and was able to recreate and stop the issue. So what fender said about it being a ribbon cable may be correct after all. But the questions are, why then has at least one new owner still have the issue when he just got his recently. Fender said they recified this after all. Well, maybe he bought one that was new old stock? Also, i have chopsticked this amp b4 with no luck. So who knows. In any case i am going to pull the chassis and fix that cable. I can either hardwire it or fix the cable itself, and i know how to fix that type. They have snap on ends that pierce each wire so you have to cut a bit of the end off and snap on the connector to fresh ribbon. Not reliable tho so i may do a hardwire fix. Plus on end i think is NOT snap on, i have to get in there and just see. Anyways i will report back then again after a long enough time that i can be sure it's fixed.


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Post subject: Re: Power supply vs CPU (more dropoiut issue ideas)
Posted: Sat Nov 23, 2019 11:12 am
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Aspiring Musician
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Geez....this is getting to be a PITA. Pulled chassis, pulled and pushed that ribbon ad nausium and nothing. Whats worse is i can see it would be insanely hard to hardwire it, especially the end that terminates on the control board which is not a pull off connector even tho it;s also a snap on. So gonna play around in there for a bit more and if i can't find it i'll just deoxit the end that comes off and pray. As much as i love this amp i just think i'm not willing to go this much further. Especially when i now don't know if that cable is the issue even tho it appeared to definately be just an hour ago. As Al Bundy used to say, ARRRRRRG!


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Post subject: Re: Power supply vs CPU (more dropoiut issue ideas)
Posted: Sat Nov 23, 2019 12:13 pm
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Aspiring Musician
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Couldn't just let it go. I'm doing one side, the one on the CPU board that pulls off. Removed the end and i'm in the TEDIOUS process of soldering every wire to each pin. Made even more rtedious in the fact you have to take time and be very careful that each wire is soldered well which is a major PITA and requires a eye loupe magnifier. I decided to take a break and post this pic. If it continues to dropout after this i will do the other end.
Image


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Post subject: Re: Power supply vs CPU (more dropoiut issue ideas)
Posted: Sat Nov 23, 2019 12:30 pm
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Professional Musician
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oczad wrote:
But because i leave the amp on all day at home due to the long startup time,

Wait... You leave your amp turned on 24/7, or just when you are using it?????

_________________
-- Rich


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Post subject: Re: Power supply vs CPU (more dropoiut issue ideas)
Posted: Sat Nov 23, 2019 12:54 pm
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Aspiring Musician
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most waking hours. From probably 10 am to 8 pm if i know i will be home all day.
Anyways, deed is done amp back together and now we shall see if the issue is gone and like i said if not i will do the other end.


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Post subject: Re: Power supply vs CPU (more dropoiut issue ideas)
Posted: Mon Nov 25, 2019 6:48 pm
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Thought fan/circulation was the fix for a little while but sadly not. Though disabling WIFI and BT on the amp has stopped my dropouts thus far.


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Post subject: Re: Power supply vs CPU (more dropoiut issue ideas)
Posted: Mon Nov 25, 2019 9:46 pm
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Aspiring Musician
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That's 2 of us that thought it was heat related only to be disappointed. We'll see how this connector fix fares. Fender did say it was a ribbon cable issue so maybe that's it. Theres one other ribbon cable but the one i fixed was the one that seemed to start and stop the issue when i chopsticked it the other day. So we shall see. So far after a coupe days asn't done it yet. Of course if that's it many owners will unfortunately not be able to do the fix i did.


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