I've got a Trademark 60 that sounds amazing!!! However after 15 minutes she shuts down.
1) Caps?
2) OP Amps?
3) Cold Solder joints?
4) OT?
Any one who can point me in the right direction would be awarded with two thumbs up :dbtu:
is anything getting overly hot? DO power supply voltages remain or go?
What does "shut down" mean? All signs of life go off? Lights stay but sound goes? Display freezes?
1) Caps? - unlikely
2) OP Amps? - unlikely
3) Cold Solder joints? - unlikely
4) OT? - highly unlikely; it appears to be solid state and therefore almost certainly won't have an output transformer.
Guessing doesn't work.
First we identify what is actually wrong, then we fix that.
Being solid state my first guess from your definite "after 15 minutes she shuts down" (which I assume is 15 mins of flog, not just sitting idle or quietly noodling) would be that it has a thermal cutout. If it isn't getting hot internally there is still a chance that a thermal cutout itself has gone faulty and operating at a lower temperature.
Being a 60 watt amp with no obvious heatsink, and only a tiny vent on the back, reinforces my view. I wouldn't build an amp like this without a fan (but then I wouldn't build a 60 watt amp in this manner).
Does it come alive again if left to cool down?
Are you running it straight, or have you added an external speaker cab?
Please pull the chassis an post a couple of overviews of the internals.
Quote from: Roly on May 06, 2014, 03:46:52 AM
...I wouldn't build an amp like this without a fan (but then I wouldn't build a 60 watt amp in this manner).
Interesting you say this as I've always been curious to try out one of these amps. How would you build one/do it differently?
So the heatsink(s) can breathe.
An early incarnation of my Twin-50 with three Mullard 55D heatsinks on the back;
(http://www.ozvalveamps.org/playmaster/pm125.jpg)
A heatsink is not a magic devices that makes heat simply vanish, it's a coupler to the air, and if the air it is coupled to is trapped inside a chassis then all that is going to happen is that the whole shebang is going to get muther-hot.
It is a common design error to under-estimate the amount of heatsinking required, driven by the facts that heatsinks tend to be expensive, and mounting them properly, fins vertical in free air, can be difficult or conflict with a desired overall layout or look. I have struck this thermal "optimalism" so often in commercial gear it's not funny - e.g. a steel chassis makes a truly lousy heatsink (and even an ali one isn't much better).
And they are rated to operate in 25 degree C free air, not confined inside a box. You can model heat in sims like LTSpice and it requires a thermal gradient (like a voltage gradient) for heat to flow (like current) from the chip to the case, case to heatsink, heatsink to ambient air - if the air is, say, 65C, then everything back to the chip dice will be hotter still.
In this case there seems to be only one tiny little vent to get rid of about 60 watts worth of waste heat (60W amp, 50% efficient), and I suspect that the ultimate answer here will be to fit a small fan over that vent inside to draw in cool air.
It might be easier to visualise if you imagine that chassis with a 60 watt light globe belting away inside.
Hi Guys, thanks for the questions. The amp does not power off after 15 minutes (all lights are still on) but the amp "farts" and then output stops. Then if I turn off the power switch off/on it powers back up.
Take a look at some pics i've attached
Those are nice detailed shots, but not an internal overview.
1 - Okay, let's try this another way - is there a round capsule (thermal cutout), about 5/8ths inch in diameter, with two leads coming off, attached to the heatsink somewhere?
2 - How hard are you hitting it when the fault happens?
3 - Is it always about 15 (+/-5) mins, or sometimes much longer or shorter time?
4 - How hot is the amp getting (back, near vent)?
5 - Does it still play up if just left idle for half an hour or more?
6 - Are you driving an external cab?
7 - Does it *always* recover on power down/up?
Try running it with the chassis out and open and see if it does the same thing.
The amp still operates outside of the cabinet, even with the "cooler temp" out of the cabinet it still shuts down. As far as a (thermal cutout) the design didn't include one in the layout of the amp (poor oversight).
I expect this amp uses the LM3886 IC which has a heat sensor/thermal cutout built in. The symptoms you are getting points to this shutting down.
In the picture raul.jpg what is the brown material under the IC under the metal clip? Looks like cardboard?
Tony - in another forum a member noted that the Part Number is LM3876T and that when he swapped it, the problem went away. But you think it could possibley be a LM3886?
And yes it appears to be cardboard from factory, to maybe protect against grounding out?
Thanks
B
If it is cardboard, then there's your problem. It should be a special silicone rubber/fibreglass washer (Sil-pad) to transmit the heat. Cardboard is a heat insulator!
LM3876 or 3886 there's not much difference between them. They have similar pin-outs, but 3876 is 56W and 3886 is 68W outputs. Both will shut down if overheated.
Tony - I'll check what it is when I pull it and replace appropriately
Thanks!
The output chip in your amp is the LM3876T and it is available from Digikey for $2.75 without shipping. There is a "pad" that Tech 21 puts on the heatsink to keep the backside pad on the chip from shorting to the heatsink (chassis ground). If you have an IR thermometer you can check the temperture rise on the device to see what is happening. Most if not all of this board is surface mount technology (I don't remember seeing anything smaller than 0805).
Heatsinks are interesting creatures - I have seen several demos using FEA to show that there is a "diminishing point of return" on the number of fins needed for a given application. Not enough and there is a lack of heat transfer and too many (or wrong geometry) and you get turbulence that diminishes heat flow....
I'll be interested to see/hear what happens...I've been itching for some Tech 21 gear and its always good to know what I'd be getting myself into :-)
Like Tony I'm also suspecting thermal shutdown of the power output chip, but from the pic it looks like an impregnated thermal pad to me, and if it were really cardboard I don't think it would run for 15 seconds never mind 15 minutes.
Just a tip bogner100b, I'm a tech, but you are my eyes and ears, and if you don't actually answer the questions that are asked I/we are operating blindfolded and confined to guesswork.
It's still doing it when the case is open, but how hot is the heatsink getting (cool/warm/hot/untouchable)?
Direct a fan into the innards so it has bulk cooling air and see if that makes any difference.
gbono
Done a lot of experiments with heatsinks. When depending on convection alone the air right next to the fins has to get quite hot before it moves out of the way to allow cooler air to have contact. This explains why there is such a large difference between fins vertical and fins horizontal. Even the smallest forced draft has a profound effect, and in fact the difference between a gentle breeze and a howling gale is less than from still air to a gentle breeze. This leads to the rule of thumb with fans that 90% of the cooling effect come in the first 10% of the rev range.
http://www.ozvalveamps.org/techsite/thermofan/thermofan.htm (http://www.ozvalveamps.org/techsite/thermofan/thermofan.htm)
I've used a ton of Tech 21 stuff over the years.
A common fix on the Trademark 60 is to patch around the channel switcher with a 1/4" cord in the effects loop (out the pre - into the power). You don't even need to select with a footswitch.
See if that restores the sound.
I've seen this happen on TM 60's with a lot of time and humid environment exposure.
Yeah I would have tried the patching of the effects loop just to rule it out. Since this fault is occurring in a timed fashioned then maybe it is related to the thermal cutout issue. However, Roly asked many many questions that were never answered. I mean was the heat sink getting hot? Not much troubleshooting going on in this case.
Hi Guys - So I replaced the output chip ( LM3876T), fired it up........played for 5 minutes...and same thing POWER DROP out. :-[
You should really go through the thread and test the things folks have asked you to. Once you provide answers to those questions, we will be able to help.
Chik-chik
BOOM!... bugger ... missed.
I'm not having a good day. An old friend turned up with his 'puter, can't access anything, wants to unload his large collection of photographs. Now he's a really nice guy, great drummer, good blues harp player, but he's a total techno-illiterate.
Fire it up and this old clunker is asking for Windows authorisation. WTF?
Turns out the 14yo son of his new girlfriend has been having a go, after all aren't all teen dweebs Masters of Computer Science?
I've been telling him for some years now to disable the password protection. He doesn't need it and the potential downside...
Give it a badly needed clean and switch to a known good bootable HDD of mine, and everything is fine, so the basic hardware seems okay.
Alright, out with his HDD and into one of my machines as a slave. It's so full you couldn't get a prawn cracker on there, but all goes well until I try and access his data folders and ... it's all compressed
and encrypted! If I had warned him once I have warned him a dozen times over several years, but no, here we now stand at last, knee deep in the ordure.
It appears that the only way in is to put his HDD back and try and get his machine to boot. Replace dead CMOS battery and reassemble. It wants an Internet connection to do the validation, but seems to be at such a primitive stage of booting that it won't recognise any of the connections I offer; looks like it will only work with his old ADSL connection (which got left at his previous house blah blah), and which, of course, I don't have.
Waste another hour trying to get some sense from Microsoft's phone robot, or talk to an actual person, then the working day ends and that door closes.
He tries ringing the 14yo to see if we can get some sort of handle on what he may have done to get into this situation but gets the girlfriend who tells him, loud enough for me to hear, that he should "take it to a
real technician".
A working lifetime on a wide range of electronics and unbogging hundreds of computers flashes before my eyes and I'm filled with a homicidal rage, which I somehow manage to contain because she is not actually to hand for a spot of strangulation. He is in this situation because he a) failed to follow my repeated advice, and b) let a 14yo play with the machine containing his valuable collection of photographs.
{and lightning bolts have nothing on hormonal teens when it comes to turning a functioning computer into smoking rubble. One red-faced mom called me to the family computer which now had highly gynecological wallpaper locked in and was literally trying to call Nigeria long-distance.}
After four hours I intended to use sorting a problem on one of my own computers, having to accept that this is one of the 1% of jobs I can't fix due to the "monkey grip" or keys-locked-in-the-car nature of the problem, I get grievously insulted after providing a couple of hundred dollars worth of skill at the drop of a hat for nothing. :trouble
I think I'll just have a little lie down now, maybe watch some garbage TV... :duh
Quote from: DrGonz78Not much troubleshooting going on in this case.
Fixed.
Quote from: joecool85 on May 22, 2014, 06:58:54 AM
You should really go through the thread and test the things folks have asked you to. Once you provide answers to those questions, we will be able to help.
We cannot overemphasize this enough. If your car doesn't start one morning, do you automatically replace the engine? Of course not...you would (hopefully) go through some diagnostic steps--does the starter motor turn over, is there gas in the tank, etc.
Same way with amps. Sometimes we open up the amp and the problem is obvious, but often it isn't. If the problem isn't obvious, we typically start going through various troubleshooting steps--we don't just start replacing parts. We measure voltages, trace the signal through the amp, sometimes we observe the signal on a scope. The goal is to determine where the problem lies, then replace only the defective part(s). It's the most efficient, most cost-effective way.
Merely replacing parts can sometimes create even more problems. I've got a friend who sells used stereo equipment and from time to time he brings stuff over to me to repair. Often, he's tried to fix it himself...but his repair skills consist merely of unsoldering parts and replacing them, he has little technical knowledge and no troubleshooting skills. Usually, I've found that he has replaced perfectly good parts. He's also inadvertently soldered transistors in wrong, lifted PCB traces, and had cold solder joints. In other words, by attempting to fix an amp with blind-luck parts change-outs, he's caused more problems than he's solved.
As an owner of a Tech21 Trademark myself, I can confirm what Roly suspects from the design: they get really hot after a good usage. Never had a problem with mine (which actually is a 120 and is monted vertically with a little more vents in it).
anyway, most important thing to do is to LOCATE where the problem lies. Basic trouble shouting for an amp which has such a complete set of connexions on the back panel would be this:
1° try connecting the preamp out (either effect send or Sansamp out) to another power amp/combo amp/whatever amplified thing. Ear if the preamp is good.
2° try feeding the poweramp with any preamp you can find (effect send or preamp out of another guitar amp or even a mp3 player into the effect return of your amp) see if power amp is good
3° try bridging effect send to effect return with a 1/4 cable see if the effect loop switching and connexions are good. Make this try with and without footswitch plugged in.
4° Also try with and without reverb activated.
5° If you have access to an external speaker, also try with one.
Time being a factor, especially on an amp which by design heats a bit more than most others, we can safely thing temperature is a factor. Well temperature is a factor for purposelybuilt thermal cut out, but it is also a factor with bad connexions (connectors OR bad solder joints). You know things tend to move/change dimensions a bit when temperature increases don't you? It isn't that big a stretch to assume a bad connexion may have turned into an unintended thermal cut out. And is the amp farts instead of just going silent, then I would thing an unintended thermal cut out is more likely than a purposely built one. Just saying...
An early thought was that in this particular setup there is something like an extra cab which is resulting in too low a load impedance and thus excessive amp heating, triggering the internal chip protection, but the question never got an answer.
I'll now return to my bench where I'm trying to fix my Crystal Ball.
Been away for a bit but to try and answer a few questions.
1) There is no other cabinet involved with this amp which would lead us to assume that we are dropping the impedance.
2) The amp is still functional it just as noted in other posts fartsquirts out.
3) Turn back on in 10 second and we're good for while then she farts again.
My question is whether or not the PT is shorted out?
Is there a cap that needs replacing?
Quote from: bogner100bMy question is whether or not the PT is shorted out?
The very few facts hat we have been given to go on are not consistent with that diagnosis. No.
Quote from: bogner100bIs there a cap that needs replacing?
Please see
this post (http://www.ssguitar.com/index.php?topic=3466.msg26088#msg26088).
Was this heat related? I am not sure if you answered the question if the heat sink was getting hot? When you first changed the chip you said the amp did play for about 5 minutes. Now it is back to 10 seconds and farts out, turn off then on, 10 seconds farts out again.
This is not going to be easy to fix without a schematic and we will never get one for this amp. Best idea is try to understand the datasheet for that chip and how they use them in circuits. Without testing voltages we definitely can not conclude it's anything related to the PT. Does this amp have power amp in or preamp out jacks? Have you established this testing method in relation to this post?>>>
Quote from: Rusty Chops on May 09, 2014, 12:04:04 AM
I've used a ton of Tech 21 stuff over the years.
A common fix on the Trademark 60 is to patch around the channel switcher with a 1/4" cord in the effects loop (out the pre - into the power). You don't even need to select with a footswitch.
See if that restores the sound.
I've seen this happen on TM 60's with a lot of time and humid environment exposure.
Quote from: bogner100b on June 24, 2014, 12:25:37 AM
Been away for a bit but to try and answer a few questions.
1) There is no other cabinet involved with this amp which would lead us to assume that we are dropping the impedance.
2) The amp is still functional it just as noted in other posts fartsquirts out.
3) Turn back on in 10 second and we're good for while then she farts again.
My question is whether or not the PT is shorted out?
No.
Quote
Is there a cap that needs replacing?
How should we know?
None of your data points to that.
::)
(http://msrayspsychicepisodes.files.wordpress.com/2012/01/crystal-ball-cartoon.jpg)