Boss Katana MkI 50 W issues and troubles, again

[MatsEriksson]

Since I've been requested to start a new thread instead of "resurrecting" a 2 year old post, I do it here then.

I don't know if this is appropriate to have as a first post in here ever, but I'll try.
I've bought this one new in 2016, and it served me very well at home as a practicing amp at low volumes. Not ever brought it out live, because it couldn't cut it. So I have not taxed it to the max and cranked it. This fault came all of a sudden, and has not starting to slowly show up, with suspicious behaviour beforehand.

Now here's my recent problem, it has - sort of - "died" on me in the following way:

1. Whenever I turn it on, just by flicking the on/off switch, a loud tone (not ground failure note with buzz) at about 50-60 Hz is heard although the switch selector is set to standby and every other knob, volume, eq's are set to zero. No output from headphone jack or auxillary at the back. No changes is heard in sound whatever knob I turn, the power selector (from standby to anything) or volume or else.

2. The tone is heard about full volume, as I can't stand next to it without using headphone like ear protections (like those used by construction builders). I can rotate all knobs without anything changing. Stale and consistent volume and tone.

3. The tone is more sinus wave like than the "ground failure" one with added harmonic buzz. After a minute it starts to tick, and slowly fades away until it becomes dead silent after say 2 and a half minute. No smell at all, as indicating overheating.

I've downloaded the Service Manual (for the Mark1) as displayed here (in that other thread) and tried to fail search it to no avail. I just wonder if someone else has had the exact same problem? I have tried to do a search in here first but no one seemed to have the exact same problem. As it is, I think I should change out a couple of components, as suggested and done before in this post, but I really think something is under-dimensioned for it all, because I think this would happen again. Some components might be too sensitive to over heating.

Maybe this is a "Boss service center only fix" or? About the cost as a brand new amp again?

EDIT: I have soldering skills, and multi-meter skills.

[Mick Bailey]

Someone else may have the same symptom, but not necessarily the same problem.

The first thing is not to run it with the speaker connected. Disconnect the speaker and connect your DMM to the speaker leads and check for any DC. If one rail of the main PSU is missing, the output could be swinging to the opposite rail and put DC on the output, or you may have an output IC failure. The ticking could be the PSU repeatedly trying to restart. Check the main +/- voltages are present.

Often, if you get the full DC supply being passed to the speaker load, it places a heavy demand on the supply and the filter caps can't handle this so you get high ripple which is heard as the loud hum.

Edit: It's not a good idea to replace components unless you know them to be faulty.

[MatsEriksson]

Thank you, I'll check on that immediately. Thank you, will return.

[MatsEriksson]

Proper current enters the main board, until after those two "un-pop" fuses. One of them reads 27.8 volt and the other is ... nil. Which apparently, and luckily, means that not too much voltage enter the chips and destroys them. The "glass fuse" is ok though. Will continue fail searching after weekend. We did connect to a speaker dummy load, capable of retrieving 300W if needed. I e "connected speakers" to it so to speak. Will return.Was at my friend, who posess an oscilloscope too, if needed, and multiple multimeters.

[MatsEriksson]

This one had gone south, as well as one of the "anti-pop" fuses. Just like in the other thread, which means it seems to be a common failure (after a few years).

I've ordered one new, and the fuse too. Not that big a deal, budget wise.

Now, the important thing. In the future, how does one keep this from happening again? Is something else under-dimensioned to keep something from overheating or sending excess voltage to some components? The cognoscenti aboard on here should know. Too poor heat sink? That aluminium or "steel plate" that this one connects to? Anything else to be wary of?

It was a power-to-speaker issue since I managed to get volume and proper sound out of the phone jack eventually. I e all chips that contains sound presets, and DSP (if any) seemed to work ok, and was not "blown". That would've been a major chore, because those are proprietary from Roland/Boss. I wonder if there's different "bettered" versions that are undisclosed to us, in the same Boss Katana Mk1 50W that we don't know of? It can't be MkII since that one is entirely different. I don't think these kind of issues are remedied with just a firmware update or similar.

[g1]

The output IC does the most work of the amplifier. That is why it is the most common failure point. It is not just for this model of amp, but pretty much all amps that use output IC's.
The MKII may be different, but it still uses the same TDA7293 output IC. If it had a weakness they would have switched to something else.
Make sure you get real TDA7293 from a proper electronics supplier. There are lots of fakes available on amazon and ebay, etc.

[MatsEriksson]

The output IC does the most work of the amplifier. That is why it is the most common failure point. It is not just for this model of amp, but pretty much all amps that use output IC's.
The MKII may be different, but it still uses the same TDA7293 output IC. If it had a weakness they would have switched to something else.
Make sure you get real TDA7293 from a proper electronics supplier. There are lots of fakes available on amazon and ebay, etc.

Yeah, thanks for the heads up, no problem,but they're dime a dozen in my country Sweden, and even at a local shop, here in Malmö, Electrokit, which I buy everything from both over the net, and over the counter whenever I get the time to get there... it's in the outskirts though... but if something from them sucks (DOA) I go there and ram it over their heads... they know me, but it has yet to happen... but anyway, they're well equipped in electronic components.

https://www.electrokit.com/en/

[g1]

One more thing, make sure there is no residual voltage at any trace that connects to the IC before you put it in. These chips are very sensitive and can be blown up before you even turn the power on.