Need help repairing a Boss Katana 50 MK1

[icefire]

So I got a Boss Katana MK1 which works on headphones but there is no output on speaker.

I am not a pro and I don't know an awful lot about electronics but I am good with a soldering iron and generally at DIY stuff So please bear with me...

So here is what I have done up to now:
- Since everything works on headphones I suspected the power amp module. The power amp IC is a TDA7293V chip (datasheet: https://pdf1.alldatasheet.com/datash...S/TDA7293.html)



- The chip doesn't seem to get any power. I measured the following voltages with the amp turned on, speaker connected:

Pin 6 -  0.6V
Pin 7 -  1.6V
Pin 8 -  0.46V
Pin 9 -  2.3V
Pin 10 - 2.3V
Pin 13 - 1.6V
Pin 14 - 0.002V
Pin 15 - 0.46V

I checked the phones jack (just in case, because it mutes the speaker when headphones are connected) but was ok.

I have some suspicion about the Power Control knob (which selects 50W, 25W, 0.5W or standby). It has this specification: RD901F-40-125F-B10K-04D60A. It is supposed to be a 10K pot, but I measure 600 Ohms between pins 1 and 3 (it probably makes no sense to measure the pot while soldered to the circuit board). The resistance between pins 1 and 2 or 2 and 3 changes when I turn the pot though.

Anyway, I found the service manual which describes a so-called test mode, which allows to test the gain and volume knobs as well as the powersoak knob. Well, when I get to the powersoak knob test it doesn't pass it (some LEDs start blinking indicating an error).

Is there a reliable way to test this pot?

Or maybe I am barking up the wrong tree and maybe I should be looking somewhere else? Any help would be appreciated.

Here is the service manual with all circuit diagrams: https://file.io/nknoukycOyoC

[Enzo]

OK, no matter what else MIGHT be wrong, if the power amp IC does not get power supply, it won't function. Fix that first.

[The Dude]

^^^^^^^ Yes, THAT!

Also and FYI; Your link to the service manual says the file has been deleted. If you have the schematic, it would help if you upload it.

[dmeek]

Check your fuses with an Ohmmeter. They look something like this:

[The Dude]

Also, unhook the speaker until you verify that there is no DC on the output. If you find fuses blown, it could be due to a shorted output IC, so check the supply pins of the IC to ground and to each other before applying power. Make sure there are no shorts. If a short exists and you install new fuses, they will just blow again.

[icefire]

^^^^^^^ Yes, THAT!

Also and FYI; Your link to the service manual says the file has been deleted. If you have the schematic, it would help if you upload it.

Ok, sorry for that. I tried exporting the pages of the PDF to images but the quality is not good. So here is a second attempt at uploading the PDF (it is supposed to be good for 30 days): https://easyupload.io/nmcsd8. If it doesn"t work, I also uploaded it to dropbox: https://www.dropbox.com/s/wjuu8ojpq0...anual.pdf?dl=0

Check your fuses with an Ohmmeter. They look something like this:

There is just one glas fuse I could identify but it is ok. Of course, it also can be that I'm too stupid to identify any further fuses, but I couldn't find any on the circuit diagrams as well. The glass fuse is on the mains side, so it is uninteresting for our issue.

Also, unhook the speaker until you verify that there is no DC on the output. If you find fuses blown, it could be due to a shorted output IC, so check the supply pins of the IC to ground and to each other before applying power. Make sure there are no shorts. If a short exists and you install new fuses, they will just blow again.

I measured Pin7 and Pin13 to ground, Pin 8 and Pin15 to ground, as well as Pin 7/13 to 8/15 - no short.


About the power control pot - if it is stuck in "standby" position this would mute the speaker but there would be output on headphones. This is why I thought this might be relevant. But the resistance changes while I rotate the knob so maybe this is not it.

If it is a power issue, maybe something is wrong with the power supply. I managed to identify this voltage regulator:




But I can't seem to figure out where to measure the 6V and 3,3V. Furthermore, all LEDs work as well as everything else on headphones... So my first guess was the the power supply should be ok.

Maybe you could help me with where to start and what to look for...

[dmeek]

Here

[icefire]

Thank you so much. Feel kinda embarrassed now that I have somehow missed them. Fuses F8 and F9 (both of them T1.6A, 250V) seem to be defective. I am not sure blown is the correct word here, because there is resistance between the two pins (in the mega-ohm range) which decreases the longer I keep the multimeter leads connected.

I will get a few replacement fuses tomorrow but of course just replacing the defective fuse without understanding why it got defective in the first place would not bring much. So what do I check next?

[icefire]

Ok, once I desoldered the defective fuses and checked them there was just OL on the multimeter display.
I also desoldered the power amp IC TDA7293V from the circuit board and found out there was a short between pins 15 and 14 and also between 13 and 14.

Ordered a new TDA7293V. Once it arrives I will solder it in place, together with the new fuses and then hope for the best.

[g1]

Ordered a new TDA7293V. Once it arrives I will solder it in place, together with the new fuses and then hope for the best.

Be very careful. These and the 7294's are very easy to ruin before even turned on. Make sure everything on it's board is discharged before you even install it.

[icefire]

Thanks for the advice. So, to translate in the words of an enthusiastic amateur, I discharge all the capacitors I can see (starting with the two fat ones on the power supply unit), solder the fuses, solder the IC, fit all the connectors of the different PCBs, connect the speaker and power on... Right?

[g1]

Yes that should do it.

[icefire]

After waiting a few days for replacement parts I can now confirm that the amp is back in business

Thank you so infinitely much, you saved me a lot of time, money and trouble and made me sooooo happy (you have no idea how much joy I experienced when there was sound again )

On another note: The TDA7293 was screwed down to a humongous aluminum heat dissipation block, so I figured that the chip is producing crazy amounts of heat. So upon reassembly, I applied a thin layer of thermal paste (you know, the one for PC CPUs).

[littlebike]

Not to hijack this thread but does anyone have the schematic/service manual for a Katana 100 mkII?

Issue is no power - no light, nothing.

[Oleh]

I have Katana 100.

Has anyone encountered such a problem?
Fuse F2 burned out. Transistor Q22 (integer) in working condition.
The chain after it is short on the ground, which caused the fuse to fail. How to find short on the main board?