Tubemeister 18 problem

Hello, friends. I do not speak English well, but I'll try. My Tubemeister 18 combos barely audible sound, tsc one led flashes even if I pull it (tubes) out. The chips look good, the fuses too. Express your opinion, I will provide photos and my hands for the experiment. The amplifier is brought from Japan and it seems the seller has done something with a transformer (110 to 220v). Thanks

Hi Mario, welcome to the forum.  The first thing to sort out is that dangerous transformer situation.  We need to know:

1) In which country are you living and using the amp?  What is your mains voltage as we will need to know what you are intending to match it up to?

2) The seller was in Japan which has a mains voltage of 100V.  Do you mean he has changed the amp by replacing the original mains transformer inside the unit?  If that is not the case, was he using the amp with an additional external transformer to change the mains voltage to something else which was the amp's correct voltage, maybe to 220V for a European supplied amp or 120V for an American version?  (I have come across people in the Far East doing this before).

That problem must be sorted out first as it could be a potentially life threatening one.

3) Do you have any spare valves you could use as replacements to test your amp?  In particular a pair of EL84 output valves would help.

Then there is the problem of the flashing TSC led even without valves in place, and the weak sound.  Can you test the output from the Fx Loop Send into another amp?  This would tell us if the preamp section is working.  You say the fuses are ok so there is a good chance that this is the case. Have you checked both fuses, particularly the HT fuse? It is never a good idea to rely on just looking at them, they can look fine but be broken out of sight. You need to test them for continuity with a meter or with a battery and low current bulb.

The problem may well be in the TSC control section and it may need replacement parts to fix it.  I am afraid that, most of the time, when chips blow they do so internally and there is absolutely no sign of a problem outside.  It could be the TSC system has been damaged and it won't be repairable by yourself, only replaceable by an authorised technician.  The regulator chip supplying 5V for that board is a good quality choice and can withstand 45V on its input.  The line it is fed from in the TM18 is 22V so even if that went up when fed from an incorrect mains supply it should still withstand it.  The output valves may not like too high a mains voltage though as their anode voltage would jump severely.  They are EL84s which have a datasheet maximum of 300V but they are running at 390V in the TM18.  This is normal for many guitar amps but they would definitely not like to go above that!  If they have surged due to a higher voltage on their anodes that could damage the valves or even the MOSFETs which are the control element in their cathode.  If it was the MOSFETs then this would need replacement by a technician.

Can you answer the questions above carefully please and we can go from your answers?

Hi bordonbert, if we diagnose it, it will be 90% successful because I did not find a service that will take it, but if I know what to do, I can transfer this knowledge to a person who skillfully handles a soldering iron

1) I live in the far east of Russia, our network voltage 220v.
2) Тhe amplifier was brought from Japan with a voltage of 100V (error in the first message), then in Russia the transformer was modified to work in the 220v network. I do not know the modification technology, but I think this change in the windings...
I have a multimeter (fuses have been checked for continuity), but I have not figured out the transformer yet, it will be checked later. I will place a circuit here, in which points should I check the voltage? I do not understand this circuit, ie at each measurement point there should be + and -, otherwise the multimeter does not work
3) First of all I replaced the EL84 output valves, I changed them in places, but only the left TSC led flashes.
4) I will check the preamp section as it will be possible, but if this is a problem with TSC, how can you exclude this option?




PS: He worked without complaints for 3 months

Good work on those responses Mario, that is helpful.  It definitely sounds to me as if you will first of all have to check out that mains transformer.  According to the TM18 data the mains transformer is a single type, EITHER 100V/120V OR 230V/240V.  It is not a dual voltage type where you can simply rewire it to accept 100V or 230V.  If that has already been done in Russia it would be possible to convert it but that would mean rewinding the whole transformer.  Is that what has been done, the original H&K mains transformer has been rewound to suit your 220V mains?

Assuming that that is the case then I would suggest you start by checking that the transformer gives you the correct voltages at its secondary windings.  I have attached a diagram of the connections to the edge of the board and you can measure the secondary voltages there.  Make sure you check the 6.3V, 17V and 270V with your meter set on AC volts.  It will not matter which probe goes to which of the two terminals for each of those voltages.

You could also measure very carefully the HT voltage of 390V.  You need to set the meter on DC volts for this.  Measure the 390V with your +ve red probe on the JP8 terminal and the -ve black probe on JP13, the one next to it, which is connected to 0V ground.

You should get the 6.3V being fairly accurate and the 17V and 270V being a little less so.  The 390V may also be a little lower than it should be.  If they are all very inaccurate the mains transformer is not working well enough.

Dealing with the TSC circuitry will be very difficult.  Your best approach would be to first check the valves and rule them out, then the output transformer, then the MOSFETs which are in the cathode circuit of each output valve, and if they all prove to be good then you can assume the fault is in the TSC circuit board.  If it is a damaged control chip then there is no fix you can apply to that board yourself without having specialist tools and a lot of experience in soldering.  It is a surface mount board with auto-placed and soldered analogue and digital components.  As I said before, semiconductors can be completely blown inside and show no signs of damage externally.

You have the preamp tests to check out and you can measure the voltages for the mains transformer.  NOW A WARNING - Please be VERY CAREFUL working with the amp exposed like this.  These voltages inside can KILL YOU if you are careless!!!

I'm alive, there's no time now, winter is close)

Glad to hear it. I was worried!

I got the following results:
6.5
290-300
17.7
420
this may be the error of the device

Anode 1,2 (jp3,4) - 410v
Jp1 on rearbord - 0v

I checked with an ohmmeter a audiotransformer: (+) on purple j8. (-) orange and blue jp3,4 - 0 ohms, green and red - infinite resistance Jp 3,1 rear. (+) to red, (-) to green -  0hm, to the rest - infinite resistance.  Picture in the third message. it's broken?

Well, looks like pretty good results Mario.

The first is the 6.5V. That is the heater voltage and needs to be fairly accurate, my reference guru, The Valve Wizard reckons within about 10% of 6.3V is fair and 5% is good if you can. Valves don't like being used with their heaters significantly too hot or too cold, both are bad faults and will kill the valves earlier than they should. So you are at about 3% and that's very good.

The 17.7V is pretty good too. For a low voltage DC supply that would be fine.

Your 290V-300V for the 270V is a little high but should pull down during use as the current increases. That is what is giving rise to the 420V of the HT. It's a little high but not outside what other manufacturers run the same valves at.

That looks as though the mains transformer has been successfully sorted out to me.

Your values for JP3/4 and JP1 are fine too. JP3/4 are the anodes and that is the HT voltage after passing through the outpu transformer primary coil so there will always be a little lost there. JP1 is the output from the transformer and should show no voltage until you play a note, then it will have only an AC voltage on it which is the output signal to the power soak and speaker.

Everything seem to tie up as it should,unless I've missed something and others will check on that I'm sure. (It would be helpful guys?) It is beginning to look as though the problem may be on the TSC board and the usual solution for that is to replace it. It has a few discrete components on there but it is based on a digital microcontroller chip which you would certainly not be able to replace. I think it would now help you to talk to the H&K support department and see what they can recommend about servicing your amp in your area of the world. There is very little more that you can do yourself at this stage. Send them an email explaining what you are seeing and asking what procedure you sahould follow to have it investigated and we will see what their response is. I'm not sure how they would go about supporting you in a location where there may not be an official service agent.

Does that sound sensible?

Ok, thanks, it was a great experience for me, I think I'll do it this way: http://viva-analog.com/tubemeister18-meltdown-fix-mods/

If you really want some serious advice, for God's sake don't listen to that guy! He hasn't really got a clue what he is doing. It's the worst form of bodging plain and simple. He suggests bypassing the cathode Mosfets and installing manual bias? Why for God's sake, it works perfectly. The problems occur when it is damaged by some other fault like a tube going west in a big way. The man really is on a campaign to keep amps in the 1950s.

Bodge!!! wrote:since an ATMEGA88 AVR chip contains maybe 80,000 transistors that’s quite a jump in circuit complexity, beyond the dozen or so tube elements we tend see in typical tube amps …

No it's not, it's a single component and in a pretty simple neat bit of circuitry it removes the need to be constantly adjusting your bias and it reports the state of your valves to you in a remarkable way that no other system can do.

You can of course follow his advice, it's your amp, but you will never end up with a reliable amp that way and you will could well alter the sound subtly. I really strongly urge your to drop that stupid site and repair the amp properly to its original state.