Help with LED readout please!

Hello.

Can someone please help me decode the LEDs on TM 36 please?

All 4 LEDs are on constantly.
Pressing the readout gives;  11 all flash,  12 1 and 3 flash,  13 1 flashes.

Is it a complete re valve?  Or,  something else?

Thanks in advance!

Alexander

Hi Alexander, welcome to the forum.  One very simple question that needs to be asked is, does the amp actually work?  Usually all 4 LEDs on constantly would indicate a fault such as a blown HT fuse.  If that happens then there is no power supplied to any of the output valves so the amp would be totally silent.  Do you have that situation where the amp gives no sound output at all?

"Pressing the readout gives;  11 all flash,  12 1 and 3 flash,  13 1 flashes."  I think you must mean that there are 11 flashes with all LEDs, then there is a further one with only 1 and 3, then there is another final one with only 1.  If that is correct then your valves are fine.  The difference in LED flash counts between valves in a pair should be no more than 4 flashes for best sound.  The valves are linked in working pairs, the outer 1&4 are a pair and the inner 2&3 a pair.  The LEDs represent the valves in their locations so the left LED represents the left valve and so on.  So you have the following flash count for each valve:  V1=13,  V2=11,  V3=12,  V4=11.  Your pairs match as 1/4=13/11, and 2/3=11/12.  This is fine, your valves read as good and matched within spec.

If all 4 LEDs are on constantly and the valves are fine then it points to something like Standby.  Have you selected "Silent" for the Power Soak on the rear panel?  If you have then press it aqain so all 4 of the Power Soak lights are off.  The amp is then in Normal mode.  When you select any of the 18W, 5W, 1W selections the switch should light up and so will the inner pair of TSC LEDs.  This shows that the inner pair of output valves is now turned off so the maximum power available is basically being halved.  Pressing thePower Soak switch which is currently lit should put the amp back into full power mode and all switch LEDs as well as the TSC LEDs should turn off.

Check the Silent button on the back and make sure it is off. Do you have a copy of the manual for the TM36? It is available online if you don't.

Hey bordonbert,

Thank you for taking the time to reply.  I can see that I should have been clearer!

The amp doesn't work on any setting.  Standby is off.  It broke during a session where the guitarist was driving the gain on the clean stage very hard against a reduced master volume.

You are correct in your description of the LEDs and thank you for explaining that.  I did look in the manual and I thought I understood,  but I'm not an 'amp man',  so I did struggle!

The HT fuse looks like the answer.  I've got the back off at the moment,  but can't see an internal fuse.  Would you happen to know where it is located please?

Thanks,  Alexander.

Yes Alexander I can certainly help with the fuse.  Warnings first, though I'm sure they aren't needed.  LETHAL VOLTAGES ARE INSIDE THE UNIT WHEN IT IS WORKING AND THEY REMAIN FOR A SHORT WHILE AFTER SWITCH OFF.  Make sure to not touch anything you don't need to.  There is no need to fear working in there if you take the right precautions.

First, switch off the amp and remove the mains lead from the back.  Switching off the power is not enough, always remove the lead.

Second, wait for a couple of minutes before going in.  This allows the power line drain resistors to make sure the HT line has been bled down to a very low and safe voltage close to 0V.

Ok, now I feel better having pointed that out, on to the fuse.  I have full service info on the GM36 and on the TM18.  The TM36 hasn't escaped into the wild so I don't have that but...  There is a strong family llineage in these amps.  They all share a similar base circuitry configuration.  I'll post the GM36 and TM18 info and your own will be similar to at least one of them. The top picture is the TM18 and the bottom is the GM36 so you can compare.

The amps all have a number of overlapping PCBs inside, that's how they get to be so small.  The fuses sit on the mainboards of both amps and should be easily available.  At one end of the PCB there will be a lot of heavy mains wiring and the fuse sits in amongst that.  There will be more than one fuse as the LT circuitry has its own power supply.  You will have to pop them out and check them by either substituting or by metering them - it is NOT enough to do it "by eye".  You cannot test them in circuit either.  Get them out, but check them one at a time.  You can't mix them up that way.

Fuses often blow inside their end caps where you can't see it.  It is essential to check them for continuity with some sort of measuring setup to be absolutely sure they are working.  This can be a dedicated resistance meter or a temporary lash up of battery and torch.  If you have a couple of wires which you hold onto the battery and onto a bulb you can include the fuse in the circuit too.  If the bulb lights up then the fuse is working.  Even this test is not failsafe as very occasionally fuses can break and not part until they heat up in each use.  Just swapping for a new fuse until you see if that fixes the problem is cheap and surefire!

After a few minutes there should be no high voltage left in the amp anywhere, H&K are very good at including safety circuitry like drain resistors.  You can handle the fuses in place but you really only need to gently lever them out for testing with a small screwdriver or similar.  Just popping them back in by hand is fine.  I'm pretty sure the value for your TM36 should be the same as the GM36 which is T400mAL/250V.  The TM18 is only 200mA which you would expect for half the power.  They are both labelled FU1, yours may differ but I would be surprised if it did.  So that is a Time Delay 400milliamp fuse with 250V minimum rating.

Make sure to get the correct size fuse as well as the value.  You should need European 5x20mm fuses according to the other models.  Once you get the fuse out you can read its current value and size on its end cap.  It may have been the wrong value or it may have just aged and popped through weakening so it may not indicate a fault.

Check it out and let us know how you get on.

Great!

May I be clear on something please?

I need to remove the tubes,  remove all the screws housing the frame that hold the circuit board,  transformers and valves,  to get to the circuit behind the front panel where the fuses are?

Thanks

No, don't remove the end cheeks or the top cover or the valves, is should be absolutely unnecessary.  You are only trying to remove the bottom cover.  Here are the steps you need to take:

Loosen the screws on ONE of the end cheeks only a few turns, don't take them out.  This will allow the end cheek to move slightly off the bottom cover lip at one end.

Remove the 10 screws (I think it will be 10) holding the bottom cover on.  Note that a couple of them have lock washers on them.  Keep these and put them back in the same holes.

Move the bottom cover a little to the side to release the lip at one end.  It will then lift off.

I have attached a picture of my own GM36 with its bottom plate removed.  You can see the fine lip on the end of the cover ringed red.  You can see that I have not removed anything else to do that.  The screws on the right hand cheek are showing outside of the plastic cover because they have been loosened, but only a few turns.  That is all you need to remove.

Thank you again for your reply!

I see you have the stand alone amp. Mine is the TM 36 Combo. Again, I should have been clearer!

Are you aware of a simple way to get behind the front panel without removing the entire chassis?!

Oh dear.  That makes a huge difference!  Ok, the combo.  Well there is very little info available for the combo side of the TM and GM series.  No one seems to have problems with them that they try to fix so finding details of how to go about things is pretty difficult.  I have only played one once in my life, (that great experience made me buy my first TM36 and then my GM36 head).  I don't think I can offer any more useful input here, except that I have heard that it is a bit of a tortuous procedure to open up the combos.

I'm still not convinced that getting behind the front panel is the answer.  The fuses will sit inside the chassis and I'm pretty sure that means removing it from the case to get into the cavity.  I found a little info re the TM18 combo.  In a previous post someone solved his own problem with that version.  His was the only post in his thread so you can see how thin on the ground details are.  Here is what he said.

64ironhead wrote: I resolved my problem and updating so others can gain access for tube replacements on the TB 18 Combo.

Removed the six rear panel screws along with the two bolts from the top rear corner brackets.  With sufficient steady force, I lifted up on the edges of the rear panel until the entire assembly began to move.  Continued that upward lift force until the entire assembly became free.  I disconnected the speaker wires from the speaker terminals and removed the amp from the cabinet.

Does that appear to be the same for your own version?  I'm sure he didn't need to remove the whole chassis to change the valves, removing the back panel should have been enough, but as he has done it he could then get to the fuses as well.

Does anyone else have any info they can offer here?

I've looked at pictures of the TM36 combo online. I'm guessing but here is what I would do. I'm pretty sure this will get you most of the way if not all of it.

There are 4 recessed screws in the top panel. These hold the amplifier chassis in the case. The amp is the same chassis as the head, it just hangs upside down in the combo. If you look at pictures of the two models you will see that the controls are all reversed between them. It is much shorter than the actual wooden enclosure so it cannot have more screws than that holding it in place. You will have to remove the wooden back panel to reveal the speaker and amp chassis and allow access to slide it out. It is stuck in place so takes some careful and gentle levering to break the seal. A wide bladed implement like a wallpaper scraper is much better for this than a thin screwdriver which will notch the edge of the wooden cabinet under pressure. Then you simply remove those 4 screws on the top panel and the chassis should come free. The chassis is a fully enclosed box shape so getting into the cavity from the front is absolutely not an option. The only way is to remove it completely as I have described.

Yup. Looks like it. And, the quote from the other guy is the same for me, too.

I'll get on this tomorrow! Will report back!

I finally get round to sorting this. The entire amp assembly need to be removed and the cover removed to access the fuses. A strangely awkward place to put a fuse!

Thank you again for your help.

Al

That's strange!  All of the H&K amps I have ever seen have the fuses accessible with only the bottom cover plate removed.  No further breakdown should be necessary.  Here is a picture of a TM36 from underneath in that state.  Though you can't see it clearly that ledge along the bottom of the pic below the pots is actually the lip of the chassis.  All of those PCBs are still in place and you can see the fuses on the right.  They should only have needed hooking out of their holders with a chopstick or electrician's screwdriver.  You don't even need to take off the top cover to do this, you only need to loosen one of the end cheeks a touch to slide the bottom cover from underneath it and off.

Never mind, the important thing is that you got it working.  I'm glad it's fixed and thanks for getting back and telling us. So get on and thrash it now, that is what it was made for.

Yup. See attached!

I mean that what you have removed there is not just the usual flat plain bottom cover, it looks more like the top cover which is a two faced 90deg angled part.  I've never seen a TM36 like that!

This is REALLY odd.  In your picture you seem to have your rearboard and mains socket mounted on a separate panel which in turn must mount on the main chassis and looks like it perhaps acts as the bottom cover too.  And you have slotted metal end flaps sitting at the end of the chassis profile.  The TM36 just doesn't have that nowadays.  The chassis is usually a simple U-profile with no separate front and rear panels, all controls and sockets mount directly onto the chassis U-shape.  I can't find a genuine TM36 but I've attached a breakdown picture of the GM36 from its manual which shows this.  The TM18 which I have the same info for is also identical in structure, these details in the picture look exactly the same at first glance.  The TM36 should be the same.  Is yours a really old early model because your picture does not look like that to me?



EDIT:  I'm getting quite doubtful about what we are seeing here.  I can't resolve your picture with what I know about the TM36.  It genuinely looks like a non standard chassis arrangement and that can't be the case surely.  Can you post a clear picture of the bottom of your amp showing the edge of the bottom panel and the rear panel carrying the output sockets and mains socket?  I don't mean strip it down again, just show what the bottom/rear section looks like when it is built back up.  We should be able to see how it strips down from that.

See attached

  Jeez Louise!  What is that?  Is that really a TM36?   The penny drops - my stupidity and my apologies for it Lem.  Of course, you told me you had a combo didn't you?  I fell into advising you about the head.  It's difficult to keep all of the details of every thread in mind over the length of time we need to get to the answer.  The circuitry is exactly the same inside of course, it only matters in terms of the casing and build up.

I see your difficulty.  I had no idea that the combo was such an awkward beast to get at the fuses.  Thanks for that info, it will help others I'm sure.  We have precious few pics of the insides of a combo.  Anything you can post would be helpful.

Link to a bunch of hi rez pics of the HnK TB 36 COMBO: https://we.tl/t-L2xYayJ0PW

Link is good for 7 days.

I've sorted the amp now. I am the second owner of this amp and I did notice that I wasn't the first to dismantle the thing. One screw is missing and another was threaded...

If (when) this happens again, I think I'll move the fuse to outside the housing.

Thank you again for all your help!

Alexander

Great news that things are sorted and up and running.  I find that problems with screws in all makes of amp are a common find.  There is something about your average guitarist that makes him think, if I can screw this up this tight then a bit more MUST be better.  There seems to be no easy answer to repairs when this happens.  In wood such as cabinets I've now discovered the screw in metal inserts which have a very coarse wood thread on the outside and carry a threaded hole for a metal screw inside.  They are a real boon.  The only thing I can suggest for your own problem is either the flat folded speedclip.  That's the type which you slip over the edge of the lip to cover the hole and which has a self tapper hole in it.  Or you could epoxy a nut on the back.  Good practice to tighten a screw into it to pull it against the metal while it dries.  If you have any better ideas please pass them on, I'm definitely not the most experienced metalworker around..

We now have confirmation from you that the fuses in the combo are a fair bit more difficult to get at than in the head.  That's a good new piece of info to be able to pass on and I for one was unaware of that.  Bear in mind that a HT fuse blowing is not an everyday occurrence.  It usually takes a specifically severe output valve fault to cause it to blow, valves simply going soft as they age is not an issue.  That said, when it is needed it is there, but what I mean is that you probably won't need to get in there again for many years if ever again.  The idea of putting HT fuses into a position where they can be accessed outside is not usually a thing manufacturers do, though I am aware of a couple who do it.  Accessing the HT from outside is NOT something you want Beavis and Butthead to be able to do.  Lawsuits follow!  Remember Murphy's Law in all of its forms, "If s**t can happen it will", and then read that as "If someone can possibly do something absolutely dumb and shock themselves, eventually someone will".  I have to say that, as an ex-designer of high grade electronics for use by somewhat cavalier and clumsy staff, (the dumb cack-handed masses, Norwegian sailors at sea on seismic surveys), I would never do it!  But for just myself?  We-e-e-e-ell, ok I would be tempted.   If you do it make sure to take care, it really can creep!

Thanks for those photos, I'm very grateful you took the time to set that up and post them.  That's an absolutely great set and should give us material to help out enormously in the future.  I've got them in store now so you can take them down if it frees up storage.  Now, all the tech stuff aside, get the amp to work again, that was what it was made for.  And pop back now and again to keep us up to speed with how you're living with the TM.