Much lower volume on lead selection

New guy here and thanks to all of you in advance!!!I have a used switchblade 50 TSC combo and love it.The problem is the lead selection is much lower in volume than the rest. I tried resetting to factory specs with no difference. Did I reset incorrectly? Is this a common problem. Can any one put me in the right direction to solve this?

Hi Stoney. Welcome and let's see if we can help.

I've pulled in the Service Docs for the Switchblade and, thankfully, it looks very "H&K". Clearing up a couple of points first. When you say the Lead volume is low I assume you mean in relation to all the others? That would mean that the Clean, Crunch and Ultra channels are all correctly in balance with each other? This is important as the Lead and Ultra channels share some features in the circuitry so, if it is only the Lead at fault, then these features are unlikely to be the problem. The opposite holds of course.

You bet, only the lead channel. Ultra and all the rest are fine.

That makes it a little more odd - and more awkward to diagnose.  There is always a fair bit of switching going on inside the H&K amps of this class.  Each channel selection uses miniature relays (nowadays) or solid state switches (in your case) to change component values and configurations in a good number of places in the circuitry.  Yours is a more complex arrangement of that than in the later TM/GM types with more to go wrong unfortunately.  There are switching lines to make changes separately for selections and changes of INPUT-GAIN, LEAD&ULTRA, LEAD&ULTRA-BOOST, CRUNCH-BOOST, ULTRA, CLEAN-OFF, CRUNCH&LEAD, and FX-ON.  Each of those has a separate signal line and multiple switching points in the circuit.

I'm looking into the schematic now so I'll have to get back to you on what suggestions I can come up with.  In the meantime, what experience do you have with electronics repair and in working inside High Voltage units like your amp?  Be honest here, this stuff KILLS!!!

Let's rule out the control section as a probable area of the error. When you have no footswitches inserted and you select the channels manually via the front panel switch do the LEDs all work as they should to indicate your selection? Especially the Lead channel. If they do it means the selector switch is sending the correct data code for each channel and the data lines are being given out the correct command data for switching.

I am fine with the basics,continuity etc. I have a fluke multi meter. The light goes on just like the rest. I bought it used. I was wondering if there is any kind of factory reset. I am new to the "NEW" way amps are designed and built.I do have a foot controller I have not used yet.Thanks for the help.

Good suggestion. The factory reset for the Switchblade is as follows:

Switch off the amp.
Press and hold "STORE" and "FX SERIAL" together.
Switch on the amp.

This should wipe all of the stored Presets and all MIDI settings will be reset to default. MAKE SURE YOU HAVE NO PRESETS YOU WISH TO KEEP IF YOU DO THIS! YOU CANNOT GET THEM BACK AFTERWARDS. I'm not sure this can help with our problem but it shouldn't hurt.

Thanks I am on it, will let you know.Thank you for your input. I am also familiar with discharging capacitors.

I have done the reset and it is still the same.

Oh well, at least it can be definitely ticked off as not a cause now.

As you say the LED for Lead channel select is working we can assume that the microprocessor is responding to the selection and putting out its response onto the control line for that LED.  That would suggest that it is probably sending the other control line responses too.

There are a host of control lines for this area, the Switchblade is much more complex than even the GM series.  The control lines generally respond to either of a pair of the channels.  I think I pointed out that there are 6 miniature encapsulated relays each with three individual switches altering circuit configuration.  (Strictly speaking these are solid state switches not true relays but they act in exactly the same way for our purposes.)  There are lines controlling relays to respond to selections of:  Lead&Ultra, Lead&UltraBoost, Crunch&Lead.  These seem to be the only ones involving a simple selection of Lead.  If any of those chips are faulty then it should show in the other linked channel too.  Bear in mind that can mean a single one of their three switches not acting correctly, not necessarily their overall switching action for all three.  For example, if the first relay in the list were faulty in some way it should show a difference in the Ultra channel as well as the Lead.

Now it may be possible that an equivalent difference in the already high gain Ultra channel, or the Crunch with its lower gain, is not so noticeable.  Is there any possibility that the other channels are different in any way alongside the Lead and you just haven't noticed as it may be less significant overall?

As you can tell I'm struggling to find a cause of just the Lead channel alone having a fault.  We are reaching the point where it would mean digging internally with the amp switched on.  If that is outside of your experience I would strongly suggest you try to find a tech who is prepared to look into it for you.  We aren't talking about desoldering components yet, we're just looking to do tests like tap and push on components in turn with a chopstick.  Even so there are still LETHAL VOLTAGES IN THERE!!!  As Dante said, "ABANDON HOPE ALL YE WHO ENTER HERE!"

Thought I would add something here. With the amp out of its case I am sure the PCBs are upside down in the chassis. This means that you only have access to the underside tracks and not the components. The PCBs are double sided so they are not easy to follow. The Switchblade Service Manuals are out there on the internet and I now have the 50W Combo version, I have seen the 100W Head version too.

That helps a lot though usually they have the same preamp circuitry and that is what we are interested here. I can't post details of the H&K circuit schematics here on the open forum, that isn't fair on H&K. We have a policy of respecting their intellectual property, they make their money from those circuits after all. However, this is an old amp so it isn't really a huge loss to them. Just search for the service manual and you should find it. It will have all of the User Manual, the unit build, the schematics, and drawings of the PCBs and component layouts. If you can find it it may help you to get what I am talking about. I warn you, it's complicated! The microprocessing alone multiplies the complexity by about 3 or 4 times. This is what puts "old school" guitarists off amps like the H&Ks, they can't cope with the idea that things can be modernised and complicated but also more reliable because of it. I'm afraid you are just the unlucky minority in your situation, and the amp is a bit long in the tooth but is still soldiering on.

If it helps have a dig for that manual, it isn't hard to find. Just don't post it here!

Eeeeeaawwww!  (That's a donkey braying.)

I've just come across something else that I was unaware of.  The power amp is also slightly modded for each channel and it does this via 3 classic magnetic relays controlling the signal around the preamp buffer valves and the power amp valves. These seem to be Panasonic types TQ2-24V-1 so are pretty easily available.  2 of these are on their own control lines.  REL-LEAD&ULTRA, REL-CRUNCH.

Testing them in place would be pretty simple if you are experienced.  The coil can be tested for continuity (pins 1+10, 2,880Ω, 2.88k) with the amp off keeping in mind there is a diode across them which means getting the meter leads the correct way around or the diode will indicate a much lower resistance.  If you get a low resistance one way then just reverse the leads.  You should expect to get somewhere around 2.5k to 3.3k.

The switch wafer terminals can be checked the same way with the amp off (and discharged!) but only the NC Normally Connected terminals will work, (pins 2+3, 8+9).  The NO Normally Open ones could only be checked with the amp on when the relevant channels are selected, and as Hamlet said, "there's the rub"!  The amp is powered up and you are right next to the output valves!!! Having a scope to check out signals on those pins is the better option and the right way to do it.

I would think those relays are a prime component to consider as potentially faulty after a long life.  They are mechanical switching components and as such will wear in a way that solid state components will not.  This would be my starting point if I were fixing this.  The downside of that is that these relays are on the power amp PCB NEXT TO THE OUTPUT VALVES AND THE HT!

Hey thanks for the intel, It may be a while before I get back. I have a lot to cogitate hear.