H&K Triamp MK II neon lights not working

[GainFreak]

Hi,

The only problem with this amp is the neon lights are not working. I measured 0.5V at the plugs (marked #25 and #26 on the PCB) feeding neon lights' switching power supplies. When disconnected the voltage is drifting between 3V and 6V. Before that the owner replaced the lights and supplies with new ones assuming that they burned but obviously that's not the case.
Unfortunately I couldn't find schematic for the MKII. The only one that is available is for MK1 and I wouldn't like to disassemble the whole thing only to find out where these plug traces are going.
I emailed H&K but no answer so far. I would appreciate your help fixing this problem.

[drewl]

Ive seen these type of lights offered by typical places like Mouser, Digikey and MCM.

[GainFreak]

As I already mentioned the lights were replaced with brand new ones by owner and are still not working.
The main PCB is not feeding enough voltage to the switching power supplies.

[Jazz P Bass]

The inverter for the CCFL neon lamps runs on 12Vdc.

So, yeah, it's dig time to find out why you are not getting the proper voltage to the inverter.

[GainFreak]

I tested the lights by feeding them gradually 1.5 to 12 Volts and they light up completely at 12V, so they are OK.
After couple of hours of poking into the amp I guess I figured out where the switching supplies are fed from. It looks like a voltage doubler coming from power tubes heaters. One of the caps was somewhat inflated so I'll change it tomorrow and see how it goes.

[52 Bill]

I tested the lights by feeding them gradually 1.5 to 12 Volts and they light up completely at 12V, so they are OK.

Okay, I'm confused here but that's easy to do. You fed the lamps themselves 12 volts and they light up or you fed the inverter 12 volts and the lamps light up?

[Jazz P Bass]

I take it the OP is calling the inverter a 'switching supply'.
(which it very well may be: for the lamps)

[GainFreak]

Okay, I'm confused here but that's easy to do. You fed the lamps themselves 12 volts and they light up or you fed the inverter 12 volts and the lamps light up?

I'm sorry, I meant I applied 12V to the switching power supplies feeding high voltage to the neon lamps.

[GainFreak]

Problem is now solved. It was one of voltage doubler diodes. Below you see the location of the circuit (components marked with red dots) and what I could trace from above:

[The Doctor]

I realize this is an old thread but I'm hoping to get some answers. I have a Triamp Mk II. One of the bulbs seems to be failing. I'm having the devil of a time finding replacements. Anybody.

Also tips on getting the chassis out.

[Enzo]

Hi Doc, welcome to the forum

It is good form to start a new thread for your amp. Tacking on a five year dead thread won't get a great response often.

I have not been in an H&K in years, though we were a former warranty station. I don't recall them being odd. As with anything, there will be rear covers/grilles that are likely in the way. Then screws through the cab to hold the chassis. Sometimes those are the screws holding the feet.

[The Dude]

Welcome Doc!

I haven't any idea what bulbs are in there, but in post #4 above Jazz says there's an inverter and CCFL bulbs running on a 12V supply. Rather than look for oddball lamps every time, I might think of ditching the lamps/inverter and getting some 12V LED strips of the appropriate length. They're easily had all over the interwebs for different automotive projects.

[The Doctor]

As it turns out the bulb was fine. There was a broken wire so a little solder and all is well.

It came apart nicely. For anyone that happens to run across this thread and wants to know how to get a Triamp MK II apart.

Tube cover: 2 screws on each side.
Bulb guard: 3 screws on the top
All rubber feet on the back
Chassis: four screws from the bottom

That's it. Slides right out.