Melos Sha Gold
 

Hi There!
I got one of these with a fault.
It powers up "normally",but no light in tubes.
This fault has suddenly occured after playing well for a long time.
Anyone got hold of some scematics or knows were to find it?

Regards,
ManUtd

Hi ManUtd,
If the heaters aren't lighting it should not be too difficult to troubleshoot. If you find a blown fuse, check any rectifiers in the heater circuit if they exist first before replacing the fuse. I am not familiar with this amp, just general advice.

-Chris

Hi Chris!
Thanks for Your help,unfortunately heaters are lightening.
I think i do need schematics to figure out more.

Reg,
ManUtd

Hi ManUtd,
Okay, I misunderstood you completely. What exactly is happening (or not)?

-Chris

Well,amplifier turns on and led in front starts blinking(Normal).
Blinking is indicating "warm up" in approx. 3minutes.
But blinking do not stop and i can hardly see that Tubes are on(light).I have measured 90V input to Tubes.
The 4 leds located at 2N6045 are on.
There is 2 transistors on Heatsink with no value on it.(I mean text on them are scraped off).

Regards,
ManUtd

Hi ManUtd,
They may be three terminal regulators. No biggie.

So you are saying it never comes out of warm up? Check the ripple on the heater supply. If it's too large (cap going, going, well kinda gone now) the timer circuit will be constantly reset.

Do you have an oscilloscope and meter available to you?

-Chris

Hi Again,
I had to sleep(fresh up my mind).
Yes I got a scope and Multimeter(Fluke).
Do You know what voltage shall be read on ECC88 pins(I mean typically) i think the 90V measured is normal.
Soon I will have Scematic also,thanks to this forum.


Reg,
ManUtd.

Download Scematics Here:
http://www.eserviceinfo.com/download.php?fileid=21578

Hopefully it works too!

Hi ManUtd,
Thanks for the link. I can't make out the exact component values but now I have a good idea what it "looks" like.

Use your 'scope and look at the plate (set for 50V/div, AC coupling, and reduce to show signal - be nice to the Y amp :) ) Then look at the gate of the 2SK68A followed by the source.

The grid voltage of the 6922 is undefined, but you want to see the cathode more positive. The tail current can be figured out by measuring across the 68 ohm resistor on the source of the 2SK107.

Let me know what you get.

-Chris

Everything seems to happen to me right now.

I tried to start my old Scope from Philips but it is only beeping in it, no signal in screen.
Before that i measured 60mVDC across 68Ohm resistor.
Measured with no signal and after 3minutes warm up.



:(