threshold s200

[neodyne]

Hello, I have a "threshold s200" which had a power transistor HS "MJ15022"
I have completed the replacement by a "mj15022G"
The amplifier works again but I would set the bias, because the repaired heater side a bit compared to the other.
If anyone knows the procedure?
thank you in advance

 

[Zen Mod]

search here , plenty of that
also , see here : Nelson Pass related | Zen Mod Blog

 

[neodyne]

I have not found anything on this blog, do you have a link?
thank you

 

[Zen Mod]

.

 

[neodyne]

ok thank you, but the s200 model must be inserted on the meter but the positive or? the board on the pdf file is not the same as on the s200.

An externally hosted image should be here but it was not working when we last tested it.

 

[Zen Mod]

picture too small in resolution , can't see anything to say something useful

do you know which trimpot is for setting Iq , in your amplifier ?

 

[neodyne]

I'll make you hd pictures and I posts tomorrow

 

[Zen Mod]

........

do you know which trimpot is for setting Iq , in your amplifier ?

 

[neodyne]

The trimpot is a 2k there is one by side

 

[Zen Mod]

then you just set by temperature - to 50C

check exact procedure in file I sent , it's easy - if you are patient

compare currents in two channels - voltage drop at emitter resistors of output transistors

 

[neodyne]

Hello, here are the photos.
Can you tell me where I have to make the measurement with the multimeter?
I replaced the trimpot with a better (SLAB) and especially more accessible for adjustment !!

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.

regards
gilles

 

[Zen Mod]

put voltmeter across one of those 1R resistors - that will give you Iq per transistor

compare two channel values

where is lower - take procedure (smidge by smidge tweak of trimpot) from pdf file , until you get approx. same Iq on both channels , and max. 50C at heatsink

 

[neodyne]

Ok on pdf it recommend 180mv I have to do the measurement between the resistance of 1ohms is that right?

 

[Zen Mod]

well , you being Frenchy , moi being Serb ...... writing on Engrish ...... there surely must be some hiccup

you have non-repaired side , with proper temperature on heatsink;
measure voltage across one emiter resistor (big 1R thingie , any of them) and take that as reference ;

move voltmeter on other side emiter resistor (cold channel) , and re-bias it , to have approx. same voltage across resitor and similar temp on heatsink ..... as other (untouched) channel

if both are well under desired heatsink temperature , re-bias them both

 

[neodyne]

Ok I do the tests I would tell you if it works!
thank you very much !!

 

[neodyne]

Hello, I made the adjustments !! Great!!
I get 180mv with 45 ° for the repaired side.
For the original side I have 320mv for 22 °
I think perhaps we should replace the trimpot? And make the adjustment.
Should all 1ohms 5w resistors be replaced?
regards
gilles

 

[Zen Mod]

something's wrong - 180mV across 1 Ohm , for 45C

and 320mV for 22C

be sure that you're checking same positioned resistors , pcbs are the same .......

recheck other 1R resistors , that way you'll also know is some output transistor gone Dodo

if these resistors are looking good ( no cracks ) and measure good (resistance) , there is no need to change them

 

[neodyne]

Ok but the good value recommended on the pdf is well 180mv for 50 °?