Hot rod deluxe stuck in drive mod (cannot switch to clean)

[Barakuda]

Hey everybody, i need help
I have a problem with my amp, it stuck on drive channel
(the led is yellow), and more drive working fine and the led turn to red.
I have cheked tp31-36 and found wrong voltages:
tp31 = -0.1v
Tp33 = -13v
Tp2 is ok = 0.5v with switch off, 9.9v switch on
The voltages in u3 chip (drive channel):
Pin1 = -15v
Pin2 = -0.5 (with more drive -9.7v)
Pin3 = -4.75
Pin4 = -16.5v
Pin5 = -0.1v (need to be 1.07v (tp31))
Pin6 = 9.8v (tp32- when drive switch off its 0.5v)
Pin 7 = -13v (tp33 - need to change from -13 to +16v when drive switch is off)
Pin8 = 16.7v

*I have 16v in r91 read, but his other side 0v, why?
*Cheked r91,90,r89,r84,r101 all read good
The amp is without tubes and speaker, and standby switch is off - it works in this state in my second hrd that i have.
Someone have an idea?

[nickb]

What is the voltage at the anode of CR20 ( i.e junction CR20/ R90, R91)?

The should be around 1.3V. If that is correct then check that R90 is not high resistance. If that is OK replace U3.

[Barakuda]

Short diodes

Ok i found cr20, cr27 are shorted
I put them out and test with dmm
Thay are not good.
I will replace them and tell if it works.
Thank you

Can i replace them with 1n4148?
The stock is 1n4448...

[Enzo]

if all you have is 1N4148, try it for test, it will probably work, and won't hurt anything even if it doesn't. But it really ought to be 1N4448.

[Barakuda]

I replaced the two diodes and the problem solve!!!
The channel is switching.
I put 1n4148 but i will replace again when i receive 1n4448.
Thank you all

[gbono]

1N4148 is so close to the 1N4448 I wouldn't bother changing them out.

https://www.fairchildsemi.com/datasheets/1N/1N914.pdf