Repairing My Penultimate Zen V4

[Rixsta]

Hello

Last Year I built myself this lovely sounding amp, pics can be seen here
Rixsta

I had it running for about a year, then when i blew one channel up and was too lazy to fix it untill last night. It was the input i thought that caused it to blow as i have no voliume control so if the amp is on and i plug things in it can be sensitive to the buzz or static at the input,which is what seemed to have done it . am i right in saying that if i put in a Volume coltrol and have the amp turned down wheni plug things in i will no longer have this problem of blowing the thing up ? lol

Here is the schematic
http://www.passdiy.com/pdf/zen-v4.pdf
Well anyway to my surprise i open it up and ill tell you which parts have gone
Z1 - Z5 totaly blown and possibly D1 not sure yet
R7 burnt out compleately
R0 slight burn marks
and one of the mosfets was blown i think Q5 the others were ok but i replaced them so far anyway.

So anyway im just about to replace the Zeener stack which i didnt do last night and fire her up again.

When i fire her up i just charge the power supply then connect it to the amp powering from the charge in the capacitors, it's a good way of testing and if all is good you get sound for about 10 seconds untill the capacitors have discharged.

brb
Im no electrician btw lol

[Rixsta]

Ok, replaced the parts, fired her up just from the charge in capacitors, working channel still ok and the channel im fixing, well powers getting thru all the board but as the music fades away on the working channel the music slowly comes in on the broken channel lol of corse it's distorted becuase im running of capacitors for testing purpose.

is it possible a capacitor needs replacing ? i might just replace Q4 now altho it seems ok

If i had the gut's id just wack the power right in but i dont have a variac to slowly bring it up, so dont want to risk it going up in smoke again.

[Magura]

Try a bulb tester.

Magura

[Rixsta]

Thankyou, ill have to rig that up, always meant to lol
basicly it's taking ages for power to get thru the circuit ? i hear the music come thru about 10 seconds after power up and i know thats not right !

am very confused now lol

[Rixsta]

Ok The 4V thats meant to be on Q2 is like 0.5 and ive replaced R7

all transistors but Q4 have been replaced, im realy thinking a capacitor is at fault now
any help apreciated, Time for a break i think lol

[Allen Newby]

Might be worth looking at this thread!
Fail Safe Power Supply

[Rixsta]

Cheers, ive got something setup now
am feeling happy with my troubleshooting stuff
am now at the point where everything works, however

The only reading thats right is the 46Volt after that point it's pretty much half voltage on the whole circuit hmmm

[Rixsta]

Ok am realy actualy stuck now lol

I am about to look one more time to see if i missed anything daft, ive check near enoth every component on the board, it works but is just not as loud as it's meant to be because half of the circuit is running on too low power, but i cant figure out how or why thats happening.

[Rixsta]

Novice electrician almost sorts it out lol Ok dont laugh
i didnt have it biased right, so i learn something new (bias efects almost whole circuit!)
now it looks like only problem is theres no .66 Voltage drop over R0

it's about .002

the investigation continues think im nearly there, hopefully

[Rixsta]

Im Judging by the amount of reply's i must have done something dumb!
it's just realy odd i now have 0V over the bias resistors, yet i still hear sound.
how can this be that all voltages check right apart from the 0.66 ?