Akita AT-40 power supply weirdness

[T9c]

I'm trying to fix an AXL Akita AT-40 amp that's got me scratching my head. The unit originally powered up, but hummed badly and was passing tone poorly. I replaced the main filter caps, C70,71 with same brand and capacitance but higher voltage - 220uF 450v.

When I brought the unit back up with the variac, I got a light snap sound like a fuse blowing, but all fuses are fine. I had forgot to secure the output xfmr taps to their respective lugs on the PCB. Once that was resolved, I'm not getting any B+ voltage at all, but instead I have -250vdc at D12,13 thru the STBY switch. All other PT taps are yielding correct Vdc's in thier circuits. Checked all resistors & rectifiers-OK. Replaced D14,15. Even pulled a leg on R82. 100% positive I installed the filters correctly(double checked).

Geez, I know it must be something I'm overlooking, but my feeble brain is in no comprende over this one. Can anyone shed some light for me?

[52 Bill]

Geez, I know it must be something I'm overlooking, but my feeble brain is in no comprende over this one. Can anyone shed some light for me?

The chassis is not directly connected to the power supply ground. Where are you attaching the negative meter lead?

Is there a better schematic out there?

[T9c]

Better schematic

I used TP0 for the neg lead. I'll rescan a larger schematic and repost.

Hopefully, this one's a little easier to read.

[52 Bill]

I used TP0 for the neg lead. I'll rescan a larger schematic and repost.

If TP0 is at the one end of the standby switch, I'd check to see that it is in fact directly connected to the filter cap ground line. Check for burned traces, etc.

[T9c]

If TP0 is at the one end of the standby switch, I'd check to see that it is in fact directly connected to the filter cap ground line. Check for burned traces, etc.

<<SOLVED>>
ACK! Yep, the plated thru holes on one of the filter caps is broken, thereby lifting the cap from circuit ground. Looks like some patch wiring is in order now!
Thanks Bill!

[J M Fahey]

Congratulations.
Your schematic claims to be a PDF (it says so), can't you post the straight PDF here?
Will certainly be more readable.
Or if you only have a paper copy, please scan it in 2 parts, because clearly it's larger than your scanner and is always incomplete.
Thanks.

[T9c]

Congratulations.
Your schematic claims to be a PDF (it says so), can't you post the straight PDF here?
Will certainly be more readable.
Or if you only have a paper copy, please scan it in 2 parts, because clearly it's larger than your scanner and is always incomplete.
Thanks.

Hi Juan, yes it was a pdf, printed out by my customer presumably and given to me all wrinkled. The schematic was originally scanned crooked as well. I did scan it again to pdf for my files, but I don't have the option of posting a pdf here. Only option I can see is to UL bitmaps (images). I googled and found a site that will sell it for 6 euros, though.

[tube dude]

Hi Folks,
I too have had a problem with the Akita. Originally the owner, who is sadly blind, plugged an effects unit into the one of the ext spker jacks..so he said and trouble began.
Akita said there is no way this should cause a problem...........
Finally got a schematic from their supposedly support tech or whoever answered the phone. Their support is dead and can't find the number now. Can't locate any support from them now. Me personally,
wouldn't buy one of these Chinese amps. Same suggestion for the Buddha amps that Peavey is now taking care of.
Seems like a couple of people made a new business of importing these and left it at that. MONEY!
Anyway, I finally, after several blown f1 fuses realized I had plugged in the preamp lead one leg off.
Now it doesn't blow the fuse, comes on and makes an awful hum. I will once again remove the circuit board and check the connections of the main power caps.
Previously I removed and tested all the caps in that area of the board. 8 of them plus the two larger ones. Found one that wasn't up to par. I use an Eico cap tester for the testing of caps.
I will let you all know about my findings on these power cap connections. About the TPO, does it connect to the chassis via a screw through it? Curious!
Later tube dude

[tube dude]

Akita 40

Hi,
Do you still have the schematic(s) for this amp?
I am still working on this thing!
If so would you send me a copy o\f it?
my email is kracked@swbell.net.
Can't find any tech support...personally I will never have another one.
Thanks!
Tube Dude
Oklahoma

The chassis is not directly connected to the power supply ground. Where are you attaching the negative meter lead?

Is there a better schematic out there?

[T9c]

email w/ attachments sent!

Hi,
Do you still have the schematic(s) for this amp?
I am still working on this thing!
If so would you send me a copy o\f it?
my email is kracked@swbell.net.
Can't find any tech support...personally I will never have another one.
Thanks!
Tube Dude
Oklahoma