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Bottlehead Kits => Kaiju Stereo 300B amp => Topic started by: Urbansandz on December 31, 2022, 10:10:35 AM

Title: Driver Testing error (RESOLVED)
Post by: Urbansandz on December 31, 2022, 10:10:35 AM
I made the mistake of using alligator clips testing the IA and OA on the A socket board. These two spots are small and close by and I think what happened is that I accidentally bridged the two resulting in some damage to the board components (see pic). The light is not good, but the R1, D1, and D2 were obliterated. The A side Q1, R2, Q2, and potentiometer appear to have some discoloration, but I'm not sure if usable. Any thoughts on where I should go from here? Get new board/parts? only replace the clearly damaged parts?

Title: Re: Driver Testing error.
Post by: Doc B. on December 31, 2022, 10:22:22 AM
If you look at the schematic you can see that R1 D1 and D2 are in series with Q1, Q2. Sometimes with this kind of damage it will turn out that one or more elements of the zener diode string are blown too. Those should all be checked. Resistance across them should be near infinite in one direction and above 500 ohms or so in the other. If any zener or any pair of transistor legs reads low like 50 ohms or less it is toast.
Title: Re: Driver Testing error.
Post by: Urbansandz on January 01, 2023, 06:29:30 AM
Thank you for the advice.
Title: Re: Driver Testing error.
Post by: Urbansandz on January 13, 2023, 05:26:24 AM
An the A side I replaced the R1, Q1, Q2, D1, D2, and R2 (tested fine, but replaced anyway), . On testing I got 523VDC on IA, but wasn't getting anything on OA. After a short time ~30 seconds R1 burned out, resulting in fried D1 and D2. The burnout happened while I did not have my testing lead on the board. My guess right now is that my initial driver testing mishap burned the board resulting in current flowing from OA to IA, but I'm not sure that makes sense. Otherwise I can't make sense of why R1 would burn out when the IA is testing correctly. Anyway, my plan is to request a new board and new board parts and start over on this board.
Title: Re: Driver Testing error.
Post by: Paul Birkeland on January 13, 2023, 05:40:49 AM
Did you replace the zener diodes that Doc B recommended? 
Title: Re: Driver Testing error.
Post by: Urbansandz on January 13, 2023, 09:51:19 AM
Focusing on the board components I neglected to pay proper heed to DOC's advice re: the zeners, which I've checked and confirmed that they're all toast on the A side (0 reading going either direction), which would explain the issue with R1.  The D side zeners are all ~826 one way and infinite on the other. Thanks for your help. I completed the Moreplay and never had to troubleshoot, so this has been a good learning experience for a me.
Title: Re: Driver Testing error.
Post by: Paul Birkeland on January 13, 2023, 11:19:03 AM
A question that will linger for a bit is how the zener diodes were destroyed.  Were they all properly oriented?  It's possible to mix up the wires going into IA and OA and put the whole power supply across the zener stack, which would blow them right up, but even that is a bit inconsistent with what's gone on here...
Title: Re: Driver Testing error.
Post by: Doc B. on January 15, 2023, 10:19:39 AM
If I am understanding this correctly (50/50 chance) I think that is what the OP posted - that IA and OA were accidentally shorted. So the Zeners got zapped. When we were developing the Paramount circuit I recall doing that a few times myself. The LEDs blow in a most spectacular fashion.
Title: Re: Driver Testing error.
Post by: Urbansandz on January 20, 2023, 09:46:09 PM
I rebuilt the board on the A side and it's working well (516 IA, 296 OA), but then I encountered the same blow-up on the D side, so I'm thinking it wasn't due to bridging OA and IA. Anyway, I rebuilt the D side board and now my IA is looking good at 515, but the OA on the D side board is measuring ~146VDC, so not quite half of what I should be getting. Any thoughts on what could cause such a low DC voltage on OA on the D board?

One more note. If I measure the D board OA right when I power up, the OA is higher, maybe 250VDC or even higher and it seems to slowly bleed down to 145VDC, where it remains stable.
Title: Re: Driver Testing error.
Post by: Paul Birkeland on January 21, 2023, 04:43:11 AM
Check the orientation of the zener diodes in the string. 
Title: Re: Driver Testing error.
Post by: Urbansandz on January 21, 2023, 06:31:53 AM
I attached a photo. The zenners appear to be aligned correctly and they're measuring fine.
Title: Re: Driver Testing error.
Post by: Paul Birkeland on January 21, 2023, 06:34:07 AM
Can you post some photos of the top and bottom of the new board?
Title: Re: Driver Testing error.
Post by: Urbansandz on January 22, 2023, 07:41:24 PM
I've attached photos of the bottom and top of the D side board. I kept the standoff attached because I neglected to provide sufficient working room under the capacitor, so just easier to keep it on.

A few notes regarding the D side board:

1. the LED's on the B side are not lit.
2. R2 on the B side is measuring 69VDC on one leg and 140VDC on the other. A board is ~145/293.
3. R4 on the B side is measuring 69/002 VDC, A board is 142/002
4. bB is 69, but on the A board it's 147.



Title: Re: Driver Testing error.
Post by: Paul Birkeland on January 23, 2023, 05:24:26 AM
If you run the amp with no 5670 on that side, what is your OA voltage under those conditions? (you can just touch your meter probe to the metal tab on the MJE5731A to grab that voltage)
Title: Re: Driver Testing error.
Post by: Urbansandz on January 31, 2023, 04:32:47 PM
When I remove the 5670 on the problem (D side) I get 349 VDC on the OA.
Title: Re: Driver Testing error.
Post by: Paul Birkeland on February 01, 2023, 05:44:37 AM
OK, so that tells us that the zener string is installed and working properly, and that the A side of the C4S appears to be working properly. 

Some things I would check are:

1.  Does this happen with all 5670s?
2.  Are the red wires leaving OA and OB going to the correct places?
3.  What is the Kreg voltage on the B side of the board with the issue?

-PB

Title: Re: Driver Testing error.
Post by: Urbansandz on February 01, 2023, 09:41:52 AM
Thank you Paul.

1. Yes, issue persists after switching tubes.
2. OA goes to +reg B, and OB goes to 46U
3. B Kreg = 1.8 VDC. On the A side board it's 7.36, so that must be where the problem lies, though I don't know how to remedy. Replace the TL431 on the B side?
Title: Re: Driver Testing error.
Post by: Paul Birkeland on February 01, 2023, 10:17:12 AM
Yes, I would put a new 431 in on that side.
Title: Re: Driver Testing error.
Post by: Urbansandz on February 01, 2023, 03:52:50 PM
I replaced the 431 on the B side, but no luck. I'm still getting ~145 VDC on OA and 1.8 VDC on Kreg(B).
Title: Re: Driver Testing error.
Post by: Paul Birkeland on February 01, 2023, 04:23:16 PM
What's the DC voltage at the random pad marked with the "X" on the B side?
Title: Re: Driver Testing error.
Post by: Urbansandz on February 01, 2023, 05:19:22 PM
The x on the B side is measuring 2.65 VDC.
Title: Re: Driver Testing error.
Post by: Paul Birkeland on February 01, 2023, 06:03:55 PM
How about bB?
Title: Re: Driver Testing error.
Post by: Urbansandz on February 01, 2023, 06:56:34 PM
OK, yeah, there's a problem there. I'm getting ~72 VDC at bB.
Title: Re: Driver Testing error.
Post by: Paul Birkeland on February 02, 2023, 04:19:06 AM
Can you verify that the R1 resistor values are in the correct spots?
Title: Re: Driver Testing error.
Post by: Urbansandz on February 02, 2023, 05:30:30 AM
R1(B) is measuring at 215 Ohms.
Title: Re: Driver Testing error.
Post by: Paul Birkeland on February 02, 2023, 05:44:12 AM
At this point it would be super helpful to trade the PC boards between sides.  If the OA voltage stays on the same socket, then we need to figure out what's going on with the socket wiring itself.  If the OA voltage moves with the board, then there's something wrong with the PC board population/jumpering that just hasn't been noticed yet.
Title: Re: Driver Testing error.
Post by: Urbansandz on February 02, 2023, 07:19:10 PM
I switched the boards and the issue remained with the board. The OA was still 145 VDC on the board that was previously on the D side and now moved to the A side. I've attached photos of the two boards. The problem board is on the left in both photos.
Title: Re: Driver Testing error.
Post by: debk on February 03, 2023, 01:44:44 AM
Hard to tell from picture, but the black wire going from bA to -reg has a long bare area at bA.  Could this be touching one of the pads on the pot especially when the wires are compressed when attaching the board?

It's a long shot


Debra
Title: Re: Driver Testing error.
Post by: Paul Birkeland on February 03, 2023, 04:18:09 AM
I would set your meter to continuity beep and be sure none of the legs of Q1 on the A side of the funky board are touching.  It's possible you may have a teeny tiny solder bridge causing problems there.
Title: Re: Driver Testing error.
Post by: Doc B. on February 03, 2023, 08:01:26 AM
Underside pic - right hand board - looks like a cold joint on a 431 pad. The row of pads above IB, fifth pad in from right.

Topside pic - left hand board - possibly a cold/missed connection at the bA pads next to the blue trimpot. Though it seems to look OK on the underside. I'd reheat just to be sure.
Title: Re: Driver Testing error.
Post by: Paul Birkeland on February 03, 2023, 08:46:55 AM
The square solder pad for D2 on the A side on the bottom of the board also appears to be missing. 
Title: Re: Driver Testing error.
Post by: Urbansandz on February 06, 2023, 07:51:27 PM
Thank you all for the suggestions. I replaced the black wire from ba to -reg, repositioned and resoldered the red wire from +reg to IB, replaced the B side R1, and fluxed and resoldered several of the very close soldering points to ensure they weren't touching. I was having some difficulty measuring the B side 431, so I also replaced that again. Paul, you're right about the square pad for the D2 (good eye), I lost it when desoldering an earlier blow out of 90R9F that resulted in blown diodes. The diode seemed to operate OK, so I moved on, but maybe that explains my issues.

Anyway, after all that I turned on the power and still got the ~145 VDC on OA. I left the system on for a bit to perform some testing and then, while not probing the board or components, the 90R9F blew out again. At this point I'm thinking I'll start afresh with a new board and components because simply replacing that 90R9f and affected components might just put me back to square one in trying to locate the ~145 VDC on OA issue. Also, there's enough damage to the board at this point that starting anew is probably the way to go.

Title: Re: Driver Testing error.
Post by: Paul Birkeland on February 07, 2023, 04:09:40 AM
I would definitely put the flux away too.  Rosin core solder already has flux in it, so there's no need for more.
Title: Re: Driver Testing error.
Post by: Urbansandz on February 14, 2023, 02:34:37 PM
Thank you all for your help. My Kaiju is now up and running and sounding great.

I received the new board and components, built up the new board, installed it, and I was initially getting low readings on OA at about ~13 VDC, so I replaced the zener chain and after that the numbers were looking perfect. I put last touches on it today and placed it into my system and it's sounding great.