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Bottlehead Kits => Crack => Topic started by: illusineer on September 11, 2020, 04:35:57 PM

Title: Wrong voltage on speedball big board [resolved]
Post by: illusineer on September 11, 2020, 04:35:57 PM
OA - 110V
OB - 102V
G - 13V
B+ - 206V

One of my voltages ain't right  :-\ it also reads 13v on the small board test for B-A/B. I plugged in my headphones and only got sound from the right. My amp was working fine before I put the pcbs on it. Also when I was soldering wires on the terminals for the big board sparks popped near the capacitors while I was affixing the wire ends with my pliers (this was after cutting out the 10k 3ws and before putting the big board on). The amp was unplugged but didn't blow the fuse, idk if that has anything to with it or I shorted out the capacitors somewhere while they still had charge.
Title: Re: Wrong voltage on speedball big board
Post by: Paul Birkeland on September 11, 2020, 04:39:20 PM
Please don't plug headphones into an amp that isn't working, as you may end up with headphones that also don't work.

13V on G means you have 13V on terminal 3 as well.  One of the black wires in your amp isn't well connected and is causing this problem.  This is not a Speedball issue.  I would reflow every solder joint in the amp where a black wire connects, then recheck G on the big board.

On the other hand, if your meter says 13mV, that's 0.013V and is plenty close to 0V to be ignored.
Title: Re: Wrong voltage on speedball big board
Post by: illusineer on September 11, 2020, 06:44:11 PM
I tested again, and what I noticed is that my multimeter reads 13-17v just with the black lead on 12u, not touched to the big board's G ??
Title: Re: Wrong voltage on speedball big board
Post by: Paul Birkeland on September 11, 2020, 06:48:16 PM
Can you post the model number or a photo of your meter?
Title: Re: Wrong voltage on speedball big board
Post by: illusineer on September 11, 2020, 06:52:48 PM
It's a klein mm400, read out all the voltages for when I built the regular crack just fine, got it only a couple days ago brand new
Title: Re: Wrong voltage on speedball big board
Post by: Paul Birkeland on September 12, 2020, 05:52:29 AM
The meter may need you to hit the Range button until it goes to auto or down to a low range where you can resolve something close to 0V.
Title: Re: Wrong voltage on speedball big board
Post by: illusineer on September 12, 2020, 08:30:43 AM
That is what I've been doing, I set the meter to volts then press range 4 times until it says 0V. Then I set it to MAX to get a reading that doesn't fluctuate all over the place when I touch the leads. Got my readings this exact way when I built without speedball. Without MAX it just reads 0-1V with 12u and G.
Title: Re: Wrong voltage on speedball big board
Post by: illusineer on September 12, 2020, 10:22:07 AM
12U didn't read 13-17V on my meters max mode on the regular crack voltage tests or any of the terminals that need voltage at 0 beforehand either if my memory serves me right.
Title: Re: Wrong voltage on speedball big board
Post by: Paul Birkeland on September 12, 2020, 11:55:50 AM
That is what I've been doing, I set the meter to volts then press range 4 times until it says 0V. Then I set it to MAX to get a reading that doesn't fluctuate all over the place when I touch the leads. Got my readings this exact way when I built without speedball. Without MAX it just reads 0-1V with 12u and G.

Is there a range that says "auto"? You should be able to measure 1.5V on a AA, AAA, C, or D battery as a test.
Title: Re: Wrong voltage on speedball big board
Post by: illusineer on September 12, 2020, 12:38:36 PM
Yes, I tried a brand new double a battery on auto and it reads 0.000V, I'm starting to suspect my meter is a $50 piece of brand new junk.
Title: Re: Wrong voltage on speedball big board
Post by: Paul Birkeland on September 12, 2020, 12:48:00 PM
If there's a Harbor Freight nearby, the cheap $7 meter they have there is more or less adequate for this kind of work, and the $23 meter is reasonably nice.
Title: Re: Wrong voltage on speedball big board
Post by: Deke609 on September 12, 2020, 12:52:54 PM
Was the meter set to DC volts - parallel flat solid and flat dashed lines?  I have a bunch of cheap meters that I use for doing lots of simultaneous measurements and they require a lot of button pushes to configure properly. 

Don't use the "MAX" setting - it looks for and displays the maximum value measured.  Great for detecting one-off voltage spikes, but not so good for basic voltage tests (and don;t use "MIN" either, for a similar reason). You mentioned that if not set to "MAX" the meter reads 0 to 1V at 12 - and 0 is what you're look for.

And make sure the meter has fresh batteries. I've gotten some crazy readings when using batteries that were only marginally low.

cheers, Derek
Title: Re: Wrong voltage on speedball big board
Post by: illusineer on September 12, 2020, 01:11:07 PM
OK idk if you believe me but I figured out the correct voltage mode before you posted lol. I also redid solder joints on some of the black leads. Here are my readings

OA - 110
OB - 112
G - 0
B+ - 204-210

Everything seemed OK, plugged in my phones and worked for about 30 seconds, then started getting distortion in left channel even with nothing playing.  Not sure if it's related to my problem, but I did see voltage spikes on G a couple times while measuring it with my meter.
Title: Re: Wrong voltage on speedball big board
Post by: Paul Birkeland on September 12, 2020, 01:12:00 PM
Distortion is usually a loose wire.
Title: Re: Wrong voltage on speedball big board
Post by: illusineer on September 12, 2020, 01:16:39 PM
Left channel now doesn't have any sound :/
Title: Re: Wrong voltage on speedball big board
Post by: Paul Birkeland on September 12, 2020, 01:18:35 PM
No sound could be a loose wire/bad connection, or something else.  Have any voltages changed?
Title: Re: Wrong voltage on speedball big board
Post by: illusineer on September 12, 2020, 01:28:01 PM
Voltages haven't changed, any connections in particular I should be looking at? Maybe one of the terminals is changing voltage only when I'm not checking lol
Title: Re: Wrong voltage on speedball big board
Post by: Paul Birkeland on September 12, 2020, 01:38:51 PM
No sound would have me looking for debris across the RCA jacks shorting them out, loose or broken wires going to or from the volume pot, or loose/broken wires going to and from the headphone jack.  Many of the other problems that would cause a channel to drop would also make very noticeable voltage issues.
Title: Re: Wrong voltage on speedball big board
Post by: illusineer on September 12, 2020, 03:07:58 PM
I resoldered some more joints, checked voltages again. Now OB is getting 196V and B+ is getting 230, others didn't change and these two LEDS stopped lighting up (or maybe they were never lighting up?). Also looked at the RCAs and there doesn't seem to be any continuity between their underside soldered tips and the chassis. The pot seems ok and so does the headphone jack, I can take more pictures if it helps.
Title: Re: Wrong voltage on speedball big board
Post by: Paul Birkeland on September 12, 2020, 03:19:54 PM
One black wire on the heapdhone jack looks like it isn't captured by solder.

Is that OB on the big board or little board?  I would guess the big board by your photos.  I would suggest reflowing all the joints on the big board, giving a lot of extra heat to the center leg of the TIP50C.  I would suggest leaving your soldering iron on that middle lug for at least ten seconds. 
Title: Re: Wrong voltage on speedball big board
Post by: illusineer on September 13, 2020, 08:53:43 AM
I redid all the joints on the big board and reattached it, readings are

OA - 119
OB - 218
G - 0
B+ - 227

and the same two LEDs aren't lighting up :/
Title: Re: Wrong voltage on speedball big board
Post by: Paul Birkeland on September 13, 2020, 09:05:14 AM
There's a broken wire from the board to the socket, or a miswire from the board to the rest of the circuit, or there's still a bad solder joint on the board itself.  The B+ being high and OB being high means that half of the board just isn't allowing half of the 6080 to draw current.
Title: Re: Wrong voltage on speedball big board
Post by: illusineer on September 13, 2020, 12:20:15 PM
I looked at the board and the wiring back to the circuit and I can't see anything obviously wrong. It seemed so close to working now I'm not sure what to do
Title: Re: Wrong voltage on speedball big board
Post by: Paul Birkeland on September 13, 2020, 12:30:25 PM
You have a solder bridge across one of the LEDs on the bottom of the board.
Title: Re: Wrong voltage on speedball big board
Post by: illusineer on September 13, 2020, 12:49:58 PM
Wym where? All I see is the oily looking residue from soldering, is that stuff conductive?
Title: Re: Wrong voltage on speedball big board
Post by: Paul Birkeland on September 13, 2020, 01:05:21 PM
Solder bridge, iffy joint, and leads to be trimmed.
Title: Re: Wrong voltage on speedball big board
Post by: illusineer on September 13, 2020, 01:58:42 PM
How's that? Good to go back into the circuit?
Title: Re: Wrong voltage on speedball big board
Post by: Paul Birkeland on September 13, 2020, 02:15:11 PM
On each leg of each TIP50 transistor, I would hold your soldering iron on there and count to ten, then move on to the next leg.  You can do one leg of the A transistor, then a leg of the B transistor, then back to A, etc. switching off to keep the transistor from heating up too much.

It also looks like maybe one end of one of the 47K resistors needs some more heat and solder.
Title: Re: Wrong voltage on speedball big board
Post by: illusineer on September 13, 2020, 03:19:12 PM
OK, so I did all of that, put the leads on the board again, go to do resistance checks, then OB gives me around 4.6 megaohms, and OA doesn't read anything.
Title: Re: Wrong voltage on speedball big board
Post by: Paul Birkeland on September 13, 2020, 04:08:08 PM
As long as that's not close to 0, then you pass that resistance check.
Title: Re: Wrong voltage on speedball big board
Post by: illusineer on September 13, 2020, 04:35:30 PM
What about OA? It doesn't give any reading while the other one did give a reading on my meter.
Title: Re: Wrong voltage on speedball big board
Post by: Paul Birkeland on September 13, 2020, 04:58:25 PM
One side is reading 4,500,000 ohms and the other side is reading so high your meter can't determine what it is.

The manual says OA and OB on the big board should be several hundred thousand ohms at minimum.

I'm not seeing what the issue is here, I would move on to checking the voltages.
Title: Re: Wrong voltage on speedball big board
Post by: illusineer on September 13, 2020, 05:16:09 PM
OA - 120
OB - 221
G - 0
B+ 246
Title: Re: Wrong voltage on speedball big board
Post by: Paul Birkeland on September 13, 2020, 05:20:21 PM
Let's go back to pictures of the bottom of the board...
Title: Re: Wrong voltage on speedball big board
Post by: illusineer on September 13, 2020, 05:27:19 PM
Trying my best lol, this pcb soldering stuff isn't as easy as the stripping wires and soldering them to terminals sticking up ig...
Title: Re: Wrong voltage on speedball big board
Post by: Paul Birkeland on September 13, 2020, 05:34:01 PM
Can you send me a link to the solder and soldering iron you're using?
Title: Re: Wrong voltage on speedball big board
Post by: illusineer on September 13, 2020, 06:05:01 PM
I've been using this 60/40 rosin core radioshack solder that's been lying around in my garage forever throughout the whole amp, as for irons I've used this bluepoint soldering gun for about 95% of the time except for just recently with the pcbs I started using this weller iron (I like the soldering gun better).
Title: Re: Wrong voltage on speedball big board
Post by: Paul Birkeland on September 13, 2020, 06:05:47 PM
I would use the gun on your board.  You can leave the LED joints alone, but use the gun on everything else. 
Title: Re: Wrong voltage on speedball big board
Post by: illusineer on September 13, 2020, 06:35:47 PM
OK, reflowed with the gun put the board on again, resistance check, meter didn't read anything, voltage check

OA - 117
OB - 220
G - 0
B+ -226

Title: Re: Wrong voltage on speedball big board
Post by: Paul Birkeland on September 13, 2020, 06:37:32 PM
Well, at this point I would suggest sending it in for repair and I can fit a new board on it for you, or you can e-mail replacementparts to ask for a new board, or you can pull the LEDs and the two transistors on the bit that's not conducting and replace them.

Board rework isn't super easy though.

It's moderately probable that the big lump of solder that I saw bridging the connections on one of the LEDs would've required enough heat to melt the LED itself, and it may be damaged.  Some meters have a diode check setting that can allow you to measure them, and they should show about 1.57V in one direction and nothing in the other.
Title: Re: Wrong voltage on speedball big board
Post by: illusineer on September 13, 2020, 06:56:46 PM
My meter does seem to have a diode check, not sure how to work it though. I'm not super eager to spend more $ to send it back for repair tbh especially having been so close to having everything working  :-\
Title: Re: Wrong voltage on speedball big board
Post by: Paul Birkeland on September 13, 2020, 07:10:21 PM
Well, you can get some solder braid and wick the solder out of those joints.  I would start with two new LEDs, then see what the results are before yanking out the transistors.
Title: Re: Wrong voltage on speedball big board
Post by: illusineer on September 20, 2020, 02:33:27 PM
I went ahead and replaced the big board and everything on it with new parts, did the tests and everything works now. Thanks