LowRider voltage issues

[jeffrey.ollar]

I'm hoping to find someone familiar with the LowRider. I'm referring to the post 2015 version. I'm not getting voltage between ground and IC5 pin14 or IC6 pin4. When I measure the resistance between the two I get 33K just as the one resistor between the two should show, and all the surrounding pins on both chips show correct voltages. I've tried swapping out both the IC5 and the IC6.  Is there an unbuffered 4013 that I should be using?

[jeffrey.ollar]

If anyone was wondering, I had Q3 transposed..

[nzCdog]

Ah... Well done,  working ok now?

[FRANKO]

Sorry for resurrecting this old thread, I've completed a Lowrider (2015) and everything seems to work just fine but I'm getting some strange measurements compared to voltage chart.

Power Supply     8.9V (after D11)

IC1

1   4.9
2   4.9
3   4.9
4   8.9
5   4.9
6   4.9
7   4.9
8   4.9
9   4.9
10   4.9
11   0
12   2.4
13   4.9
14   4.9


IC2

1   4.9
2   4.9
3   4.9
4   8.9
5   4.9
6   4.9
7   4.9
8   4.9
9   4.9
10   4.8
11   0
12   4.9
13   4.9
14   4.8


IC3

1   4.9
2   4.9
3   2.9
4   8.9
5   5.7
6   4.9
7   4.9
8   4.9
9   4.9
10   2.9
11   0
12   4.8
13   4.9
14   4.9


IC5

1   4.8
2   4.9
3   4.6
4   8.9
5   4.6
6   4.9
7   5
8   1.2mV
9   4.9
10   4.8
11   0
12   4.9
13   4.8
14   2.6   


IC6

1   4.8
2   4.2
3   0
4   2.3
5   0
6   2.2
7   0
8   0
9   4.5
10   0
11   4.2
12   4.5
13   4.5
14   8.9



IC7

1   4.5 (UNSTABLE BETWEEN 4.3 AND 4.6)
2   4.5 (UNSTABLE BETWEEN 4.3 AND 4.6)
3   4.5
4   0
5   4.5 (UNSTABLE BETWEEN 4.3 AND 4.6)
6   0
7   0
8   0
9   0
10   0
11   0
12    0
13   8.9
14   8.9




IC4

1   4.9
2   4.9
3   4.9
4   0
5   2.9
6   4.9
7   5
8   8.9


Q1
D   8.9
G   2.5
S   8


Q2
D   4.9   
G   1.5
S   4.9


Q3
D   4.8
G   1.5
S   4.9


As I said everything seems to work, all the octaves are being generated, but I'm sure there is something wrong considering how many voltages are completely off.

I've already scraped between the pads, changed ICs and transistors, resoldered here and there, but no changes so far..

[FRANKO]

Bump

I've desoldered and resoldered everything, cleaned up the board once again but no luck.

How can it work and sound good with voltages so off?

[madbean]

Some of those voltages likely have an easy explanation: DMM's can cause an issue when measuring voltages on the inputs of some ICs if there is an internal resistance present between your leads - what happens is the leads themselves act as a voltage divider and end up reducing the measured voltage (iow, the act of measuring affects the voltage). I've had this very thing happen before on one of the multimeters I owned. I would make sure you have used a 1M resistor on R4 and not something like 10M, but I think the former explanation is the likely case.

The gate voltages on the FETs could come down to individual specs on the devices themselves, whether its their VGS ratings or some other spec. The FETs are being used as variable resistors here so as long as your octaves are triggering then I would not be concerned.

IC7 pin13 is a little more concerning. That pin is untied to anything. So there are a few possibilities here: 1) I measured that pin incorrectly and there is some internal resistance between pins 13 and 14 in the actual IC which would cause a reading of VC there 2) there is continuity between those pins either in the traces on your board or via a solder bridge or 3) you have a bad part. What I would do there is unplug the circuit, remove IC7 and if you have a continuity checker, test pins 13 and 14 in the socket to see if there is a connection. If so, check the traces and pads underneath for a board error or solder bridge. In the end, it may not matter if there is because like I said pin13 is not used for anything. As long as your IC is not getting really hot then you are probably fine.

[FRANKO]

Thank you Brian, R4 is 1M and IC7 pin 13 is actually 0V, maybe I've just wrote it wrong.
I'm not sure about the DMM, I'm getting the same measurements from three different units