Echobase Voltage regulator issue.

[newfish]

Hi All,

Having built an Echobase from Taylor's excellent PCB, I have a distinct lack of voltage.

I have made no modifications or substitutions from the stock parts list.

Powering up through a small amp gives a 'marching ants' sound - which does not vary in speed or volume no matter which pots are turned.

Measuring voltages reveals the lack of voltage anywhere - on any IC - indicating a short somewhere.

A thorough visual inspection does not reveal any solder bridges.  Taking a break and re-inspecting did not show any bridges either.

Measuring the pins of the 7805 (which is the correct way round), Pin 3 shows no volts, where 5v would be expected.  Pin 1 shows a constant rise and fall from 0v to 2.8v instead of the expected 9v. This will be the marching ants sound, I'm thinking.
I have replaced the Voltage Regulator, as I suspected I'd over-heated it.  This has made no difference.

I have checked the polarity of all electrolytic caps (all are correct), and the 1N4001 diode (also correct).

As expected, an Audio Probe trace ends at Pin 2 of U3 (TL072), since the Op-Amp has no supply to work from.

The supply itself is a healthy 9.2v before connecting to the Echobase - at which point it drops to 0.2v.

Any ideas as to what I should be checking next would be gratefully appreciated.

[Hides-His-Eyes]

Sounds very much like a short to ground from the power supply. Are you sure that no shorting of the 9V is taking place due to an uninsulated DC jack, joint touching the case, or anything like that?

[newfish]

EBase is still in the 'Spaghetti' phase.

I try to make sure things work before casing-up.  It's easier to de-bug.

Project is currently sat on a thick cardboard sheet - with wires carefully spread.

However, I'll be checking my off-boards this evening.   

[newfish]

Shorting issue resolved - ironically, the 1N4001 reverse polarity diode had gone open, and was causing the short.

I now have LED 'on' and 'off' to indicate status, but no sound passes.

Voltages, if anyone would be kind enough to offer an opinion, are as follows...
(I've used a 1N4... diode in-line with the supply as reverse polarity protection - hence the 6v instead on 9v).

U1 (TL072)        U3 (TL072)         U2 (PT2399)       U4 (4066)
Pin    Voltage     Pin     Voltage     Pin   Voltage       Pin   Voltage
1       4.99         1       4.97          1     4.97            1      2.82
2       4.92         2       4.97          2     2.35            2      2.82
3       4.97         3       2.4            3     0                3      0 
4       0.69         4       0               4     0                4     0
5       3.27         5       4.95          5     2.93            5     0
6       4.97         6       4.97          6    2.37             6     0.67
7       4.97         7       4.97          7    3.1 to 3.14    7     0
8       6.25         8       7.0            8    3.08 to 3.15  8    2.39
                                                 9    2.38             9    2.38
                                                10   2.38             10  2.83
                                                11   2.38             11  2.83
                                                12   2.36             12  5.69
                                                13   2.35             13  6.55
                                                14   2.45             14  6.95
                                                15   2.38
                                                16   2.38

                                                Pins 7 and 8 oscillate between the two values shown.

L805
Pin    Voltage
1       6.9 (dropped from 9v by in-line diode)
2       0
3       4.97

2N5089                BC560
Pin    Voltage        Pin     Voltage
E       0                E        0
B       0                B        0.12
C      6.55            C        0.66

Clearly, the TL072s look 'flooded' - so there's no signal getting through.

I'll be re-flowing all joints later today, but in the meantime, if anyone has any advice, I'd be very grateful of your time.

Cheers.

[Taylor]

(I've used a 1N4... diode in-line with the supply as reverse polarity protection - hence the 6v instead on 9v).

It's  quite late here and I'm already asleep... but an inline diode shouldn't drop that much - it should be more like .7v drop. So that's the first thing I'd look into - the circuit won't work as expected with only 6v on all the power pins. You might pull all the chips (you've socketed them?) and measure the voltage with the chips removed. I'd also get rid of your inline diode for the moment - you can replace it once the power issue is worked out if you decide it's necessary.

[deepMago!]

I had experienced same voltage problem with my EchoBase. Voltage dropped around 6V. Changed the power supply the problem was solved. Could be the same trouble for you?
If i remember well my power supply was similar to Medusa from topopiccione site. In that scheme there is before 7809 an hi-pass filter (100ohm and 10mF). Cause the current neccesary to power the PT2399 the voltage after the hi-pass filter dropped to 8V and after 7809 to 6V. On the other lines voltage before 7809 was 14V.
Shorted the 100ohm solved my problem.
Sorry for my bad english...

[newfish]

Thanks for the tip DeepMago!  Your english is very good.
I've tried powering the EBase with a known-good 9v regulated supply, and also tried with a fresh 9v battery.