SX-1010 schematic question / error / issue

[merlynski]

I am helping on an SX-1010 problem with the High Filter lamp being illuminated slightly when the switch is off.
While perusing the very complicated Dim / Bright and High Filter switches' connections I came across an anomaly in the schematic. The common side of the Low Filter, High Filter, AF Muting, Stereo/Mono and Loudness lamps do not connect anywhere except the common side of those lamps. Sorting through the logical functions of the switches makes me think it should be connected to ground.
The circuit portion I am confused about is marked in GREEN. The GOLD path is the switchable Dim/Bright DC supply.



Has anybody noticed this before? Have a resolution?
Got one open on the bench?
I have never had my hands on an SX-1010 so I cannot resolve this from experience, I have only a schematic and SM.
Thanks!

 

[markthefixer]

Ok, you have a point.

It would depend upon how the wire wrapping for those lamps was done.
There has to be two posts for a lamp's wires and while sometimes they double up wires on pins, it's not all that common.

Looking at the schematics and board layouts

The group of 3 lamps (lo cut, hi cut, 20db) & the group of 2 lamps (mono,loudness) are WIDELY separated on the front panel.

AWS-070 mono (on) switch, loudness (on) switch.
When either or both switches are off, the dim/bright supply has 150 ohms load to ground for each unlit lamp, and the lamp itself is isolated.

When either or both lamps are on, that lamp has it's own 47 ohms to the dim/bright supply, and each of the 150 ohms to ground is isolated.

and an unknown common to both lamps



AWS-071 lo filt, hi filt & muting

When any or all lamps are off, the dim/bright supply through 15 ohms has 150 ohms load to ground for each unlit lamp, and the lamp itself is isolated.

When any lamp is lit, it is drawing through the same 15 ohm resistor, connected to the dim/bright supply.
An unlit lamp is isolated.

and an unknown common to all three lamps

Thus with all FIVE lamps, when they are unlit they are isolated.


We need to open up a unit and see where the 3 common and two common lamp leads are wire wrapped to.

Since BOTH boards are fed (AWS-070 pin 2 and AWS-071 pin 1) by the dim/bright supply my vote is for chassis grounds.
Note on the boards that the analog and lamp grounds are two separate entities.

 

[merlynski]

Thanks for your input.
Yes, that is my point. The schematics OFTEN are poor representations of a true wiring list that an Engineer would create and an assembler would use to build the units, especially for ground connections.
For the circuit to work as drawn it would have to violate Kirchhoff's Laws.
Anybody got one open on their bench?

 

[markthefixer]

I pulled one aws-070 and 2 aws-071 boards from parts storage.

They still had short lengths of colored insulation wire wrapped to their pins.

Mapping the pins and colors on the three boards gives a strong probability that those common leads of the lamps are grounded.

Same results were obtained by looking at eBay listing pictures for those boards. Two -071 boards and one -070 board currently.

I have a sx-1010 that's halfway done, but it'll take me 2 days to just dig it off the shelf, no less open it up.