Help reading schematic for Casio synth - Page 1
Forum section: electronics / beginners

author: mathsquid
author_rank: Frequent Contributor
timestamp: July 27, 2016, 01:31:07 pm
content: Hi everyone. I'm having some trouble reading this schematic for a casio keyboard, and I was hoping that someone with more knowledge and experience could look at it and maybe see what I don't. I was hoping to power it from a 9.6v rechargeable battery instead of 4 D batteries. I suspect that the 0.6v overhead would pose no problem, but I wanted to check the schematic to see what sort of regulation happens inside. That's where I got stuck.The whole schematic is at http://www.burnkit2600.com/manuals/CASIO_CZ-1000_SRV.pdf on page 4, but the attachment shows the part that I'm asking about, with parts of it color-coded. I shaded what I believe to be ground in green, and what I believe to be the positive power from the battery/power supply in red. The dashed red looks like it's the positive rail, but I'm not so sure about it. In blue there are three things I don't understand.1. There are two diodes in parallel. I figured that they were there to do some sort of regulation, but if my dotted red is the positive rail, it looks like the two ends are shorted together.2. It looks like there is a short between the positive and negative where I labeled "looks like a short".I'd appreciate it if anyone could help me understand the schematic; I'd also be interested in advice about just whacking in a 9.6v battery.Thanks!

author: MosherIV
author_rank: Super Contributor
timestamp: July 27, 2016, 01:43:34 pm
content: Quote4 D batteries is 6V NOT 9V

author: Andy Watson
author_rank: Super Contributor
timestamp: July 27, 2016, 01:48:33 pm
content: Quote from: mathsquid on July 27, 2016, 01:31:07 pmIt is odd that there are two of them but in the absence of further evidence I would say they are reverse-polarity protection - i.e. if the power-pack or battery is inserted the wrong way the will short it out.QuoteJust part of the drawing - a boundary box where signals leave the PCB and connect to wires.

author: rstofer
author_rank: Super Contributor
timestamp: July 27, 2016, 02:04:00 pm
content: Quote from: MosherIV on July 27, 2016, 01:43:34 pmThe schematic seems to indicate 6 cells, not 4There's no way in the world a 9V battery will be able to provide the amps and amp-hours of D cells.

author: CJay
author_rank: Super Contributor
timestamp: July 27, 2016, 02:07:45 pm
content: Quote from: rstofer on July 27, 2016, 02:04:00 pmIn fairness he doesn't specify what sort of 9V rechargeable and as he specifies 9.6V I'm thinking it's some sort of 'pack' rather than a small PP3/6F22 rechargeable but of course I may be wrong and of course it will need to be of good capacity to beat 6 D Cells...

author: helius
author_rank: Super Contributor
timestamp: July 27, 2016, 02:32:55 pm
content: As has already been mentioned, the box around each circuit board is just a box. The connector pins are usually numbered there.This part of the circuit allows for power from either the batteries or power pack. The (-) side of the power pack is connected to ground, and has an EMI filter with the (+) side. The power jack is normaled so that when the plug is removed, the battery (+) makes contact with the positive rail. The two diodes are just there to avoid arcing when this normal contact closes: as the power plug is removed, the positive rail comes down to .5V below the battery voltage, then the normal contact closes and brings it back up to 9V.As a general matter, dotted or dashed lines usually aren't electrical connections. In a multi-pole switch, the mechanical linkage between the poles is a dashed line.

author: mathsquid
author_rank: Frequent Contributor
timestamp: July 27, 2016, 06:43:08 pm
content: Quote from: helius on July 27, 2016, 02:32:55 pmThanks to you andAndyfor pointing this out--it clears things up quite a bit. I thought something was up with the broken line, but in some places there are no breaks between two connector pins, making it look (to me) like a connection.Quote from: helius on July 27, 2016, 02:32:55 pmThanks for the explanation!

author: mathsquid
author_rank: Frequent Contributor
timestamp: July 27, 2016, 06:51:21 pm
content: Quote from: CJay on July 27, 2016, 02:07:45 pmThat is what I had in mind. I wanted to use an eight-cell 9.6v NiMH battery pack instead of six D cells.

author: dentaku
author_rank: Frequent Contributor
timestamp: July 28, 2016, 09:47:12 pm
content: CZ series Phase Distortion synths look like fun. I'd love to find one at a yardsale or something. Most people just think it's another Casio toy but they definitely aren't.