It may have been Molex KK I was thinking of, and having now seen the picture, that's apparently not the right one.

I don't think I've seen one with long blades, like that. I was thinking of shorter blades, running across the connector - i.e. perpendicular to those.

Maybe you could replace the connector on the board with Molex though... It might not be a very secure fit to the cable, so you might have to replace the cable, and the other connector it went to as well, or at least the connector at that end of the cable.

- Andy

It's pretty unlikely that they are Molex as Yamaha would source locally or
make their own. I also don't recognize the blade configuration. If you
want to find the originals they will likely be from a Japanese
manufacturer.

For connectors with fewer than 10 pins you can sub a different connector
type even if the pin spacing is not exact for 2.5mm vs. 2.54mm pin
spacing. If the connectors are longer then the tolerances add up and this
won't work. You would need to change the wire ends too which is a pain.

A common and easy to use connector series is the Molex KK .1" (2.54mm).
You can get them with a gold or tin plated finish. They are about the the
easiest to crimp and insert. You can get them with keys and ramps which
prevent misalignment and lock the connectors in place

Here is a Digikey link



HTH,

Dave


On Sat, April 6, 2019 7:47 pm, mjkirk12@... [YamahaDX] wrote:

Thanks, I will look at Molex. Hope they are not discontinued. Picture
attached of cable and connector.

daved@...

Thanks, I will look at Molex. ?Hope they are not discontinued. ?

"2.5 mm spacing on the pins - which are not square, but a flat blade type."

Sounds like it's 2.54mm Molex.

- Andy

I need to replace a mainboard connector (J13) on my DX7S.

I didn't even know there were electronics in it? I thought it was just physical shape and maybe dropping a few pins. In any event, if Yamaha are anything like Roland then the schematic or layout is probably in one of the synth service manuals.

I have a DX7S in pieces that I'm am trying to fix, so I may be interested in this too.

A small silcon diode, like 1N4148 would work fine, but a Germanium diode will allow you to squeeze more life out of a 3V battery, by dropping less voltage.?

If the battery is in a clip, it's less important than it was originally, but Germanium diodes are not anything particularly exotic, so get one of those, yes.

FWIW, I've bought 1N34A Germanium diodes on ebay - I got 20 for ?1, though they took a while to arrive, so you'd probably want to shop closer to home.

To check a diode is a germanium one (Ge), use a meter that has a diode test or put it in series with a 1k resistor and use a 9V battery, then measure across it.? In either case, it should show close to 0.3V.

- Andy

Considering the previous post describes in great detail why the 1N4148 is NOT the ideal choice, I would use it only if a germanium is not available. It shouldn't be that hard to find a suitable germanium diode.

A simple 1N4184 does the trick - BTDT ;-)

开云体育

Hmm, it's a bit hard to say, definitely.? It wouldn't be my first, or even second, choice.

A 1N4004 is a silicon power rectifier diode, designed to conduct up to 1A of current; while the OA95 is a germanium small-signal diode, designed to conduct up to 50mA of current.? Since the DX7 only needs a tiny current through the diode to keep the RAM from losing its data, the current rating doesn't matter.

What *does* matter is the forward voltage drop of the diode.? This is voltage lost by the act of conducting current, and is never zero.? The drop varies with the current flowing through the diode, but is generally lower for germanium diodes than their silicon counterparts; and lower for small-signal diodes than their power equivalents.? Looking at the data sheets, an OA95 is likely to drop 0.2-0.3V at the currents required, while the 1N4004 is likely to drop 0.6-0.7V.

What does this mean to you?? In the best of circumstances, it will probably work, but the backup battery is going to read as 'bad' long before the end of its actual life.? A lithium coin-call battery is about 3V when new, and it drops to around 2.3-2.4V when it's pretty well used up.? I don't know the minimum voltage needed by the DX7's RAM chips, but let's assume that it's 2V.? If so, an OA95 can work until the battery is 2V + 0.2-0.3V = 2.2-2.3V; the 1N4004 can only work until the battery is 2V + 0.6-0.7V = 2.6-2.7V.

In the worst of circumstances, some other property of the DX7 circuitry requires a higher voltage than 2V to work properly, perhaps as high as 2.5V.? In this case, even a nearly-new battery may not be able to provide enough voltage to meet or exceed this situation, leading to data corruption.

If an OA95 isn't available, I would recommend (in rough order of preference)

1. Another small-signal germanium diode.
2. A Schottky small-signal diode, such as a BAT81S or BAT83S.
3. A silicon small-signal diode, such as a 1N914 or 1N4148.
4. A higher-power germanium diode.
5. A higher-power silicon diode, such as a 1N4001 or 1N4004.

Of course #1 through #4 are not likely to be found at the local DIY shop; one would have to order them from Mouser, Farnell, Allied, etc., or find one on eBay.

Just my $0.02USD ...

I think it does make sense! Just been a very busy week and I'm hoping to get back in there to work on the DX7 this weekend when I have a bit more time.

I don't know what happened with the attachment.? Yahoo messages can be very mysterious. I'd just googled for images of an OA95, and added one.? The chunk of schematic is the main bit.

You can check the OA95 (D4) by measuring some voltages with the power off, and with it on.

1)

With the power on, the 3V battery voltage shouldn't be significantly higher than with the power off.? If it is higher, the OA95 may be leaking.? You should see 5V at the cathode, and 3V or so at the anode - the end that connects to the positive terminal of the 3V battery, if it's not leaking.

2)

With the power off, you should see a voltage drop of 0.3V or a bit more, from the anode of the OA95 (battery end) to the cathode (RAM chip end).? Alternatively, measure the voltage at the supply pins of the RAM chips, and across the 3V battery.? If it's over 2V at the RAM chip supply pins, but a bit less than the 3V battery voltage, the OA95 is fine.

- I'm assuming you have a good battery.? If not, there could be a bigger difference in the battery voltage with the power off and with it on, which could confuse matters a little, but measuring the voltage from one end of the diode to the other, in each case, is still a good test. ? With the power off, it should be reverse biased and isolating the battery (cathode at a higher voltage than the anode).? With the power on, it should be forward biased, supplying power to the RAM chips (anode at a higher voltage than the cathode, probably by quite close to 0.3V).

The zener diode is a separate issue.? If the OA95 seems to be bad, replace it and see what happens then.

- Andy

No, zener diodes are a special type of diode, that's just made for a basic kind of voltage regulation.

Any small signal diode would do, for the 3V battery one, but since you're ordering one, it was originally a germanium diode - an OA95, according to the schematic, but any small germanium diode would work if you can't get one of those.

In the attached picture, you see it labelled as D4 - just above the middle, on the left.? The orientation is important - diodes have two different ends; an anode and a cathode.? They often have a stripe across the cathode end - which is shown pointing to the right, in the picture - pointing away from the positive terminal of the 3V battery.

An OA95 is a clear glass bead, with a red or dark coloured end, indicating the cathode - see attached example.

If you have a multimeter / test meter, you should be able to check continuity between the positive terminal of the 3V battery, and the clear end of your existing diode (the anode).

I don't have a picture of the physical location, but I would guess it's quite close to the battery.

- Andy

Hi guys,

I see.? I thought we were talking about the small diode that protects the backup battery from the 5V supply, and supplies power to the RAM chips when the supply it turned off - that one is a known culprit for losing the contents of the RAM, on a stock DX7.

- Andy