DME Update Questions
 

I am installing a Steve Wong chip that requires a 4K DME. I have the instructions to convert my 2K to 4K but have never soldered a circuit board. Anyone ever done this that can give insight? I am assuming that you heat the solder on the back side and install the jumper wire. I looked on Steve Wong's web sight and he shows a picture of the back side after completed.

I just need some guidance. Thanks. Joe


Here is the picture from SW site after
install
http://forums.pelicanparts.com/uploa...1427941426.jpg

And here is mine before and mods

http://forums.pelicanparts.com/uploa...1427941789.jpg

Get a solder sucker tool, some fine electrical solder and a good solder wand.

Open up a dead old radio or pc board and practice.

Plug in the wand to heat it up.
Once Hot, place it on a old solder and use the sucker to remove the old solder.
Cut a practice piece of wire and place at the joint and place the solder gun on the joint and wire to heat it up then use the solder wire.
Place the solder end on the wire and joint, NOT ON THE WAND. Caution it will melt instantly so be prepared and move toward the soldering joint/wire.

Practice some more.

Watch a you tube video for more reference, then go for it.

Once you feel comfortable tackle the DME.

If you feel at all insecure, send it to Steve and have him do it and check the entire DME while he is in there and fix anything that needs it.

Just my 2 cents,

Jim

Ask Ingo Schmitz, he's a soldering savant. Personally, I would send it to him to be evaluated under magnification for any fractures or evidence of possible future cracks in the solder joints throughout the circuit board.

Meh, it's not that hard. Use a hot iron - idea is to heat the solder quickly. Take a long time and the heat gets into the components, which is something you want to avoid. Start with a clean tip, then tin the tip with a little solder, that'll help make a good "bridge" to transfer heat quickly.

To make a good joint when you're soldering things together, you heat the wire and let the solder melt in, rather than try and pack solder on top of cold wire.

There's a little bit of an art to it, but it's nowhere near as hard as, say, welding.

What happens if you install a chip for 4K on a 2K board?

There are jumpers on the board that control if it is using a 24 pin or 28 pin chip. Obviously you must also add the chip socket to accommodate the extra four pins.
But if you had the socket to connect the chip and it was still jumpered for 24 pins it wouldn't run. It would basically be fed random junk as maps for the CPU.

The chip is a 24 pin and the board is a 24 pin. If I understand correctly they changed the board to 4K from 2K but kept the 24 pin until mid 1986. Am I mistaken?

Am I missing something. Yours board looks the same as the circled areas.
I've got SW 24 pin chip in my '86 without requiring any modification

I thought it was plug and play also but the paperwork says that the chip was made for a 24 pin 4K board and if your board is 2K, which mine is, it needs to be converted with an enclosed jumper wire. My question now is, will it not run properly if I don't convert the board?

Circuit boards sometimes have a conformal coating that can be present on either side.
Scrape the area to be soldered upon with a exacto knife to have only solder present, the coating will foul the solder iron tip and lead to overheated components if not removed prior to soldering.

Best to ask Steve Wong that question.

Yes... It need to be converted as per SW instruction.

If you don't feel comfortable to do it and there is nothing wrong with that..., just post your location (Whispering Pines, NC) and some close by Pelican that would be comfortable with doing it for you, would probably trade a few Brewsky for their time :D:):D

Ingo.
 

Ingo is the man.

As he did for me, he may be able to help you by email.

pcarsba@gmail.com;
^^^^
Ingo

Good luck,

Gerry

It simply won't start if you don't do the 4k conversion.

I found moving the jumper was a lot easier with a helper. One person pulling up on the jumper with a pair of tweezers while the other person held and heated the solder point. Minimized the heating time.

Need to clear some things up...
24 pin IS 2k
28 pin IS 4K

You absolutely need to change the board jumpers to switch from one to another. The different chips have different use of pins and if you don't change the jumpers it WILL NOT be able to use the chip.

The biggest example of the difference:
The processor chip built into the DME has the programming code that the DME runs burnt into it. (This is a different chip from the chip that is replaced when doing a "chip change") The 28 pin chip includes new program code so one of the required changes is a jumper that tells the processor to ignore its built in program and to go to the chip and run the program it finds there. The new program allows the DME to use updated maps to get smoother performance.

So no update of jumper equals unable to read maps. And if you have it jumpered for 28 pin and put in a 24 pin you are telling the processor to run a program that isn't there so: BONK!

Do as Driven97 said... another tip if your new to soldering, skip the solder sucker and buy this instead Fine Braid Solder Wick #2 Yellow - 5ft - - Amazon.com
it will remove all the old solder and you wont burn the devel out of your board in the process.

Send it to Ingo, he will check the whole board out, resolder any bad connections, install the new socket, and even burn you a new stock chip for the bigger socket!

Let me try to clear up some confusion:

There are different two 24-pin EPROMs out there and not all are 2k. The very first rendition of the 3.2 Motronic used a 2716 with 2kx8 capacity. The base code is located in the CPU and the EPROM contains personalization (maps, calibration, high-level routines)

At some point with the EPROM development moving forward the 27C32 with 4kx8 space and still 24 pins was used by Bosch. The code initially didn't make use of the addition space and two identical 2k-sized copies resided in the 4k EPROM. The base code was still in the CPU. Later versions used the full 4k of the EPROM.

Then once again the the 27C32 EPROM was replaced by the 27C64 EPROM with 8kx8 space and 28 pins. Now the entire code now resides in the EPROM and the internal code of the CPU is disabled.

The jumpers account for the different 24-pin versions of the EPROM. Pin 21 needs to be Vcc for the 2716 to function properly and A11 for the 27C32 IF it is a real 4k later version. The other important thing to keep in mind is that most modern chips now come in a much larger EPROM (27C512) and there should be 8 identical copies inside so the jumpering doesn't matter. The 27C512 is the only EPROM currently still in production. If the chip is in any other EPROM it is a "pull" that has been erased. In other words its an old device that has been sourced somewhere on the used market.

Best,
Ingo

Actually, the 27C32 (CMOS version EPROM) was not used by Porsche/Bosch in any 911 3.2 DMEs.

So it was a 2732 - completely irrelevant for the discussion above - What's your point, Loren??


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