I had to remove diodes D7 and D9 shown on the output schematic as part of circuit to control fuel pump and Fast Idle. Under some conditions with MS board off, a small amount of voltage will pass through D7 and attempt to power the MS board with power from the pump relay coil. I am also using the Fast Idle circuit, that has been modified, to control a fan which is always powered and has the same problem.
Both relays have spike protection and only about 100 ma is switched by Q3 and Q5.
After a year or more, no problems, but if these diodes have an important purpose I should know about, I would appreciate any help.
Thanks
Chandler
83 XJS V12 MS V2.2
Diodes D7 and D9
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Read the manual to see if your question is answered there before posting. Many users will not reply if the answer is already available in the manual.
If your question is about troubleshooting, configuration, or tuning, you MUST include your processor type (MS-I or MS-II) and code version in your post. If your question is about PCB assembly or modifications, you must also include the main board version number (1.01, 2.2 or 3.0).
If you have questions about MS1/Extra or MS2/Extra code configuration or tuning, please post them at www.msextra.com Such questions posted here will be moved to: a temporary MSextra sub-forum, where they will be removed after 7 days
The full forum rules are here: Forum Rules, be sure to read them all regularly.
Diodes D7 and D9
KC7EYZ
-
Matt Cramer
- Super Squirter
- Posts: 2951
- Joined: Sat Jul 03, 2004 11:35 am
Re: Diodes D7 and D9
They are to protect against flyback spikes when the relays shut off. You can replace them with 24 volt zener diodes that connect the output to ground - banded end towards the output.
