The Slash 5 starter
relay 'cricket' noise and starter problem
©
slash5cricket.htm, article 37
ALL /5 bikes should have this relay modification performed if it has not been already performed;....that is, if the original type of starter relay is there, do the modification!
The /5 bikes had a problem that manifested itself with either a slightly low battery, cold weather, OR BOTH. When the starter button was depressed, the 'starter relay' would not stay fully pulled-in to consistently close its contacts and thereby send electricity to the starter motor solenoid. Instead, it would, typically with starter solenoid noise contributing loudly, make a fast clicking noise, which was called the 'Cricket'. Every time the clicking/chattering starter relay closed, the starter solenoid might also partly energize. The effect was 'as if' the battery was quite low on vehicles you may be more familiar with, a loud chattering.
'Cricket' was a term put forward by "OAK" Okleshen, SEE ADDENDUM at the end of this article... and he did more than one article for BMW MOA News (now BMWON) on that problem, one reference to a fairly complete version will be found in the March 1977 issue of BMW News (further information in October 1977) (and a reprinted article April 1978), and an edited major excerpt will be found in the Chitech BMW Electric School Manual in Appendix F. ((BTW, that is THE best BMW airhead electrics manual ever published, and still available)).
NOTE: The below article includes a fair amount of additional information, from me, that was never put in the above articles.
The relay in question is a
metal can, under the fuel tank, on the left side, farthest forward.
CAUSE?.....>>>> The problem was
low amplification (low gain) of the transistor circuit inside the /5 starter
relay. That circuit was not temperature-compensated and the
circuit was also affected by battery voltage, which lowers with cold and with
inadequate charging. Since
energizing the starter motor will drop the battery voltage due to the very large
current drain during that cranking, the two problems tended to feed each other.
NO OTHER BMW but the /5 had this particular transistor type of circuit.
In the /5 this stock troublesome starter relay incorporates TWO functions.
Function #1: operates just like all the later airhead starter relays,
for sending electric power to the starter motor solenoid (which also incorporates a
very heavy duty switch/relay in itself.....THIS function is in ALL BMW
airheads).
Function #2: The additional function in the /5 (only) starter relay is
the transistor circuit to keep you from
being able to fire up the starter motor after the engine is running.
How this is accomplished will be described later. After the
/5, such things as a clutch switch and neutral switch are
interconnected to perform a purpose that is, truthfully, not up to the /5 protection
level in
regards to a running engine, but has other safety features.
Of course, the /5 had no such inter-protects
as a clutch switch at the bar or at the transmission, nor a neutral switch with
the same function as the 5 speed transmission models.
It is best to modify the original /5 starter relay unit so it operates under cold
and/or marginal battery situations. You can
do this yourself, or print the instructions and take it to your friendly
electronics shop. Note, that it is also probably proper to say
that the /5 starter relay is ALSO an anti-start relay, after the engine is
running.
Replacing with a generic relay or modifying to
remove transistor function on the original type of relay:
It is best
to modify the original /5 starter relay as described later in this
article. Once in awhile, that relay is such a mess that someone will
replace it. This might be from water damage, or an open coil.
The original type of relay is pricey, if you can find a new one. You could
probably find one from a salvage /5, and modify that relay. SOME will
choose to simply remove the bad relay and substitute a generic
relay. Almost any 12 volt coil relay with single pole single throw
contacts (SPST) will work just fine, and the Bosch black plastic cased ones,
cheap, most autoparts stores have them, will work.
It is possible, of course, to modify the
original /5 relay to eliminate the transistor circuit, but I do NOT
recommend that. That would be done by disconnecting the blue D+ wires, and
running the D+ terminal of that relay to ground. The use of a generic relay, or that
transistor circuit elimination modification allows the starter to be engaged at any time the
key switch is on, engine on or not. That is not
my favorite way of doing things.
HOWEVER, connecting either type of relay such that the key switch has to be ON
for operation, is fine.
If you plan to install a GENERIC relay, disconnect the blue
wires from the original /5 relay at the D+ terminal of that relay.
Join those wires, and insulate them.
Join the red wires that went to the original terminal #30 of the /5 relay, and
connect them to one contact of the new relay.
Connect the original black wire that went to terminal #87 of the /5 relay, to
the other contact of the new relay.
Now, the only connections left to install are to the new generic relay's
coil. One coil terminal must connect to the original brown-black
wire that was on the original /5 relay terminal #31.
How you now connect the remaining new relay coil terminal is up to you.
There are TWO methods to keep in mind.
1. If you connect the remaining relay coil terminal to a source of battery
power that is always ON, then ANYtime you press the start button, key turned on
or not, the engine will be rotated. This is a bad idea, but I have
seen folks do it.
2. The original wiring had terminal #15 supplied with power AFTER the key
switch was turned on. That is the connection to use. The associated
wire color is green-black.
Here is how that original transistor circuit operates in the /5:
The output of some of the small diodes on the diode board that supply the sensing voltage to the voltage regulator and the GEN
lamp
are also connected to this /5 starter relay at its terminal D+. Inside the relay can, a one-transistor circuit with an adjustable resistor (also called a potentiometer), drives
the relay that, in turn, fires up the starter motor solenoid. So, it is just a
simple transistor amplifying circuit
that was in the /5. The transistor circuit,
when turned on, drives the relay COIL, allows the coil to be operated by the
starter button. Conversely, the transistor is turned off by those alternator
small diodes output (once alternator is producing enough current at idle or
above), not allowing the coil to be energized.
BTW...trying to adjust that potentiometer should not be done.
FOR THE NERDY TECHNICAL TYPES: The
transistor is a PNP silicon type, probably a type BC213B or similar, with the
emitter connected to relay pin 15, thence going to the ignition
switch. The base goes to the pot wiper, one end of pot to emitter, other
end of pot to pin D+, which goes to the small diodes and voltage regulator and
lamp. The voltage regulator is slightly turned on when the key is on, and that
allows this point D+ to appear fairly low in resistance, via the rotor which
loads the regulator. The collector of the transistor goes to the
relay coil, and the other side of that coil, terminal 31b, goes to the starter
button. During key-on, engine not running, the transistor is supposed to be turned on,
via the regulator-rotor circuit, ALLOWING the relay coil to be
energized when the starter
button is depressed. In cold weather, perhaps combined with a slightly lower
battery voltage initially...and especially during attempts at cranking..... the transistor would not 'saturate', meaning it would not turn on fully.
Restating this slightly differently.....in cold weather the
gain of a simple uncompensated transistor circuit goes DOWN. At the same time the battery might actually be a wee bit down, and the voltage would be a
wee bit lower, making things even worse for that transistor, which is powered by the battery.
In actuality the circuit operation is a slight bit more complicated, in how the
transistor is operated, but that is good enough for this discussion.
The 'fix', as originally outlined by OAK, is to remove the relay from the /5, open it up, and make a simple modification.
I HIGHLY recommend AGAINST trying to do the modification with the relay still on the bike. Be
SURE to disconnect the battery before touching or removing the relay.
DO NOT do this job yourself if you are the ham-fisted type! NOTE where the wires
go when removing the relay, your bike could have been modified, or have an anomaly. The relay
bottom has the connectors numbered, you can make notes or a sketch, or
whatever.
NOTE!....The innards of this relay can be installed 180°
around. Therefore, before uncrimping and removing the innards, be SURE to
MARK, somehow, the relay can and the relay base, so they are installed the
correct way 'round.....thus the wires on the bike will fit properly when
reinstalling the relay onto the bike backbone.
Bike wiring: blue wires connected to the
two D+ terminals; Green/black to
15; red to 30 (there are TWO
#30, they are identical in connection and function); black to 87; and
brown/black to 31b.
THE Modification/Fix:
The modification fix is to remove that small adjustable
resistor (potentiometer) entirely and add two cheap parts.
For access to the inside of the relay, you must UNcrimp the cover. Do this NEATLY, and recrimp it
back in place when you are done...NEATLY, and with the innards in the correction position.
Parts: You may well be able to have the local TV shop give
you these parts from their junk box. NOTHING critical about them at all.
Part #1: A commonly available 470 ohm 1/2 watt (or 1/3 or even 1/4 watt) resistor
will be installed and connected to terminal D+ inside the relay can on the
circuit board, and the other
end of that resistor to the transistor BASE terminal (BASE describes an
electrical function, not a physical location, although it IS on the bottom of
the part. A simple transistor usually has three leads, called base,
emitter, collector). These
resistors usually come with bands of colors on them, the bands signifying the
value in ohms. For the 470 ohm resistor, the first band, always the one
closest to one end, is yellow (4); the second band is violet (7); and
the third band is brown (signifying zeroes, in this case brown means ONE zero). There may be another band,
typically it is silver or gold, signifying percentage tolerance.....disregard
that, it is of no importance. Radio Shack probably still sells 5 of
these in a package for 50 cents under part 271-1115 for the 1/2 watt, or
271-1317 for the 1/4 watt. When bending the resistor leads try not to bend
too close to the resistor body, which might strain the part.
Part #2: A common silicon diode, any type (generally, so long as it is
not called a Schotky, NOR called a ZENER), and it may be rated from 1
ampere to as much as 2-1/2 amperes (anything larger is hard to fit), any voltage rating, is connected, circuit-wise, from
the BASE of the transistor to the EMITTER of the transistor. You MUST connect the diode so the END of the diode that has the LINE
(painted band) on it connects to the EMITTER. NOTE!!...This is all done at/on
the original circuit board potentiometer mounting and connecting holes, and NOT
at the transistor part leads Radio Shack probably still sells
packages of 2 of these common diodes under part number 276-1101 (up to
-1104)...any of these are OK. Packages of two are probably under a dollar.
Whatever or wherever you obtain this diode, the diode might have an arrow and line
printed on it, or just the line. The line is closer to one end of the
part, signifies the end wire that connects internally to the cathode of the
diode (arrow, if present, is anode), and it is the LINE end you will be
concerned with.
Warning!!! Be
very careful in removing the potentiometer. It will NOT be reused, but you do not want to damage the coil wires. It is best to use a product
called Solder Wick, or similar solder-sucking braid, with some extra soldering rosin, to soak up the solder around
the three potentiometer leg leads, and then with the soldering iron back on those leads
one by one, bend the potentiometer lead vertical with a small sharp knife blade. Then snip the
lead flush with the board on the soldering side, which shortens the lead for ease of pot removal from the other side,
and then GENTLY remove the pot, probably with narrow long-nose pliers or
forceps, from the other side of the board. Be
VERY careful not to nick or break the COIL wires!!
This is a picture of a stock, UNmodified /5 starter relay, removed from its can.
When YOU did this, did you remember to FIRST mark the innards base and the metal
can, to fit the innards back in the same position?
Note that you can see the potentiometer screwdriver slot in the small hole.
Below is a top view of the stock, UNmodified /5 starter relay, with the
potentiometer
in the lower center area, and the black cylindrical transistor on
the right.
This is a picture of a modified /5 starter relay, and to the
right is a similar potentiometer as you will be removing, but with original
length leads (you will be cutting them before removing the potentiometer, per
notes herein).
The resistor is in the center upper area.
The diode, which in this lousy photo
appears to be a silvery line, directly below it.
Note that the resistor RIGHT wire and the diode RIGHT wire (anode) connect to
the same point.
The line end of the diode, called the cathode (the flash reflection makes it
hard to see) is to the left side.
Before you assemble to the can and re-crimp, burnish the relay contacts. You can use a very fine grit sandpaper (or a points file or contact burnishing tool) for that, perhaps 360 grit or even finer grit. Burnish both contacts. Do NOT change the gap distance. Use your fingertip to put a SLIGHT amount of pressure on the sandpaper, then turn the sandpaper over and repeat for the opposing contact. Slide a piece of clean white paper through the contacts (hold them with slight pressure with a fingertip), to clean off any grit. If you decide to seal the can using something like RTV, do NOT use the type of RTV that has that smelly acetic-acid component!...it can cause the contacts to develop an insulating film, or even corrode things. IF you use a sealant, use only a small amount of sealant, on the edge of the board, as you insert the innards....AND... be sure to line up your marks so as to put the innards back in correct position in the metal can. If you do not, the wires MAY not fit easily.
Testing the unit....for the technically
nerdy (do NOT do this unless competent!):
The stock /5 relay (or modified /5 relay) can be tested in several ways.
Here are reasonable methods of testing, with the
unit off and disconnected from the bike's wiring; or, on the bike, with all blue
or other wires on terminal D+ disconnected:
1. Apply +12 volts, approximately, from an external power supply, or if in
the bike via turning on the key, to terminals 15 AND 30 (in bike, the key being
turned on will do that jumpering and apply +12 to both terminals).
2. Connect a lamp or other low power load between terminal 37 and the minus
supply (if still wired to bike, the starter is wired there, leave as is, no lamp
needed).
If off the bike, connect lamp to both 87 and 31b and connect terminal 31b/87 to the minus supply.
3. When terminal D+ (if in bike, you DO have the blue wires off it?) is
connected to +12 (or terminal 15 or 30 in the case of relay still connected in
bike) the lamp must not be lit. If terminal D+ is not connected to
anything, the lamp must still be off.
4. When terminal D+ is connected to -12v...in the bike that means grounded
or to 31b, the lamp must light....or, in
bike, starter operate.
Revisions:
First posted to Airheads LIST about 8 pm on 07/24/2003. Then edited, and
put here about 9 pm, and edited for references.
07/27/2003: final editing and release
09/30/2003: slight clarifications and references.
02/04/2004: Update in preparation for pictures
02/05/2004: pictures and text, article completed
02/06/2004: Final edit and release
03/23/2004: edit for clarity. NO important changes.
11/20/2004: Revise extensively to eliminate problems in understanding the
procedure IF using a generic relay, and not the original type of relay (whether
modified or not). Add information to make it just about impossible to
misinterpret the modifications, no matter if /5 relay or generic relay.
02/25/2005: minor cleanups and reduce contrast on one photo