Weird Tach Behaviour

[kz]

Hi again,

Have been travelling for a couple of days...

Your board looks the same as mine

[kz]

Tv, you can always try to change all components exept f?r the IC-circuit by chance, the components are not expensive. you can also try to resolder everything.

and you could check if the board itself has any cracks.

If you have a signal generator you could test the tacho and see if it works then it's not mounted in the bike.

An other solution could be to find a modern chip and redesign the tachboard.

Has anybody figured out what chip the main IC is on the board?

[Tv]

Hi kz
I've changed those two caps as suggested in the previous posts but still no go. Tomorrow I'm taking the unit to a shop to get it checked. I'll let you know whatever I find out
REgards
Tv

[Bolder Biker]

Hi Tv:

There are a number of us who will be interested in the result of the shop's investigations. I was fortunate enough to have been given a NOS instrument pod for my 1983 GS750ES (same looking board as yours) but I would still like ti fix the original one as a spare.

BTW, Hi kz......nice to see you here again!

BB

[Tv]

G'day All, I'm back from the shop

The techniciian reckons the circuit board is OK but he re soldered the main chip just in case. Upon test the tach was still behaving in the same manner ie. would rev to 2000 at variable pulses but given a huge dose of power, only display 6000 revs and when power off slowly come back to around 2000 so he opened up the tach needle mechanism which is packed with a silicon type grease, removed the grease and repacked with a lighter grade grease. He reckon the grease can go a bit gooey over time and possibly inhibit the tach needle movement.
I hope to install tach tomorrow to find out whether OK. I'm doing other work on the bike so it may be a cuppla days before I can properly test the tach
REgards
Tony

[Tv]

Success - Tach works!
So changing the silicon based grease to a lighter grade after cleaning out the old grease seems to do the trick. I didn't actually see the tech do the job but he pointed to the retaining bolt at the back of the tach needle mechanism and said the grease is in there.

If anyone has an old beater tach they might wanna share a little more detail about the fix after they've performed the same trick.

best of luck an Regards
Tony

[DMPLATT]

Ok, more details please. Exactly Where is this grease?

Interesting. I did the component swap as well, it will sometimes get over 6k, but not often. However, upto about 5500 it works great.

Interesting.

[Tv]

Where is the grease? I didn't see the techniciian dismantle the unit but as he was explaining what he did, he was pointing to the small (brass)nut on the back of the tach drive unit. I assume if you remove the nut, you will be able to then remove the needle and shaft from the tach. I think this is where he said the grease was. It might be wise to mark the positions of the parts before you disassemble or you may upset the zero position of the needle.

I have yet to road test but in the shed everythibg looks positive.
Good luck and let us know how you go
regards
Tv

[DMPLATT]

Thanks for the info.
Not sure if and when I'll get to that. As of now, except the Tach Fluff issue, my instruments work great. I won't dig into them just for that. But I'll surely give it a try if and when I do tear into the cluster again.

Keep us updated.

Later.

[Darter]

First I would like to say that I have had my bike a little over a year and everyone on here who has posted has helped me out tremendously. I finally need to ask a question though.

I am working on changing the two capacitors on my tach board and upon taking it apart I noticed the little gray thing looks cracked. So I want to replace it while I have everything apart. I only knew what the capacitors looked like because of the picture above. So what is the gray thing. I apprectiate any help.