Early P1800 Rev Counter wanted

[asneddon]

My original Jensen Rev counter seems to be dead. The sender unit was missing so I tried hooking it up through a 12v to 12v transformer, and nothing. Then tried a direct hookup and nothing. I guess the sender using is something more complex. This is a single spade connector type. I haven't pulled it apart yet.

I've borrowed another earlier rev counter from Charlie at the Oxford Classic Volvo place and that would just spin around to full revs when power was supplied. Its a strange two spade connector one I couldn't find decent wiring diagrams for. I pulled it apart (with Charlies blessing) and its just a transformer hooked up to the electro magnet windings. No resistors or diodes in sight!

I'm now looking for a simple induction pickup type (The one where you wrap the low tension coil wire around the pickup) to see if I have any luck with that. Anyone have one around?

Thanks

[agent_strangelove]

If you can't find one locally, I may have one or two of the black box tachs about. If all else fails, you get a late '63 or '64 car and there was a small supplimental harness that hooked up to the coil and distributor (dizzy) and the tachs from those years read off that. Most of the folks that I know that have Jensen cars, had the black box sender unit go bad and went to a '63-64 tach with the additional bit of wire. I have done this on my own car (not a Jensen car but shortly after production moved back to Sweden) as it left the factory with a black box sender in the nose...


Chris

[asneddon]

Thanks. Can you tell me more about the supplimental harness?

The two spade connector rev counter I borrowed had one connector market + and the other was unmarked. I tried all the combinations of hooking it up I could think of:

+ to 12V, other to distributor
+ to distributor, other to 12V

coil to +, other to distributor
coil to -, other to distributior

Body earthed in all cases.

The action of the guage was always to ram at full speed over to max as soon as power was enabled (either through connection to battery or when ignition was turned on), or not to move at all.

The rev counter I still have is a 6000rpm red line one, and has one spade connector on the back, and one other connector that looks like a screw on clamp connector which is isolated from the guage body. I'll take photos some time. Ive never connected this second connection up to anything. My car is a 1963, but I dont know if its early or late in that year.

Allister

[asneddon]

I've attached some of the reference stuff Ive found.

the first two are from the Volvo service manual. Ive cut out all the other stuff as it was in the way.

The third one is stolen off the web. Sorry whoever I stole it from.

The last one came up on a google search and was interesting. Also stolen with no reference.

Hopefully this can help someone else

[agent_strangelove]

I can't promiss any info off the top of my head so I will wait till my car is in front of me. I will take some photos this evening when I am home and post them up...


Chris

[asneddon]

Here are some reference photos of the two types of tachs I've tried out.

[asneddon]

Just found this site! (busy day at work obviously)

http://www.volvosolutions.com/1800inst_tach.html

Looks like the tach I have in the car IS an induction pickup one, but missing the plastic bit to coil the cable around. I wonder if I killed it last night when I hooked 12V up to it! (probably is my guess).

Damn.

[agent_strangelove]

Well I think you have some of this figured out now...

I looked at my car this morning. There are two wires tapped off under my dash that are labled 'tach'. One is black (and is clearly part of the grounding on the car bu there is another black wire hooked to a mounting stud on the tach, so I'm sure the body of the tach is grounded) and the other is a black wire with a brown strip. The black brown one must be from the black box in the nose of the car.

At present, I have tach in there that has the small plastic block and white wire wrapped around it twice. This white runs from the spade clip (or small stud) on the side of your dizzy, up to the back of the tach, around the block twice and back down one of the studs on the coil. There is also a green wire in that supplimentry harness. The green wire is how your tach gets power. Thus mine is run from the protected side (fused) of the fuse box, to the spade connection on the back of the tach...

Attached are a few photos of the supplimentry harness with a tach and a couple of close ups of what is going on. The last one has a red wire for the dizzy/coil connection but you can see the block better.

If you need the block or the whole supplimentry harness, let me know.. Hope this all helps.

[asneddon]

I've been hacking away on the rev counter every now and again for the last couple of weeks. I ended up getting a later model (3rd Gen) rev counter (Wooden dash type) and the innards are all mounted on the same casting as the gen 1 and gen 2 rev counters.

I tried to get the face off the gen 3 and I was going to stick the face from the gen 1 I have, but I couldnt get it off without breaking it. So next I pulled the electronics out of the gen3, de-soldereing the two leads to the needle movement.

First idea was to run two cables from the gen3 guts to the two spade connectors on the gen1. This didnt work. I then dissconnected the coil thats inside the gen1 in series with the spade connectors and tried again (See last photo on post #6) . No luck. I'm not sure why this didnt work. It would have been nice as then you could use gen3 guts as a replacement for early Jensen sender units.

Next I stuck the Gen3 guts into the Gen1 I have. and soldered the gen1 needle movement onto the output of the Gen3 electronics.

I then ran a new (white) cable from the coil into the cockpit via the hole where the temperature guage senders go, into the 'frankenstein' rev counter, and then back out via the main wiring loom by the battery. I can get movement from the guage, but it jumps around like a mad thing and doesnt seem very accurate at all!

At this stage I realised I probably should have checked the Gen3 rev counter first before buggering about like this! I have no idea if the guage worked before I pulled it apart! Damn.

Also, the Gen3 guage seemed to have the electronics insulated from earth. The whole inner casting was protected via a rubber gasket against the guage outer body, and was joined via rubber insulated bolts. I couldn't get any movement without supplying an earth though. I'm not sure how this would have worked in the car. The casing needs an earth for the dash lights to work. There is a +12V to the guage, and the two connectors for the coil-distributor cable. These will switch to earth via the points, but they never connect to the electronics in the guage. They are just wrapped around an inductive pickup. If the electronics never have a path to earth then I dont see how anything works.

So, anyone have a working rev counter, preferably a Gen2?

[agent_strangelove]

It sounds like you are ready for your degree in electrical engineering after that fun....

I'm swamped with orders and shipping stuff right now but I will try to look at and test some tachs in the next couple of days. Do you care what the face/chrome looks like? Or are you just going to rip the guts out of it anyway?


Chris