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Well, this is how I fixed mine - hopefully it helps a few more people down the line. Having done a bit of reading I suspect a lot of people have suffered from this very problem, but I have yet to see a fix posted, so hopefully I\'ve filled a gap.

As you can see in this thead:

http://m.rx7club.com/forum/showthread.php?p=9967007

post number 10 by MR_Rick shows the internals of the tacho and the broken components that lead to instrument failure. The big electrolytic capacitor and the four Zener diodes, plus one of the smaller caps all needed replacing in mine, but I\'d imagine may vary instrument to instrument. Spotting component failure is often easier than you might think as they often leave telltales. The caps will either mushroom up on the top of the can - if they\'re convex they\'re broken - or you will see black marks on the solder joints below where the magic smoke has escaped. Broken zeners and transistors can be spotted similarly by black marks on their solder pads as well as cracked casings and discolouration on the PCB beneath. To save the pain of trying to read the zener values, left to right, they are 4.7, 5.1 and 5.1 in the picture mentioned above. These appear to be used as crude voltage regulators for the speedo and tacho, hence the failure of both as the speedo feeds the tacho. The 1000u cap is vulnerable, as are any of the other can type caps. Replace as you deem fit for a few pence worth of components and enjoy a working rev counter and speedo again. I\'d recommend 1.3W zeners and 105 degree caps. Mount the zeners away from the board a little to aid cooling.

For those not familiar with PCB work, replacing a component can be tricky, so I\'ll give the following tips:

Use at least a 50W iron. Some of the solder pads are on large areas of copper and sink a lot of heat away, so this is an absolute necessity.

Clip the components off their leads and unsolder them seperately. Mazda saw fit to bend the leads over onto the pads so there\'s an art to unsoldering them with the component still attached. Make life easy for yourself.

Do not pull hard on component legs! Wait until the solder is molten right the way through the hole and it will come out quite nicely. Pulling legs out will result in the plating in the via coming out with it and ruining the PCB (unless you\'re very clever).

If the solder doesn\'t want to melt nicely, add some fresh. This might seem counter intuitive adding solder to something you\'re trying to remove, but fresh flux and non-oxidized solder helps transfer heat.

Lol. Likewise, I was attracted to the rotary because it\'s different and I like a challenge. I tried to love it, and even went as far as doing a (successful) rebuild myself. I feel I have fair grounds for saying after all I\'ve been through with it, I simply don\'t like the Mazda rotary. If it floats your boat fair enough, but just not my cup of tea at all.
I have a car I like that owes a fair bit of money with an engine I have no love for. It\'s currently running very well, but I can\'t stand the \'what\'s it going to do today\' fear when wielding the key :rollin
For one reason or another (to be fair, not all rotary related) it doesn\'t look likely I\'ll be getting my money back out, so why not sell the rotary, take up the challenge and do something different with it :3gears-lh
There are my reasons for considering a conversion anyway.
The Audi was the other way around btw - Fell in love with the engine, but didn\'t really like the car in the end.

I sold an FD with no engine a while back and I didn\'t have a single serious call from someone that wanted to put a rotary back in, despite it actually being registered as a 1.3 and pre cat requirement. Even I was fairly shocked.
I take your point on the V8 - that wouldn\'t be my thing either - but I feel the smallish turbo I5 isn\'t too out of sorts compared to many other options. At least it\'s not a 2.0 turbo 4 pot It does have one other thing going for it that really appeals to me: Never been done before. :Giggle

Audi 2.2 I5 turbo Shorter, way lighter that the 1JZ, capeable of the same power, but bombproof with it. I\'m still measuring up and musing, but looks like it\'ll fit in really nicely with no steering rack or bonnet issues. My S4 that the 5 sylinder came out of returned 30mpg rolling average on a mix of motorway and town despite weighing twice what the rex does, and an easy 40 if driven sensibly on the motorway too.

http://www.rx7club.com/showthread.php?t=809261

I don\'t think this is the thread, but I remember now that BDC is the guy to look for posts from. He really knows his stuff. Again, good luck dude

Hello chap. Sounds like you\'re heading in the right direction. If I remember correctly, running with less split has a similar effect to advancing the lead timing. There\'s a massive write up on rx7club.com that gets really technical. It will answer all your questions if you can find it. Good luck! Will post if I do find it.

I had this annoying issue on mine. I changed the sensor, checked continuity through the whole loom, cleaned contacts. Nothing fixed it. Eventually I changed the dash - specifically the speedometer, as that\'s where the signal path eventually ends, and where it does the measuring - and the problem has gone away.

£30 if you want to come and pick it up? Havant isn\'t far from Basingstoke if you\'ve got another car to make the trip up one evening? Otherwise, £15.50 express48, or £20.50 for express24.

No problem. Just let me know.

You could also have a look at the fuel pump wiring and the speed control relay as it\'s load related. Check the voltage you\'re getting at the pump, the top of which is pretty easy to get to in the boot. You can bypass the speed control relay with a piece of wire and two crimps to check if that fixes the problem (the diagram on the top of the relay will tell you which terminals need to be shorted together). It\'s only there to cut the pump speed down at low load. There\'s a resistor in the pump circuit to drop some voltage before the pump, and the speed relay shorts it to bypass it and give the pump full votage. Just shout if you need any more detail.
Could also be the pump itself, the pressure regulator, or the vac line to it, but depends on your setup. HTH

You got any pics you can post? I do all my own work, but I normally take the bits I\'m about to use to one of the guys that lives and breathes rotary for a final opinion.
Opinion does seem divided on lapping. Some people do, some don\'t. Have you got a dial gauge to check the depth of the scoring on the plates? It _shouldn\'t_ be hard to get them lapped true - the plates have machined surfaces on both sides don\'t forget. Any competent machinist will be able to set a machine up so that the deck stays flat and true. The thickness of the coating is a different matter, however.

I\'m pretty sure you\'ve got a faulty alternator. Running one without the battery as ballast (yanking the terminal when you couldn\'t get her to stop) tends to kill them. I do have a couple of spares which you\'re welcome to try to confirm though.

Write up for configuring for single turbo rotary. Very comprehensive:

http://www.aaroncake.net/RX-7/megasquirt/index.asp

He\'s using the Megasquirt 2 processor, and version 3 of the circuit board.

No worries. A good place to start for anyone that\'s curious is the tuning software:

You can tell a lot about the features of any ECU and how it works by just browsing through the config menus. In this case, Tunerstudio:

http://www.efianalytics.com/TunerStudio/beta/

And there used to be a good MS on rotary write up on the yank forum, plus a whole section on MS related issues.

Please do

Lol. I often do wonder what posessed them to call it that

Anyway, yes, I\'ve installed it on quite a few cars. It works, it\'s cheap, it\'s full standalone and packed with features.
I\'m actually about to do an install in an S1 Elise this afternoon.
BUT, it\'s not for the faint hearted. You will need some technical skills to do a decent install, as it\'s not like the apexi that you can just plug and and let it settle down, and ity won\'t run the sequential twins. Rotary support is supposed to be pretty good, as one of the guys who develops the project is a rotary nut. I\'ve not tried it on a rotary myself though.
If you want to know anything I\'m happy to answer any questions. The MS rotary scene in the states is quite big, but there aren\'t many in the UK that I know of who\'ve given it a go..