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Post by wrecker on Aug 3, 2005 17:17:33 GMT
I guys, I need some help, I aquired a revs counter for the olde girl but it's positive earth is there a simple way around this if so diagrams please (I am stupid) Or do I have to send it away to be done, has anybody had this done, if so how much does it cost and how long does it take, where is the best place to go to? I do already have a rev counter but as soon as I put the P5 lump in the Landrover it broke and got stuck at 1000rpm, it's only one of those crappy £24 ones, I much prefer the Rover one and would like to fit it. Cheers Adam
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Post by darryl on Oct 23, 2005 14:08:38 GMT
Hi Adam, Did you get this sorted? If not I may be able to help Rgds
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Post by dorsetflyer on Oct 23, 2005 18:50:14 GMT
I have a similar problem on mine. It's quite happy going up but refuses to go below 1000rpm even when the engine is switched off. Tapping the glass sometimes will make it go just below the 1000 mark, but not every time. I have had it out twice now, stripped it down and applied a little sewing machine oil to the spindle bearings. this has loosened it a bit but it still feels tight when you let go the spring tension having wound the needle up the scale. It's certainly better than it was so I'll leave it alone for awhile. As regards the polarity I'm not sure how that can be changed.
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Deleted
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Post by Deleted on Oct 24, 2005 7:48:52 GMT
Try : Robert Fenn, Vernham Dean, Andover, Hants 01264-737717
or John Ostick, 34 spring Avenue, Keighley, W Yorks 01535-662701
Both offer instrument repairs and quick turnaround, with fair prices
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Post by dorsetflyer on Oct 24, 2005 14:32:38 GMT
Thanks for that Freddy, I'll give them a bell and see what transpires.
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Post by Phil Nottingham on Oct 28, 2005 19:20:04 GMT
Speedograph - Nottingham also do them although I understand they are bit pricey
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Post by Ken Nelson on Apr 23, 2007 1:10:31 GMT
Having gotten my 1966 P5 Coupe on the road, I would like to get the tach to work properly if that's possible, and perhaps to convert to negative ground. I see a lot of posts about all of the tachs being unreliable due to age and transister breakdown. Has anyone come up with a solution so far? Ken
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Post by Phil Nottingham on Apr 23, 2007 16:20:24 GMT
If you folllow the thread - I think someone has rebuilt them - the majot UK instrument repairers certainly will be able to sort these out - at a price. If yours had been a MK3 ity would have been negative earth (ground)
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Post by Deleted on Aug 8, 2007 21:58:41 GMT
If the meter sticks, try spraying the movement with switchcleaner. It can't do any damage, as the only other solution is to get it repaired professionally-probably expensive. With old transistor gear the only things that go are usually the electrolytic capacitors and the transistors. Transistors of this vintage were germanium types, which do fail. modern ones are silicon,which don't, but were for different polarity. Tip- buy old british tranny from bootfair and remove transistors. You only need 2, most types should work. All this assumes some working knowledge of simple radio repairing, but most owners should know somebody I am sure. It is also fairly easy to accurately calibrate this type of tacho using a battery charger (not the posh electronic type, but the simple garage sort).If anyone wants to try this i will post the instructions. It worked very well on my one.
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Post by Phil Nottingham on Aug 8, 2007 22:22:39 GMT
Sounds interesting - mine needs recalibrating or otherwise the engine doing twice its design revs at top speed.
Can you send me some instructions please? +ve earth
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Post by Warwick (Ozcoupe) on Aug 9, 2007 3:32:17 GMT
Me too. My late model negative earth tacho reads high and off-scale at highway speeds. I haven't had a chance to investigate yet but had assumed it was due to presence of Lumenition in distributor (although I thought this would have made it read low or not at all), or the presence of a non-standard alternator. I haven't yet been able to find where the pick-up point is.
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Post by johnwp5bcoupe on Aug 9, 2007 5:56:10 GMT
Rev counters work on pulse count either active or passive I have not looked at the P5b one but I will investigate and draw out the circuit for future reference In regards to djoldboys comments of replacing transistors there were/are a vast array of PNP NPN types signal/power different gains current handling etc etc so I would not recommend changing unless it is the same or a known direct equivalent
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Post by Deleted on Aug 9, 2007 10:09:55 GMT
In Derby we are lucky to have R.F. Potts in Babbington Lane, a real old fashioned electronics place. I took the transistors, diodes and resistors etc out of my tacho and they identified / sold me new resistors and the modern equivalent transistors and diodes. I simply soldered these in place and re-calibrated the unit against a portable engine tuner (with revcounter readout) and Robert is your mothers brother! (Bobs your uncle!)
This only works if the movement is working OK.
Regards
Freddy
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Post by Phil Nottingham on Aug 9, 2007 11:05:05 GMT
There is pick up point as such its an inductive loop on the ignition supply - use SEARCH set to 1000 days for 200 posts and see some pictures I posted once. A lot has been written about this topic and SEARCH picks up most. Many viewers looking for things do not notice the days are default set for 7 with a max of 10 posts
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Post by Warwick (Ozcoupe) on Aug 9, 2007 12:16:50 GMT
There is pick up point as such its an inductive loop on the ignition supply - use SEARCH set to 1000 days for 200 posts and see some pictures I posted once. A lot has been written about this topic and SEARCH picks up most. Many viewers looking for things do not notice the days are default set for 7 with a max of 10 posts Yep thanks Phil and John. I should have explained further. I did ask this question a couple of months ago and did the search, found the previous advice and photos. (Also got a wiring diagram scan from John). My problem is at the other end. The wiring at the distributor end isn't original and doesn't look anything like the diagram. I'll know more once I have time to get in behind the dash and follow some wires and gut out everything that doesn't belong or looks iffy. I guess I've been asking questions in advance to increase my knowledge in the meantime, but I probably should wait until I have more "on car" experience and have specific questions to problems I encounter. Not fair really since it can waste others' time answering or repeating advice to very broad questions. My only excuse is that I'm impatient to get driving and I have less interesting problems to deal with first.
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Post by Phil Nottingham on Aug 9, 2007 14:24:35 GMT
I do not think its wasting other's time - not certain anyway whether the wiring at the other end makes any difference, as long as only one ignition fed supply goes to the coil the inductive type fitted to P5's will work
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Post by Deleted on Jun 5, 2008 19:06:12 GMT
This may have sent earlier, incomplete, due to laptop having a mind of it's own! To check the accuracy of the tacho on the 3ltr. Remove the power lead from the coil. connect a cheapo batt charger to the power lead. Turn on ign. Tach will read 2000rpm. There is an adjuster inside the instrument if necessary. The operation takes about 1 min. Will not work with a super dooper electronic charger. It is possible that some chargers will only give a reading of 1000rpm, but it should be obvious which one it is. The accuracy of this method is the accuracy of the 50hz mains, which is very high.
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Post by Phil Nottingham on Jun 5, 2008 19:32:25 GMT
Good tip - problem is with older ones is that as they warm up they read higher and higher!
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Post by johnwp5bcoupe on Jun 5, 2008 20:01:07 GMT
Be careful have you checked the voltage on some battery chargers and some are very crude with the smoothing
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