TTI 1906 DMM teardown and low current range repair - Page 1
Forum section: electronics / repair

author: h.bashar
author_rank: Contributor
timestamp: August 27, 2016, 12:00:34 am
content: Hi folks, received my latest win from eBay today, a TTI 5.5 digit DMM with 0.012% basic DC accuracy, the low Amp range was showing overload in all ranges (DC and AC) while the 10 Amp range was working fine so I took it apart and after consulting the service manual and some probing traced the fault to an n-channel mosfet (ZVN3306A) designated F6 in the input circuit around the low amp current sense resistor, this was removed and the meter was tested and it worked fineexcept for the uA range because I didn't have a replacement mosfet (will order soon).I hope this will be useful for someone.Best wishesHasanain

author: Muttley Snickers
author_rank: Unknown
timestamp: August 27, 2016, 01:16:23 am
content: NiceAlthough the document below is still a work in progress, in its current form it may be of some assistance to you and I'm about to complete the other selections such as resistance and current, I spent a day trying to get this meter to a usable state and am now satisfied with the results, if you need the document in PDF form I could arrange that as well.This worked for me so I documented it for future reference, not entirely complete or accurate but a good start.

author: h.bashar
author_rank: Contributor
timestamp: August 27, 2016, 11:21:47 am
content: Quote from: Muttley Snickers on August 27, 2016, 01:16:23 amThanks!, the document you attached is very detailed and will come handy when calibrating the meter, about the serial xon and xoff lines this could be why the meter is hanging after awhile on R232 comms probably of the timing when using a usb to RS232 chip? I haven't tested the RS232 comms yet and I have a physical RS232 port on one of my laptops so will give that a go and let you know how it went.

author: h.bashar
author_rank: Contributor
timestamp: August 27, 2016, 11:36:24 am
content: Cant seem to find a place on the web to downlaod the TTI arc windows software, is there a free version of it?

author: Muttley Snickers
author_rank: Unknown
timestamp: August 27, 2016, 11:53:43 am
content: Quote from: h.bashar on August 27, 2016, 11:36:24 amTry this link below and whilst there grab everything you can, I regret not having the dismantling instructions for the case beforehand but it looks like you mastered it already, I broke two tabs which were half buggered anyway.Also the laptop I used had an onboard serial port so no USB to serial adapters and this was my first closed case calibration sequence which is probably basic stuff for those in the know but as you can see I did have a few headaches initially.TTI Downloads.http://tti1.co.uk/downloads-tti.htm

author: h.bashar
author_rank: Contributor
timestamp: August 27, 2016, 12:04:20 pm
content: Quote from: Muttley Snickers on August 27, 2016, 11:53:43 amThanks for the link, I will try the software soon and let you know about the serial handshaking status.

author: DTJ
author_rank: Super Contributor
timestamp: August 27, 2016, 12:34:17 pm
content: Do you need pdf copies of the service & operation manuals for the 1906?

author: h.bashar
author_rank: Contributor
timestamp: August 27, 2016, 04:23:53 pm
content: Quote from: DTJ on August 27, 2016, 12:34:17 pmAlready got them of the internet but thanks

author: h.bashar
author_rank: Contributor
timestamp: August 27, 2016, 04:58:28 pm
content: Quote from: Muttley Snickers on August 27, 2016, 11:53:43 amI tried using the interface with a standard serial wire, ARC software didn't work but managed to put the meter in listen mode using a 3rd party serial software but got no replies, It appears I will need a custom cable made for the serial interface

author: Muttley Snickers
author_rank: Unknown
timestamp: August 27, 2016, 11:07:01 pm
content: Yes, as I mentioned in the word document I spent a day on this meter and the majority of that was establishing reliable communications between the meter and the laptop, the software is a bit buggy and the custom cable is essential.No doubt you will read the service manual numerous times and then follow it to the letter as I did without much success, hence the creation of the cheat sheet which if followed should save you the numerous hurdles I encountered, feel free to add your own findings as I will admit up front this was a new experience for me with equipment, software and procedures I was not familiar with.For those seeking the TTI Arcwin or Arctalk Software I have posted them in another thread on this forum.Linked Here

author: h.bashar
author_rank: Contributor
timestamp: August 28, 2016, 12:41:38 am
content: Quote from: Muttley Snickers on August 27, 2016, 11:07:01 pmHave you tried this software under win7?

author: Muttley Snickers
author_rank: Unknown
timestamp: August 28, 2016, 01:00:18 am
content: Not yet, I had been waiting on reference resistors to arrive to continue the process and just got hold of a variac to check and maybe adjust the AC, on mine the main concern was the DC voltage which is now in complete agreement with both a voltage reference and some other meters I have.The meter needed to prove itself before I would commit to any further effort or outlay and to simply take it to the calibration lab before that in my view would have been a mistake should a hardware issue not have been identified beforehand, as it is I am very satisfied with the meter and now have the ability and equipment to make adjustments if necessary.

author: h.bashar
author_rank: Contributor
timestamp: August 28, 2016, 01:08:13 am
content: Quote from: Muttley Snickers on August 28, 2016, 01:00:18 amfair enough, I was looking around for reference resistors to check the ranges on my meters what sort of resistance precision is required to verify in this sort of instrument?

author: Muttley Snickers
author_rank: Unknown
timestamp: August 28, 2016, 01:29:10 am
content: You don't need to quote every post as it restricts me from making edits for errors, spelling, grammar and such.For the moment I've just gone with a quantity of one percent resistors to get the meter closer to agreement with my other gear and am in the process of sifting through them and measuring each one on a meter that I trust, no doubt that will be amended in the near future but again it's entirely up to you as to how accurate you need to make it, for my usage I don't see the outlay for 6 better quality resistors at around $40 bucks each being warranted at this point in time for this particular meter but that may change or I may decide to purchase another bench meter altogether.

author: h.bashar
author_rank: Contributor
timestamp: August 28, 2016, 02:08:03 am
content: Thanks for the heads up, so basically 0.001% or better? that is a lot of money there in those resistors, I have tried most of the ranges using 0.1% resistors (except for the 1M and 10M using 1%) and all resistors fell within tolerance

author: Vgkid
author_rank: Super Contributor
timestamp: August 28, 2016, 03:34:21 am
content: You should be fine with %0.005 resistors, or someone with a calibrated 6.5 digit dmm. Heck 0.01 resistors should be decent enough.

author: Muttley Snickers
author_rank: Unknown
timestamp: August 28, 2016, 11:49:32 am
content: Quote from: h.bashar on August 28, 2016, 02:08:03 amSorry I wrongly interpreted your previous question about what tolerance of resistors are best suited to verify the meters accuracy and I'm probably not the best person to advise in that regard but it looks like Vgkid had it nicely covered.Also your meter sounds like it's pretty well spot on going by your last post so you may not need to do much in relation to the calibration process at all, have you checked the calibration status by pressing the cal button and then the log key?, and only do this if you are content to verify whether the unit is using true or default values as described in both the manual and the cheat sheet. Do not press the store key whislt the cal button is depressed or you will load the default values if it hasn't already been done.Lastly I posted back at reply #9 the brochure for the Arcwin software if you need it, there might be some handy information on its operation and I did amend the cheat sheet after first posting it so watch out for that as well as it is not finalised as yet.

author: h.bashar
author_rank: Contributor
timestamp: August 28, 2016, 05:47:14 pm
content: Just made a custom cable for the serial comms and I can confirm that the software is fully working under win7. I did check the cal log on the meter and all were set to 1's. finally just a question on theREAD?command, to take a reading I used1 READ?followed byREAD 1and it works but I am not sure if this is the shortest method to capture an instantaneous meter reading