Gossen Metrawatt METRISO 5000A, Insulation Tester 5000V [Success] - Page 1
Forum section: electronics / repair

author: HighVoltage
author_rank: Super Contributor
timestamp: July 14, 2016, 10:25:38 am
content: I have not seen this on on eevblog and thought I will share the repair and upgrade.Gossen Metrawatt METRISO 5000A, Insulation Tester 5000VIt was probably made in the late 90s and seems like new but is not working.Symptom:Not working at all.The 6 x MONO batteries are new.Also Problem:These 10 mm cables are so stiff, when you move cables, the instrument is moving.It is horrible and not really workable.It seems the cables have lost all the softener in the plastic.So, my plan is to exchange these hard and stiff cables with very flexible high voltage silicone cables.I am starting this tread, before I open the instrument.The user manual and datasheets are availableBut I can not find a service manual or the schematicsMay be someone here in the community has seen a service manual?

author: HighVoltage
author_rank: Super Contributor
timestamp: July 14, 2016, 04:42:20 pm
content: Next step, removed the big stiff cables and took the PCB outHere is the back side of the PCB with voltage multiplier and what looks like a high voltage precision divider resistor.Nice to see those red WIMA MKS4 capacitors.There was a time when almost every instrument in Germany had these type of capacitors installed

author: HighVoltage
author_rank: Super Contributor
timestamp: July 14, 2016, 04:44:27 pm
content: Some more pictures of the PCB back side

author: HighVoltage
author_rank: Super Contributor
timestamp: July 14, 2016, 04:51:17 pm
content: Here are some pictures of the front PCBThere are actually two PCB's in this construction and the high voltage is completely separated from the control circuitry.

author: HighVoltage
author_rank: Super Contributor
timestamp: July 14, 2016, 07:04:18 pm
content: It seems I have found the problem.No voltage after the two in parallel input protection diodes.They are marked:S4 77 GIand I can not find a datasheetThey are open in both directions.When I hook up a power supply after the diodes, the instrument seems to work.At least it is turning on.I think these are low dropout germanium diodes?May be 0.2V forward voltage drop?Possible?Any hints from anyone of what I can replace them with?The only purpose seems to be polarity protection, I guess.Any other ideas?Thanks for any feedback.

author: RobK_NL
author_rank: Frequent Contributor
timestamp: July 14, 2016, 07:42:59 pm
content: Damn, that thing is pornographic!The diodes are SS14 Schottky's.http://www.digikey.nl/product-search/en/discrete-semiconductor-products/diodes-rectifiers-single/1376383?k=ss14

author: olliisit
author_rank: Newbie
timestamp: July 14, 2016, 07:58:33 pm
content: Depend on Package Size:S4 = SS14 or SS24 or SS34General Semic. / VishayShotkky Barrier Rectifier

author: HighVoltage
author_rank: Super Contributor
timestamp: July 14, 2016, 09:24:40 pm
content: Thank you guys, that was very helpful.I will see what I can get locally for now and then add the correct diodes later.

author: HighVoltage
author_rank: Super Contributor
timestamp: July 15, 2016, 09:08:29 am
content: OK, I installed some new diodes and the instrument is workingI have no idea why they broke.I did suspect some shortage in one of the tantalum capacitors but that was not the caseNow I want to modify the cables

author: HighVoltage
author_rank: Super Contributor
timestamp: July 15, 2016, 09:30:18 am
content: I looked around for some good high voltage probe tips but I could not find any.Maybe someone here has some suggestions.So, I decided to use the old handle and remove the cable.The original handle is molded around the cable and the 4 mm banana plug.I started with a 3 mm drill bit and then went up to 7.0 mmIt really turned out much better than expected.On the MINUS side, the shielding and 4 inner connectors are connected in parallel to the instrumentBut on the PLUS side, the shielding is connected to a spark gap on the tip and with a 47 kOhm resistor to the ground plane of the PCB.I don't care about the functioning of the spark gap.

author: HighVoltage
author_rank: Super Contributor
timestamp: July 15, 2016, 09:37:37 am
content: Then I inserted the 7 mm silicone cable in to the handleAs a new 4 mm Banana plug I use a MC part and made the tip pointyAdded a small plastic sleeveAnd pressed the assembly in to the handle with a small press

author: HighVoltage
author_rank: Super Contributor
timestamp: July 15, 2016, 09:45:51 am
content: Next, hooked up the cables to the inside of the instrumentSince these are 7mm cables, and the old one had 10 mm diameter, I added a silicone tubing at the outlet.And the PLUS cable got a red piece of shrink tubing for quicker polarity identification.

author: HighVoltage
author_rank: Super Contributor
timestamp: July 15, 2016, 10:03:48 am
content: Fully assemble and working.The spark is jumping good and stable at the 5000 V settingNext is to test the voltage output in the different settings.Hopefully all settings are correct, since I do not have a service manual with calibration instructions.

author: HighVoltage
author_rank: Super Contributor
timestamp: July 15, 2016, 10:25:57 am
content: Testing 100V, 250V, 500VThe 34461A is going to "overload" at 1000V settingHmm, should the Agilent meter not at least show like 5% above 1000 VDC like the 34401A?

author: HighVoltage
author_rank: Super Contributor
timestamp: July 15, 2016, 10:30:30 am
content: 1000 V setting, measured with a 34401A

author: HighVoltage
author_rank: Super Contributor
timestamp: July 15, 2016, 10:35:24 am
content: And the last test,5000V with a 1000:1 high voltage probeReading about 3% highAll perfectly working and I am very happy with this upgrade.Anyone interested in one of these testers, I can only highly recommend them.

author: RobK_NL
author_rank: Frequent Contributor
timestamp: July 15, 2016, 12:17:03 pm
content: Wow, congratulations on a fine job. That looks excellent!Quote from: HighVoltage on July 15, 2016, 10:35:24 amI'll second that. I have the 'little brother'; the 1000D (for digital) and have always found it to be a very good instrument.

author: elimenohpee
author_rank: Contributor
timestamp: July 15, 2016, 02:42:29 pm
content: Very impressive! The modified cables look really clean and professional.

author: Vgkid
author_rank: Super Contributor
timestamp: July 15, 2016, 05:20:49 pm
content: Nice job, the green cables really stand out.

author: BFX
author_rank: Frequent Contributor
timestamp: July 15, 2016, 06:58:54 pm
content: Very nice modification of probes

author: carl_lab
author_rank: Frequent Contributor
timestamp: January 24, 2017, 08:13:45 am
content: You replaced the 2 schottky diodes by non-schottky BYV96?

author: HighVoltage
author_rank: Super Contributor
timestamp: January 24, 2017, 03:41:46 pm
content: Quote from: carl_lab on January 24, 2017, 08:13:45 amThat was for testing purpose only and it worked.A few days later I installed new Schottky SMD diodes.I bought a second Metriso 5000A very cheap on ebay Germany and it had the same problem.Now I have two fully functioning 5000V insulation tester.

author: MarkoET
author_rank: Newbie
timestamp: December 02, 2020, 10:06:19 pm
content: I recently bought cheap Metriso 5000A at unknown condition. Normally, I would first check the instrument, but this time seller was from different city and I am short on time, so I decided to gamble with this... And was losing at the beginning.At first, Metriso acted very strange. At voltage switch position at "OFF,V" it gave 100Vdc output. Also it gave 100Vdc output at other switch position (from 100V to 1000V). At higher positions (up to 5000V) it gave no life, like it is in OFF position. So i searched at internet (not much info), came across this thread, read what HighVoltage was experiencing and decided to open the Metriso.Long story short, I found inside instrument that voltage switch position on PCB was at some strange position. I needed to "calibrate" it myself. So I used the picture provided by HighVoltage here in thread it determinate what is the "OFF, V" position, since you cannot guess it blindly, because rotatory switch on the outside of the instrument must be inline with the circle "switch" on the PCB inside of the instrument. So, after all clicked, I put instrument back together and put it to the tested.And it worked. At "OFF,V" it was off, at 100V switch position, it gave about 110Vdc output, at 250V pos gave about 260Vdc output, and so on. I managed to measure at 1500V switch (1591Vdc output), but for higher voltage I cannot measure the output, but I assume that it is now ok.

author: MarkoET
author_rank: Newbie
timestamp: December 02, 2020, 10:17:22 pm
content: But, still it is now working fully. Even it worked at the beginning, the analog needle is now stuck.If I tap on it, it moved less than mm at the direction that it is supposed to move (left, if it's probes are short-circuted and right at other case). But, it should move like this:So have to figure out now what to do. I did notice that little zero correction regulation is not working anymore (it does not move the needle), so it might have impact on needle being stuck.Any ideas about stuck analog needle? I mean, not fully stuck, it still moves "inch by inch" if I keep taping on instrument, but it must work normally.

author: Gyro
author_rank: Super Contributor
timestamp: December 02, 2020, 10:31:50 pm
content: The Gossen is an insulation tester for electrical installations. It will always output more than the indicated voltage to guarantee that it tests the installation with a terminal voltage ofat leastthe indicated voltage at its maximum specified leakage current (1mA according to BS7671 in the UK).The voltage will (should) always read high to ensure that this worst case requirement is met.Edit: Regarding the meter sticking, it sounds like mechanical impact damage especially if the zero adjust has stopped working at the same time. Check for jumped turns on the hair springs or debris in the magnetic gap around the moving coil. This is a delicate job.

author: HighVoltage
author_rank: Super Contributor
timestamp: December 03, 2020, 07:57:38 am
content: Great that you got it working.You can take the needle meter apart and carefully clean and adjust it.I had one that needed the needle bent a little and then it worked because the needle touched the scale.How are the cables on yours?Are they still soft or as hard as on my above unit?

author: MarkoET
author_rank: Newbie
timestamp: December 03, 2020, 08:42:29 am
content: Thanks for advice, I will certainly be careful and try something.Mine cables are surprisingly soft, guess I've been lucky there. Mine came with to banana clip, but no problem, I have large banana clips from other instruments.