Repair on Toshiba ARNI motor control board

[mitch.headington]

Hello everyone, very sorry this is my first post but the company i work for has thrown me to the wolves and i'm in desperate need of help.

I should start by saying i don't have a lot of experience with electronics, but i am an industrial electrician here in Australia. Currently trying my best to get up to speed.

Now down to the problem i have. I've been given the job of repairing these Toshiba motor control boards which were made around 1982 and i'm struggling to find replacement components. Most of the IC's i can find bar the few specially made IC's which aren't purchasable, caps and resistors are mostly easy except for one specific cap which is my main problem. It's a capacitor made by Nippon Chemi-Con, which there are 2 of on the board, and its an electrolytic capacitor. According to the original commissioning engineer from Japan, they are a capacitor which has 2 internal polarised electrolytic caps (which apparently will leak like any other electrolytic) but cancel each others polarity out but also have to be mounted one way only. Here's pictures of the two capacitors:

http://imgur.com/a/bF6po

I'm guessing they are a FCX-H series but google brings up nothing what so ever. I've sent an email to Nippon but i doubt i will get a reply.

If anyone knows anything about these caps that would be a massive help.

 

[(*steve*)]

I would be looking on RS and digikey for 200V or higher 4.7uF unpolarised capacitors to see if there's anything suitable available.

However I would also measure the capacitance, leakage, and ESR of these caps to see if they are still ok before I purchased new ones.

It also sounds like you're looking to replace comments rather than actually troubleshoot the problems. I'd go for troubleshooting first.

 

[hevans1944]

Those do not appear to be electrolytic capacitors. The look like tape-wrapped plastic film capacitors. The dark bar on one end refers to the outer foil part of the wrap, which would normally be connected to common. See this web page for information on this type of capacitor.

BTW, these capacitors do not appear to be stressed in any way... in fact the entire circuit board looks pretty clean... why do you think they should be replaced? Is this shotgun maintenance (replace everything in sight)?

 

[mitch.headington]

Thanks for the replies, sorry i should have given more info in my original post.

Currently where i stand is that i am unable to work on the boards. What i have is just one board which is from a large drive panel which has many boards in it. These are the boards that need to be fixed as the other boards are common and easily replaced. Right now i'm just trying to make sure i have access to all the components if required since these boards are quite old and are very critical. They are from a steel manufacturing plant and for these boards to be replaced and entire new drives system needs to be installed which would cost millions. I'm in no way doing a shotgun repair on the boards, though this is what was done by the previous tech. They are a 3 layered board with power and common in the middle. The boards have been treated pretty badly, though they look good in the photos, and i don't want to cause any unrequired stress to the board. I have an ESR meter on order so i can't test them in circuit yet.

I had a guy come over from Japan yesterday, the original commissioning engineer, and he was very specific that they aren't a plastic based cap. He said yes, they look very much like one (that's what i originally thought they were too) but they were actually two caps in one. It's possible they maybe have been made just for this board alone, in which case i will have to try and find a donor board with good parts should it be required.

Also, this is my first foray into electronics so if anyone has any good resources on board repair they know of i would be very appreciative. I should note that i had done a IPC soldering course on rework and repair and i'm confident at that, just not so much fault finding with boards.

Thanks so much guys

Edit:

The reason why i cannot work on the boards is that i need a spare drive panel to access the programs stored on the boards to save them to tape before i can work.

 

[(*steve*)]

A belated welcome to Electronics Point, Mitch.

If this capacitor is unobtainable, I would investigate alternatives. A pair of electrolytic capacitors in series with their polarity reversed essentially is a non-polarised electrolytic. It should not matter which way it is connected in the circuit. You would be advised to try to source a circuit diagram and find out from the engineer what the actual required characteristics of this capacitor are. It is not unlikely that a different type of capacitor could suffice (even if it physically larger). You would need to consider whether there is clearance for a larger component though.

This might be a suitable alternative.

Fault finding is something that is taught by experience. The only thing I can guarantee is that the longer you do it the better you'll get.

 

[hevans1944]

I had a guy come over from Japan yesterday, the original commissioning engineer, and he was very specific that they aren't a plastic based cap. He said yes, they look very much like one (that's what i originally thought they were too) but they were actually two caps in one. It's possible they maybe have been made just for this board alone, in which case i will have to try and find a donor board with good parts should it be required.

So, this "commissioning engineer" from Japan was there in 1982 when the boards were manufactured 34 years ago? And he remembers that these film capacitor "look a likes" are really two back-to-back electrolytic capacitors that happened to be required (in 1982) to create non-polarized 1 μF and 4.7 μF 200 V capacitors way back then? And you think they may have been especially made for this Toshiba controller? Can you ask this engineer to recommend a modern equivalent replacement part, perhaps a low-ESR plastic film capacitor of comparable dimensions, just in case these "went bad" after only three decades in the field? After all, there has been some progress in capacitor manufacturing technology since 1982. And what about those obviously real electrolytic capacitors on the board? They should be near the end of their life after 34 years, although there is no obvious sign of leakage or bulging. Do you have schematics and other documentation for these boards that will be required for troubleshooting?

 

[mitch.headington]

Thanks for the replies.

The commissioning engineer was there in Japan (hes Japanese and works for Toshiba) when the boards were made and was flown to NZ to oversee their install there. He visited me here in Aus yesterday and gave me a run down of the board, how it works and mostly likely the common faults. I MAY be able to get a suitable alternative out of him, but i asked him for the board schematics and he said no, 'toshiba private, cannot give'. He does have schematics for it still i am pretty sure so that might be an option. The problem is that these caps wont be testable by an ESR meter, according to the engineer and the other guy i'm working with, though i cant remember why. I'll put these on towards the bottom of the list in terms of probability to fail for now. I will also ask the engineer if a standard PP cap and be used as a replacement.

The obvious electrolytics that are on the boards (i currently have 3 boards, there are about 200 in service) have been replaced on some of the boards by someone else previously. I've ordered those already as they are available, and will test them with the ESR meter prior to commencing work.

 

[debe]

The green & yellow caps are unlikely to give any trouble, the other electrolytics are more prone to failure. Im pretty sure they are Metalised Polyproplene caps that are available here in Australia from WES components. Heres some pics of some of those caps from an old Decca radar 1970s vintage & still test ok. Since you are in Aus if you are repairing Electronics then WES components is a good place to have an account with.

 

[hevans1944]

Hello everyone, very sorry this is my first post but the company i work for has thrown me to the wolves and i'm in desperate need of help.

I should start by saying i don't have a lot of experience with electronics, but i am an industrial electrician here in Australia. Currently trying my best to get up to speed.

This is a sad situation. From where I am sitting, and reading between the lines, it appears you are being thrown to the wolves. If there are two hundred or so of these boards, there was probably a period of time when they were covered by a Toshiba warranty, and perhaps even a service contract. But no manufacturer can afford to support a product forever. You are fortunate that the "commissioning engineer" was still available to talk with you, but there may be a cultural and a language barrier preventing you from getting the help you need. If Toshiba still considers their thirty-four year old technology to be proprietorial there isn't much you can do about it. Also, your admitted shortcomings in electronics will allow the engineer to tell you anything to discourage you from attempting to maintain these boards. I am sure Toshiba would prefer to sell your company a brand new set of motor controllers. It is likely the original cost (millions of dollars? Really?) was amortized many years ago. That means money should have been set aside for their replacement years ago. The bean counters are just trying to use you to postpone the inevitable. Happens more frequently than you would imagine.

Can't measure ESR because of some "secret sauce" in those capacitors? Horse pucky! See post #8 by @debe.

 

[mitch.headington]

The green & yellow caps are unlikely to give any trouble, the other electrolytics are more prone to failure. Im pretty sure they are Metalised Polyproplene caps that are available here in Australia from WES components. Heres some pics of some of those caps from an old Decca radar 1970s vintage & still test ok. Since you are in Aus if you are repairing Electronics then WES components is a good place to have an account with.

After seeing your yellow NCC cap there i'm more inclined to believe you guys than the engineer who worked on these boards 30 years ago. I'll see if i can get him to double check the board schematics for me if Toshiba aren't willing to hand them over. My ESR meter should be here within a week so i will start testing then.

This is a sad situation. From where I am sitting, and reading between the lines, it appears you are being thrown to the wolves. If there are two hundred or so of these boards, there was probably a period of time when they were covered by a Toshiba warranty, and perhaps even a service contract. But no manufacturer can afford to support a product forever. You are fortunate that the "commissioning engineer" was still available to talk with you, but there may be a cultural and a language barrier preventing you from getting the help you need. If Toshiba still considers their thirty-four year old technology to be proprietorial there isn't much you can do about it. Also, your admitted shortcomings in electronics will allow the engineer to tell you anything to discourage you from attempting to maintain these boards. I am sure Toshiba would prefer to sell your company a brand new set of motor controllers. It is likely the original cost (millions of dollars? Really?) was amortized many years ago. That means money should have been set aside for their replacement years ago. The bean counters are just trying to use you to postpone the inevitable. Happens more frequently than you would imagine.

Can't measure ESR because of some "secret sauce" in those capacitors? Horse pucky! See post #8 by @debe.

Yeah i am lucky that he is still around and still working for Toshiba and available to talk to. It is a bit of a shame that they aren't willing to share their entirely obsolete drawings, maybe i'll see if the boss and wine and dine the engineer and maybe the engineer will accidentally leave a set of drawings laying around somewhere.

You are right that the client should had have planned for this, but it's also possible they really don't have the money for it since these boards aren't from Australia but they are from a country that was severely hit with the GFC. I think my boss and the Toshiba rep are going to go to the client and lay it out to them that this really is a temporary measure.

Thanks again guys.

 

[debe]

Un fortunately the time to get service manuals & circuits are at the point of sale before money changes hands. Had the same problem when purchasing an Auto pilot for my boat, they quickly supplied a workshop manual before money changed hands.