Need help identifying an old 80's component...

Thread Starter

StirlingSteve

Joined Jan 13, 2020
29
Hi there,

I'm trying to fix an old electronic game and there's one component I don't recognise on the board, although I suspect it's some sort of step-up converter. It has 10 pins and I can see +6v going into two of them but nothing coming out of any others. I have another game that works and it has a very similar (but not identical) component which is putting out -33v on 5 pins, hence my assumption of its purpose. It has "TX-90 4 5 TDK" written on it and can be seen in-situ at the bottom of this photo:

IMG_20200215_1921068.jpg

Can anyone tell me what this is, whether it's likely to be broken if there's +6v going but nothing coming out and if so, where on earth would I find a replacement?

Cheers in advance to all you clever electronics people who know exactly what it is and where to find one!
 

jpanhalt

Joined Jan 18, 2008
8,717
My eyes are very old and blurred. The only 10-pin component seems to be labeled 68kΩ. That makes it a resistor array. The fact that the label on the board seems to be, " RO1" may be consistent with that. Maybe, it is some sort of resistor, not a "micro."
 

hexreader

Joined Apr 16, 2011
391
My guess is transformer. A side view might lead to a better guess.

What component designation is written next to it? Is it T01?

If it is a transformer, then more likely that a transistor (S02 or S03) driving it is blown, rather than the transformer itself.

Can you trace all of the wires and produce a schematic?
 

paulktreg

Joined Jun 2, 2008
781
I'm sure the OP is referring to the circular component bottom right marked TX-90.

I've had a look and can't find any information.

Could be an inductor or transformer?

Picture of the copper side of the board may help.
 

Thread Starter

StirlingSteve

Joined Jan 13, 2020
29
I'm sure the OP is referring to the circular component bottom right marked TX-90.

I've had a look and can't find any information.

Could be an inductor or transformer?

Picture of the copper side of the board may help.
Hi Paul - yes you're right, I don't mean the IC or the resistor array, I am indeed referring to the circular component at the bottom.

To answer hexreader's question, it's labeled I01 which I assume would tally with your idea of it being an inductor then? I'm sorry, I'm a total novice when it comes to electronics, I have no training and am completely in the dark as to what an inductor is but I'll go off and google it :)

If it is an inductor though, what might the markings mean? I know the TDK part is probably the manufacturer but the other bits would be a mystery to me.

If it'll still help, I'll upload a picture of the back but I think you might have hit the nail on the head with your inductor idea.

Ta!
 

jpanhalt

Joined Jan 18, 2008
8,717
Maybe that also has 10 pins. Why not wait for the TS to circle the component in question.

Edit: Thank you for the pellucid question. Does that device have 10 pins?
 

Thread Starter

StirlingSteve

Joined Jan 13, 2020
29
What is the component designator?
View attachment 199714
TX makes me think it's a transformer.
Thanks Dennis, it's I01 so from what hexreader says, maybe an inductor?

Maybe that also has 10 pins. Why not wait for the TS to circle the component in question.

Edit: Thank you for the pellucid question. Does that device have 10 pins?
Yep, that is the device I mean and yes it has 10 pins, all arranged in a circle. The arrow points to (I assume) pin 1 - I think it's tied to ground on the board but I might need to buzz it through again to confirm that.

I also just googled what an inductor is and it does look similar to me. Question now is, if I put 6v in should I get -33v out and if not, is the device goosed or is something else?

Edit: Just buzzed it and if we take the arrow as pin 1, it and the next two along the top edge are all pinned to ground. No idea if that helps identify it though...
 

AlbertHall

Joined Jun 4, 2014
9,272
It is unlikely to be a problem with the transformer but with the circuit driving it as already said.
What are the markings on S02 and S03?
Can you check them?
 

Thread Starter

StirlingSteve

Joined Jan 13, 2020
29
It is unlikely to be a problem with the transformer but with the circuit driving it as already said.
What are the markings on S02 and S03?
Can you check them?
Hi there, thanks for helping. S02 is a D471 transistor and S03 is a C945 transistor. Both have been tested out-of-circuit and appear to be OK.

I am a little confused as to what this component is now - I know that a similar working board for a different game has a very similar component and when fired up it has two of its pins getting +6v in on one side (as supplied from an external 6v DC power supply) and it turns into -33v on 5 of the pins on the other side. If inductors or transformers can't convert +6v into -33v then what sort of component could it be? The TDK site wasn't very informative unfortunately but this thing is from 1984 so maybe it's all too old to be listed anymore.

There's very little else on the board, I've tested all the resistors and capacitors already, plus two of the (I think zener) diodes so all that's left to test is the other diodes but I can't identify some of them as they just have single-colour bands so have been concentrating instead on this component. I was really just wanting to know what it was so I could buy a new one and stick it in to see if it makes any difference.

Any further thoughts, anyone?

Ta!
 

Thread Starter

StirlingSteve

Joined Jan 13, 2020
29
Can you trace all of the wires and produce a schematic?
I've never made one before, mainly because I find even trying to read them makes my head hurt! Having said that, the back of the board is pretty simple to trace so I'm sure with some time I could work it all out so I'll give it a go :)

Here's a pic for info. IMG_20200222_2348512.jpg

Oh and FYI, this is the game it's from: Grandstand Star Force VFD console 1984

Thanks all for the help so far!
 

Thread Starter

StirlingSteve

Joined Jan 13, 2020
29
I believe your circuit is similar to the one below. The component in question is a transformer driven by two transistors. The transistors oscillate with the transformer making AC which is 'transformed' to make other voltages which cab then be rectified to make voltage supply rails for the other circuitry.
https://electronics.stackexchange.com/questions/366872/self-oscillating-inverter-questions
Right - wow! Cheers for the detective work Albert, that's brilliant! It does sound very much like what it's doing, how clever! Oh and I guess that would also explain why it's I01 on the board - I for Inverter! Fantastic!

Forgive my total ignorance but if the same setup on another board shows +6v coming in on two rails (as supplied by the PSU) and this one shows the same two +6v inputs fine, would it tally that the transistors feeding the transformer on this board are likely OK and the issue, however unlikely, could be with the transformer itself if it's not giving anything out? Or is that too simplistic an assumption to make? I gather transformers don't generally go wrong.

I guess in other words, I'm asking - if I find one of these transistors to replace it with (and I still don't know how I'm going to find one!) do you think it's likely to be the culprit? I have yet to desolder it for out-of-circuit testing as I wouldn't know how to test it anyway without a pinout to refer to.

Cheers again for the detail though, it's all been very interesting!
 

AlbertHall

Joined Jun 4, 2014
9,272
this one shows the same two +6v inputs fine, would it tally that the transistors feeding the transformer on this board are likely OK and the issue, however unlikely,
You are only measuring DC. The transistors need to make AC for the transformer to work.
You might try measuring AC voltages and comparing between working and non-working boards.
 

Thread Starter

StirlingSteve

Joined Jan 13, 2020
29
You are only measuring DC. The transistors need to make AC for the transformer to work.
You might try measuring AC voltages and comparing between working and non-working boards.
OK, I see (or should that be IC!) ...but even if I was measuring for DC, shouldn't the two boards show roughly the same thing if they were both in a working state?

FYI I measured for AC on all 5 -33vDC pins on the working board and they all fluctuate regularly between 32, 12, 4, 1 and then back to 32 volts in a constant cycle.

I'm clearly a hopeless case without even a basic understanding of electronics and I fear I'm reaching the end of people's patience a bit but if you're still willing to give me some help, can you tell me if I am measuring for AC correctly? To measure DC I had the ground probe of my meter attached to where the negative wire from the PSU connects to the board and the positive probe on the pins in question. Do I use the same approach for AC or am I doing it wrong?
 

AlbertHall

Joined Jun 4, 2014
9,272
Yes. that's right.
You might also measure AC between the two pins which you measured at 6V. That is one lead one of theose pins and the other lead on the other pin.
Multimeter AC ranges are designed for 50/60Hz sine waves so for this measurement they are not good. Do you have (access to) an oscilloscope - they are much better for this kind of measurement.
 

AlbertHall

Joined Jun 4, 2014
9,272
For your oscilloscope, you can get the manual here.
Before switching it on read section 5 of the manual.
Before measuring anything read section 6 and make the first signal you measure the 'Cal' signal (at the bottom right of the CRT display).
 
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