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).

Cool thanks, I'll give all that a go tonight

 

OK, with the scope calibrated, I think I'm seeing 10v AC when I probe over the two inputs from the transistors on the working board. Does that sound about right?

Edit: ...and I just tried the same thing (measuring for AC voltage between the two lines from the transistors to the transformer) on the dead board and I don't seem to see anything. I've confirmed they're still definitely feeding +6vDC in, but nothing when looking for AC.

Incidentally, the working board uses a D882 and an C2785 as the transistors which are both different than the ones on the dead board but I assume they're doing the same job.

 

On the working board, connect the scope ground to the black wire (black arrow below) and the probe tip to the red arrow. Let us know what you meaure. Also on the working board measure the DC voltage across the points in the green circle.

If you check them on the non-working board I think you will get nothing.

I am confused about the transistors. Can you get clear pictures of the transistors so I can see the package type and say which transistor is which type number - this for both boards.

 

On the working board, connect the scope ground to the black wire (black arrow below) and the probe tip to the red arrow. Let us know what you meaure.

Sorry, I should've been a bit clearer. The working board is similar but not identical. It's from another game by the same manufacturer and has the same basic layout of 2 transistors feeding what we now know to be a transformer but the rest is different enough not to be a good comparison. I do have an identical working board on its way to me though so I'll measure that one when it arrives instead. In the meantime though, if I scope between the ground wire and the equivalent red arrowed pin on the similar board, (I think this is one of the pins that gives -33vDC), it only shows 5vAC which makes me think I'm reading the scope wrong. If this isn't what you expected, forget it for now and we'll pick it up when I have two identical boards to compare!

Also on the working board measure the DC voltage across the points in the green circle.

I'm not certain what the equivalent points on the similar board are for this capacitor so again, I'll wait until the identical board arrives.

I am confused about the transistors. Can you get clear pictures of the transistors so I can see the package type and say which transistor is which type number - this for both boards.

Really sorry for the confusion, hopefully the above helps explain it if you thought both boards were the same. For info, the dead board has a D471 at location S02 and a C945 in location S03 immediately to its right. Here's a snap from the top...


...and some better focused ones from the sides.



I think mentioning the transistors on the similar working board confused things but for full disclosure, it looks to have a D882 and a C2785 feeding the equivalent pins on its transformer so I am assuming they are doing the same job. Both boards show +6vDC going to the transformer from the middle pins of the transistors anyway, with 10vAC on the working and nothing on the dead board.

The dead board was bought as a spares/repair off Ebay and it looks like the previous owner might've already been at it so maybe they tried to fix it and put the wrong transistors in? I'll hopefully be able to clear that theory up when I get a hold of an identical working board later in the week

Ta so far!

 

OK, I'll await developments.

 

At last! The working board has finally arrived and I can do some measuring...

On the working board, connect the scope ground to the black wire (black arrow below) and the probe tip to the red arrow.

I had to mess about with the scope settings to get something visible on-screen for this. I set Time/Div to 1μs, Volts/Div to 2 and had to use a 10:1 attenuating probe. Initially, it measured about 2.5 divisions or thereabouts on-screen which I think given the settings means ~50v? After about 5 minutes of being on though, it expanded to a full 4 divisions which if I'm right makes it now giving 80v. I'm not sure why it changed over time but I've uploaded pictures of both states so you can see the difference for yourself - maybe I've read it all wrong.

Also on the working board measure the DC voltage across the points in the green circle. If you check them on the non-working board I think you will get nothing.

Probing these with my multimeter gave a solid +36.3v DC on the working one at all times, regardless of what the scope was reading over the other two points. And yep, the busted one gives zip.

Oh and to confirm, the transistors on this new board are the same two as the duff one - a D471 at location S02 and a C945 in location S03.

Based on the above, what do you think might be the problem with the duff board?

Ta in advance!

 

Please measure the resistance across the points in the green circle - both ways round and using the resistance ranges and also diode test setting if your meter has one.
Compare these readings between working and duff boards.

 

The plot thickens! No idea at this point what your thoughts are but happy to measure away

Just in case you weren't sure, the points in the green circle are a 22μf 50v capacitor.

Duff board: With the black probe to the negative side of the cap, it started at 6MegOhms but was gradually increasing. Swapping the probes round gives me a stable 134.7kOhms. Diode test gave .6v with the probes swapped (black to positive) and .889v the right way round.

Working board: Pretty much 0 on all counts. One of the diode tests made the a battery symbol appear on the multimeter - not sure why!

Hope some of that makes sense...

 

Working board: Pretty much 0 on all counts.

Does that mean a very high resistance?
If so then the problem is with the things connected to the secondary winding of the transformer - leave the transistors alone!

 

Does that mean a very high resistance?
If so then the problem is with the things connected to the secondary winding of the transformer - leave the transistors alone!

I think it probably means no resistance at all. It's similar to what happens when you simply hold the two probes together except it flickers every now & again a little. This is the same both ways round.

EDIT: sorry, my mistake. The other way around, I get OL and the battery sign coming up. I'll research what that might mean, never seen it before! FYI multimeter is an Extech EX330.

 

I think it probably means no resistance at all. It's similar to what happens when you simply hold the two probes together except it flickers every now & again a little. This is the same both ways round.

Are you SURE you got that the right way round - the working board reads zero ohms?

 

On the bottom of the board there are green patches, for instance running upwards and to the right from the green circle. What are those green patches?

 

Are you SURE you got that the right way round - the working board reads zero ohms?

Yep, this is definitely the working board. Am definitely on Resistance setting, and definitely the same two posts which are a cap.

On the bottom of the board there are green patches, for instance running upwards and to the right from the green circle. What are those green patches?

I've been assuming they're jump points - where a track has to jump a few others.

EDIT: I get continuity at each end of the green patch (by testing from the negative of the cap and the pin on the IC that the patch leads to) so I think it's safe to say these are jump points of some sort.

 

Yep, this is definitely the working board. Am definitely on Resistance setting, and definitely the same two posts which are a cap.

This is weird. Zero ohms there would stop the board working, so it would be the cause of the problem on the duff board - but the working board works despite this.

 

This is weird. Zero ohms there would stop the board working, so it would be the cause of the problem on the duff board - but the working board works despite this.

Yeah weird is right. In case you missed it, I edited above to correct myself a little. It's not the same both ways round, the other way around, I get OL (which I think means overload) and weirdly the battery sign comes up. I've googled the manual for the multimeter but all it says is this symbol is for the battery condition, no mention of it lighting up when measuring anything meaning anything. Does that make any difference?

Sorry if all this is giving you a headache!

 

When you get OL which lead is connected to capacitor negative?
What do get on the duff board with the leads that way round and on the same meter range?
The battery symbol may just mean that you are close to needing a new meter battery.

 

When you get OL which lead is connected to capacitor negative?

OL happens with black probe to cap negative.

I rechecked the other way around (red probe to cap negative - which I said was mostly 0 but flickering a little) and I noticed that when it flickers, it's momentarily jumping to OL. The jump is regular too - roughly once a second.

What do get on the duff board with the leads that way round and on the same meter range?

Tried it four times. From freshly turned on, it was at about 18MegOhms but steadily decreasing at about 1Mohm every 5 seconds. Tried again a short while later and it was sitting at about 9MegOhms but increasing slightly.
Third and fourth times were the same - it started at 6 - 6.5MegOhms and increased slowly but steadily.

I hope some of this makes sense...

 

From freshly turned on

Hang on a minute! All these resistance reading should be with the board switched off...

 

Ah oops... will get retesting!

 

OK so with both boards NOT powered up...

Duff board: Resistance, With black to cap negative, started at 34MOhm decreasing rapidly. Seemed to settle around 9-10MOhm. With red to cap negative, I either saw it stable at 137kOhms at first try or about 6MOhm on second. Not sure why the difference. Leaving it alone for a while returns the 137k at first try. Diode test gave .592v with the probes swapped (black to positive) and .818v the right way round.

Working board: Resistance, With black to cap negative, started at 40MOhm decreasing rapidly. Seemed to settle around 10-12MOhm. With red to cap negative, I either saw it stable at 163kOhms at first try or about 5MOhm on second. Diode test gave .596v with the probes swapped (black to positive) but nothing (or OL to be precise) the right way round.

Overall, I would say the only real difference is the diode test with the probes the right way round.