Restore of a nice Donkey Kong - COMPLETE

[melvinbates]

 :applaud:Wow that cab looks beautiful.

[Shortbus]

NICE WORK!

[Maximus]

Encouraging.....

[Maximus]

Man in having a bad monitor day.

Everything was great for about 3 mins then poof the monitor is now blowing the 300ma fuse at the back of the main board

Arghhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh










Poo

[Maximus]

Looks like the HOT may be bad, I tested it this morning out of circuit and I'm getting 0.47 on each leg in diode test mode, apparently it should be more like 4.53. Found an NTE equivalent for the Q902 part which Bob Roberts lists as a 2SD869, so hopefully FRYs has that on the shelf and I can grab one at lunch time along with a few fuses.

[yotsuya]

Looks like the HOT may be bad, I tested it this morning out of circuit and I'm getting 0.47 on each leg in diode test mode, apparently it should be more like 4.53. Found an NTE equivalent for the Q902 part which Bob Roberts lists as a 2SD869, so hopefully FRYs has that on the shelf and I can grab one at lunch time along with a few fuses.

Griff-

Check this out: http://www.therealbobroberts.net/cirbreaker.html

You can get those circuit breakers at Fry's. I went through almost $15 in fuses recently trying to fix a motor control board. Good luck! 

[Maximus]

Oh hell yeah I'm going to grab one of those, thanks man that's a big help. 

[yotsuya]

No prob. I grabbed a 3A one and a pack of those insulated allegator clips to build my own.

[Maximus]

Just came from Fry's and they had everything including the hot and the voltage reg. Got a half amp thermal circuit protector and some insulated clips too.

[Maximus]

We don't need no stinkin' fuses

[Maximus]

Well still no joy. I found that the red lead that goes to the HOT casing is shorted to ground now I'm stuck again. I guess it means something in the circuit is shorted

[Maximus]

OK here we go back into schematic hell. So I am assuming that the red line going to the H.O.T at Q902 is not supposed to be grounded. I'm still scratching my head as to why the monitor worked for about three minutes and then just went poof. So where are my electronical gurus peoples? I wonder if the voltage regulator has taken a poop.

[welash]

It is a little hard to read the schematic, but I think that is Q902 in the box at the bottom of the page.  Do you know if the case is connected to the collector, the base or the emitter?  If it is connected to the base or emitter, both of those would look like a short to ground through an inductor and transformer.  If it is connected to the collector (I think that is more common) then are you sure it is shorted to ground, and it isn't just that you need to let the capacitors connected to the collector charge up.  With a multimeter, if you check continuity across a capacitor, it will initially look like a short, and slowly build up resistance.  Those look like rather large caps, so it might take a while for them to charge up.

[Maximus]

To do the test i was just putting my negative to the chassis and then my positive to the red wire not connected to the HOT and getting a short reading. If you click on the schematic it will go full size.

[welash]

Ok, you made me get out my glasses.

According to the package diagrams on the right side, the case of Q902 should be the collector.  Looking at the values of the capacitors, they seem to be pretty small, (100s or thousands of pico farads) so they should charge up pretty quick.  Makes sense that they wouldn't be too big in a relatively high frequency circuit.  It is still possible that if you have the yoke connected that something on that looks like a short to ground.

[Maximus]

Ok I can test that tonight, I'll disconnect the yolk and try again. If that is the case I'm kind of lost as to how to start troubleshooting this. From all the research I have done so far all the monitor 'experts' seem to be able to say is its a fuse, or the H.O.T. or a bad flyback. The flyback looks fine visually no signs of goo or cracking, the HOT has been replaced. I've got a few PMs and threads out asking on the subject but the silence is now rather deafening.

[g0pkh]

Hi guys

Oh dear... This is turning into a nightmare isn't it.

You have done such great work on the cabinet too.

Ok, I will try to help here too.

You mention this

So I am assuming that the red line going to the H.O.T at Q902 is not supposed to be grounded.

Can you be more specific about where you are testing this.

Looking at the schematic. I can see that the collector of the H.O.T is linked to the top pin of the LOPT (7)

Line OutPut Transformer  (sorry UK terminology may differ from US, I think you refer to it as a Flyback)

Is it this that is short to gnd. if so then remove the H.O.T (or just clear the collector from the print) and check again.

There is another trick of the trade here that I will share, that is that you can test the entire PS and regulator by replacing the H.O.T with a domestic light bulb (60W ish)

across collector - emitter (transistor out of course) Pin 7 of LOPT to Gnd


Another useful bit of test gear LOL 60W domestic bulb soldered to leads with crocodile clips on. Ideas from my TV servicing days.
I should start to charge for all these useful bits of info 

With the bulb connected, it should light and you should be able to measure the correct +B volts across it, the +B should be fully adjustable using the +B pot (VR601)
I can't  see what the +B should be set to, but normally in a monitor such as this, I would expect around 105V to 115V ish.

EDIT
After looking at the capacitor voltages on the +B line I think it will be more like 80 - 90V since caps appear to rated at only 100V

If the line is still short to ground with the Collector of the H.O.T isolated and no lamp connected then I will try to guide you further, we will need to isolate parts of the circuit further

You will need the monitor out now, and on the bench in a usable position (access to both sides of the main board) Don't worry connections to the main board
at this point, it should power up on its own at least to a blank raster.



Pete

[g0pkh]

A word of warning.

be careful when selecting a replacement H.O.T
some have built in diodes across collector - emitter. and some even have a low value resistor across base emitter.

How does your original check out on the meter ?

Pete

[Maximus]

A word of warning.

be careful when selecting a replacement H.O.T
some have built in diodes across collector - emitter. and some even have a low value resistor across base emitter.

How does your original check out on the meter ?

Pete

In diode test mode the old one reads 0.47v between the casing and each leg in one direction and nothing in the other. Someone told me this was bad so I changed it out and then new one reads exactly the same before I even installed it. So that would hint there was nothing wrong in the first place

[Maximus]

Back to the power supply. The parts arrived from Mouser so I installed them all, made sure the resistors and diodes were all back in the board, checked my soldering and fired it up. No smoking R1 resistor, no bangs, no burning, no blown fuses........... no power at any of the pins. 

This combined with my mystery monitor issue, my dead AGM medium res for the Paperboy and some supplier issues for parts are all combining to make my worst week yet in this hobby.

Not a happy puppy.

[g0pkh]

Hmm

Things are not going your way today.

The only way to solve the power supply problem will be to start methodically checking for voltages around the unit now.
You will need to have the supply boards open on the bench out of the metal box and connected to each other. Forget connecting to the rest of the machine at this stage, except for the power input connections.

You need to decide your priorities.

Do you want to sort the monitor out first, or the spare PSU ?

I think you will need time to gather your thoughts first.

Then if you think I will be of further help to you, let me know. Just decide what you want to work on first.

Pete

[Maximus]

Thanks Pete,

To be honest at this point I need to get at least three outstanding projects finished up and out of my garage as we are starting to look for houses again so a move could be on the horizon. So as you said, priorities need to fall into place and mine needs to be get things finished. At this point I think I'm going to buy a refurb monitor chassis, get that thing running, slammed in this cab and out of the way. Paperboy after that and a Barrel of Kong after that, my VPin is gathering dust too so I'm in full overload right now.

I will keep the PSU and 20EZ boards as projects that I can come back to when I have more time as they are teaching me some good fundamentals and this is a subject i want to learn more on. Perhaps I can hit you up further down the line for advice and brainstorming. I really appreciate your help, and even though the problems weren't resolved they have taken me further than I have been before.

[Maximus]

Actually Ken Layton advised me to check the diodes and the mylar capacitors in the horizontal circuit in the vicinity of the flyback for the Sanyo monitor, trying to work out which ones they are from that schematic

[g0pkh]

Where does the red wire go on the HOT? 
To the case or one of the other leads ?

With the HOT still disconnected check across C472 is there a short here ?
what about TP11 +B test point (I think) drawing not to clear. Is there a short here also ?

Did you replace all the caps ? are any bulged at the top ? Maybe one was put in reversed in error (we've all done it)

Pete

[Maximus]

Hi Pete

The red wire goes to the case of the HOT. I'll take a look at those components you mentioned . the only cap I see that wasn't replaced and looks a bit bulgy is a green one on the middle of the board. I'll try and check on this stuff tonight

[Maximus]

Pulled the board again maybe the flyback is bad after all?

[welash]

According to the legend on the schematic, the ones that have an N by the voltage rating are mylar (polypropelene film).  The capacitor that you describe, if it is shaped like a big green "chicklet" is probably a mylar cap.  The only mylar cap that I see near the HOT is C473.  I assume when you installed the capacitor kit, you only replaced the electrolytic caps.  There are a couple of those by the flyback (C471 and C472).  You want to make sure if you did replace them, that they are in in the correct orientation.

The other capacitors are shown as ceramic capacitors.  You might want to check them for shorts, just in case. 

The only Diode that I could see being an issue is D453. 

[Maximus]

Thanks welash. Also I just removed the flyback and powered up the board. It didn't blow a fuse and I got audio.

[Maximus]

Yep C471 and C472 are new and in correct. C473 is indeed a big old chiclet

[welash]

With the flyback out, that eliminates C473, C474, and C475 from being shorted.  You might check C471 and C472 and D453.  You could check if pin 11 of the flyback is shorted to ground, or pin 5? 6? 8?, whatever the center tap on the primary side of the flyback is. 

[yotsuya]

  to you, Griff, for not going the 60-in-1/LCD route yet. 

[Maximus]

With the flyback out, that eliminates C473, C474, and C475 from being shorted.  You might check C471 and C472 and D453.  You could check if pin 11 of the flyback is shorted to ground, or pin 5? 6? 8?, whatever the center tap on the primary side of the flyback is.

 12, 11, 10, 9, 6 and 7 all seem to short to each other. 12 looks to be ground. Nothing shorts to 1,2,4 or 8

[Maximus]

With the flyback out, that eliminates C473, C474, and C475 from being shorted.  You might check C471 and C472 and D453.  You could check if pin 11 of the flyback is shorted to ground, or pin 5? 6? 8?, whatever the center tap on the primary side of the flyback is.

D453 is solid actually reads 0.453v in diode test lol and open in other direction. 471 and 472 are new and in correct don't own a cap tester

[welash]

oops, I think I was unclear.  With the transformer out, do the places where pin 11 or the center tap go on the board show that they are shorted to ground.  I would think that with what you were seeing when the transformer was in the circuit, one of those 2 pins must be shorted to ground. 

You could also just check continuity from the + side of C472 to ground.

Wait, did you say that on the transformer itself, with it out of the circuit, pin 12 shows continuity to pin 7?  I would expect to see pins 7 6 and 11 to show continuity to each other and 12 to show continuity to 9 and 10 (that is if I am reading all of the pin numbers right, basically if the pins are all on the same coil they will show continuity at dc).  I would not expect those sets to show continuity to each other.  If 12 shorts to 7, 12 is grounded according to the schematic, so 7 will be grounded.

[Maximus]

In the pin sockets using the diode test with negative probe in socket 12 ground the only sockets that are not open are 8 and 9 bother give me a reading. 9 gives 0.672v and 8 gives 0.926v.

C472 + pin to ground shows open in diode mode

On the flyback pins. Pin 12 ground shorts to pins 6,7,9 10 & 11

Also 11 shorts to 10,9,6 & 7

[welash]

If the drawing of the flyback in the schematic is correct, I don't think pin 12 should show continuity to pin7.  It is possible that the drawing is inaccurate, and that they do share a winding, but I doubt it.  Hopefully someone who knows for sure will chime in.

[Maximus]

EDIT: here's a close up from another copy of the manual...



Looking in the manual, it seems that pins 6,7 and 11 shouldn't have any continuity with pin 12 unless they do share a winding and the drawing is wrong.

Maybe this is causing my blown fuses and issues?

[g0pkh]

If you are directly measuring the pins on the back of the lopt with it out of circuit
Then pin 12 should only show continuity between 10 and 9 since those 3 pins are a single centre tapped winding.

Likewise 7,6 and 11 are the primary and should show no connection to any other pins. Again measured on the back of the tx with it out of circuit

Pete

Certainly if 6,7 or 11 is short to 12 then that will place a short directly across the +B power rail. And result in blown fuses

[Maximus]

If you are directly measuring the pins on the back of the lopt with it out of circuit
Then pin 12 should only show continuity between 10 and 9 since those 3 pins are a single centre tapped winding.

Likewise 7,6 and 11 are the primary and should show no connection to any other pins. Again measured on the back of the tx with it out of circuit

Pete

yes I am doing exactly that

[g0pkh]

I think we can assume in that case that the transformer has failed