GO7 chassis ressurection EDIT 9: How nit-picky are component values?

[Kevin Mullins]

So are you still lacking AC at the fuse ?
(from the power cord to the fuse holder)

That is correct. No power to the fuse.

OK, so I just have to ask .... did you try with one lead on the fuse and the other lead on either of the AC lines? (if nothing from one did you try the other?)

And you have your meter set to AC and on a setting higher than what should be coming in ... so generally on a 200V setting or so. (not sure what meter you have)

Just want to clarify some basics first. No offense.

[Mauzy]

no. was I supposed to? This is like the first real rebuild and testing project and I never realized how low my DMM skills are.

[Kevin Mullins]

Just want to make sure you aren't trying to take a reading from the same line as the fuse, which would show nothing.

[Mauzy]

gotcha. You worried me there for a second.   

[Kevin Mullins]

Nah, I was just reading through the thread thinking how odd it was not to at least have power at the fuse. So sometimes I like to take a step back and cover the basics.

From the power cord to the fuse is a pretty straight forward circuit, nothing fancy there.

And just to also be clear ... are you talking about the larger fuse or the small fuse?

[Kevin Mullins]

Check for 120V AC here: (see pic)

If no power there then you have a bad power cord, solder joint on the cord inputs, or a bad fuse.
Does yours still have the factory soldered in fuse?

[Kevin Mullins]

Check any large components for bad solder joints such as large resistors and such.

Use your meter to OHM (measure) the resistor in the pic.

[Kevin Mullins]

I believe the fusable resistor FR901 has already been mentioned, but check and measure it as well. (220 Ohm)
Fuse F901 should be measured in DC voltage. From any GROUND point to either end of the fuse.
And continuity check it as well.

[Kevin Mullins]

If you have any doubt on how to use your DMM please read up on it a bit here:
http://forum.arcadecontrols.com/index.php?topic=68787.0

Or post a pic so we can see what you are working with.
I have seen all to many meters fried because it was on the wrong or too low of a setting.

[Mauzy]

No, I put in the new fuse. Came with the kit. Its good. Ive checked that connection several times. I appreciate the pictures. Those will definitely come in handy when I start working on this again.

[Kevin Mullins]

I appreciate the pictures. Those will definitely come in handy when I start working on this again.

No problem .... I just snagged a few from http://www.pinrepair.com/g07/ to use since I don't have a GO7 chassis handy.

Let us know how it goes and what you find out.

[Mauzy]

Ok. Im getting ready to begin working on this baby. One quick question: Will I damage the chassis at all if initial tests are run with no video input? This would make this way easier as I have a tube and matching yoke on my workbench now.



Also, When did this get put here >>> ?

[SirPeale]

Nope, you'll be fine.  But you won't be able to see if anything pops on screen, either.

Make yourself a video test rig!

http://forum.arcadecontrols.com/index.php?topic=80378.0

[Mauzy]

oooh... spiffy. Ill have to look into that.

In the mean time, I tested and I have the proper voltage at the fuse, but I found that the big white 2 ohm brick thing reads as an open load. I assume this is a problem? FR901 checks out all right.

EDIT: Why does that keep happening? I went and tested a ninth time, and this time it read 2 ohm... still nothing going to the tube - no buzz or glow.

[Mauzy]

Ok. So now Im back at the 2 ohm white thing is bad. I looked at my meter and found that it was reading 2 M Ohm, which I'm interpreting as 2 milli-ohm. When I tested the same thing on my known good chassis, it read as 1.1 OHM, no M. According to one of the DMM tutorials, it shows something reading XXXX M ohms, but they say its just ohms. Oy vey.

[Kevin Mullins]

The large resistor should be 2 Ohm .... on the average DMM you have it set on the lowest setting, something like the 200 Ohm range. You may even want to disconnect one end and test it as there may be something in the circuit causing odd measurements.

[Mauzy]

All my DMM has on it is an ohms sign. No adjustment as to the sensitivity. Ill post a pic in a little bit. Ill also try taking it off the board.

[Mauzy]

YEE-FREAKIN-HAW!  I switched out the supposed bad resistor with the good one from the good chassis and IT WORKS!

So what the hell is that thing and where do I buy another? Of course Im talking about the Ceramic resistor type thing at R902

[Ken Layton]

It's a 2 ohm, 7 watt ceramic resistor with "standup" type leads.

Bob Roberts sells a 2.7 ohm, 7 watt "standup" resistor:

http://homearcade.org/BBBB/parts.html#resistors

His will work perfectly fine in your application.

[Mauzy]

Oh so the Ohms can be a little different but the wattage needs to be the same? I'm not sure that I understand resistors other than the fact that they "resist" the flow electricity, causing a lower voltage and such.


Give me a few hours and Ill have a Tube swap thread started... thats my next project...

[Ken Layton]

This one is close enough to work.

[Mauzy]

Hokay. So I had this set all cased up nice in a TV case with tube and such, and had it running with a signal so I could do some final adjustments. The picture is really weak, and with the brightness turned up, it gets brighter but has the "brightness is too high" lines going across. Ill get pics of this later.

What I really want to address though is that in trying to adjust a pot, the metal surround on the chassis shocked the crap out of me! Now, I wouldn't think that any components would be touching it as this would cause some serious problems. I tried grounding it, but that would reset the game. Yes. I said reset the game. I did check all of my connections on the board itself and there is nothing touching the chassis metal that shouldn't be. It isn't any closer to the tube than an original monitor set up would be and there is a some what exposed grounding braid going around the tube. Whats the problem now?

[qrz]

the chassis should be at gnd potential. obviously, it is not ......
an isolation xformer is needed with this monitor chassis.


qrz

[Mauzy]

Got that. Ive blown up a couple of these things not having an Iso. Could the iso be too close to the chassis? Ive got the inputs and outputs all taped up, but its about an inch and a half from the chassis. The outside seems to be coated in something as there's not continuity on the outside, but it may leak somewhere...

[Ken Layton]

You must have a fault with the isolation transformer. This model absolutely must have a properly functioning isolation transformer connected.

[Mauzy]

hmm... its a brand new one from Bob Roberts, but I'll check into that. Ive got one that is known to be good.

EDIT: Ok the chassis no longer shocks me with a different iso. I have wiring issues in the cab though as I can sometimes ground the joystick handle and that will reset the machine, but it only does that 1 out of every 10 or so touches.  who knows. I know the chassis did it a couple times, but theres something else wrong.

Here's what Ive got so far. If you look at the white text, its really blurry. The maze is pretty well focused. Also, this is as bright as I can get without having lines. The other way old, burned tube is brighter and clearer than this and it takes a minute and a half to show a picture...

Let me know if that picture is too big... didn't mean for it to be that big...

[Ken Layton]

The blue gun in the picture tube needs to be "zapped" (it's weak). You'll need a rejuvenator to do this.

[Mauzy]

crap in a hat! Ive spent almost $70 bucks trying to build this thing and it turns out to be a crappy tube... oh well... Ill be on the hunt for a new tube then unless I can find a really cheap rejuvenator.

[Mauzy]

Well, I played with the color drives a bit and I think I have it close enough to use for a while. Now the color looks as good as the old monitor with a little bit more...uh...glow in the black portion I guess you'd say around the colored graphics than the old tube.

EDIT: Spelling...

[qrz]

in the meantime, boosting the filament voltage may help.
if u don't wish to make your own winding  see : http://www.mcmelectronics.com/product/33-595

qrz

[Jess--]

I have seen all to many meters fried because it was on the wrong or too low of a setting.

I was lucky not so long back. put my dmm across 240v mains while it was set on continuity check, all it did was bleep a lot. I guess Avo still build decent meters

[Mauzy]

This one is close enough to work.

What about a 7 watt 1.8 ohm? I was just opening a 25 inch TV for my next project and found one of these in nice condition waiting for me inside.

[Mauzy]

Yea, it works. Well, for the 20 minutes its been on it works...