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

[Mauzy]

So I bought a set of GO7 chassis on ebay for my Super Pac Man cocktail. They work great, all is good. The working set came with a dead set with a note: "missing horizontal width coil, plugged in without isolation transformer". Ok cool. Of course it will need the width coil and prolly a cap kit (they look original), but what gets taken out if plugged in without an iso transformer? I did plug them in with a iso and nothing happened.

Also, I have an old low impedance TV tube. I measured the working GO7 and found that it has a high impedance tube. If I can get the dead chassis working and figure out a way to make the tube High impedance, could I Frankenstein a working monitor with a GO7 chassis and TV tube? How could I rig the low impedance to make it a high impedance tube? I still want to fix the dead chassis for a spare, but if I could make another monitor that would be nice too. 

[Mauzy]

Did a little research, found that diodes will be ruined. Pulled one and it has T87A_2-E written on it, but I can't find such a thing on the internet. What are these really called or where do I find them?

[Ken Layton]

The power supply section will probably have some blown (shorted) diodes. The service manual will have a parts list with the diode number listed that you can cross reference a replacement from.

[Mauzy]

I guess my google skills have gone to hell because I can't find ANYTHING pertaining to an RM2-(C) diode. I know its a signal diode, but what am I missing?

[Mauzy]

Are these diodes something common that I would be able to find at, say, Radio Shack? Just gotta know what Im looking for.

[Ken Layton]

What diode number location is it on the circuit board?

[qrz]

if in the pwr sup, then likely 200piv/1a diodes   although , i'd go 400piv/ 2a ..... just a bit more robust 

fyi, ecg/nte125 are general purpose  rated 1000piv/2.5a

i prefer the 400piv rating as the diode may short on a surge , opening the line fuse protecting the circuitry.
a 1000piv  rating may pass a surge voltage and possibly cause circuit damage
( just my 2 cent opinion    )


qrz

[Mauzy]

What diode number location is it on the circuit board?

I was going by the Pinrepair.com G07 section which says in the case of chassis plugged without iso transformer D901 to D904 will be shorted. More damage from there can occur, but it sounds like these will definitely go out.

if in the pwr sup, then likely 200piv/1a diodes   although , i'd go 400piv/ 2a ..... just a bit more robust 

fyi, ecg/nte125 are general purpose  rated 1000piv/2.5a

i prefer the 400piv rating as the diode may short on a surge , opening the line fuse protecting the circuitry.
a 1000piv  rating may pass a surge voltage and possibly cause circuit damage
( just my 2 cent opinion   )


qrz

So it doesn't have to be an exact match?

EDIT: something with these specs? (1N4004)
    * Peak Reverse Voltage: 400V (Max)
    * DC Blocking Voltage: 400VDC (Max)
    * Forward Rectified Current: 1A
    * Silicon Rectifier
    * Diffused junction
    * Maximum Average Forward Voltage Drop: VF= 0.8 Volts
    * Non-repetitive Peak Surge Current: IFSM= 30 amps for 1 cycle
    * Maximum Reverse Current @ 25 degrees C: IR= 10uA

[Mauzy]

So I noticed something rather large today. There seems to be a very large "burn" mark on the board. Its not like a fire burn, but It looks like soot left from a component that smoked. The red circle depicts that area. The Diodes that I have questioned are in the green circle.



What in the red area would be a common suspect for burning? Is this set of chassis even worth bringing back to life considering I will have to cap it AND buy a horizontal width coil?

Wow my workbench looks disgusting in that picture...

[qrz]

diodes in the green circle are general purpose rectifiers   
 a 1n4004 may work ok, or a bit heavier on current with a 1n5404 ( 400piv/3a)

the red circle encompasses the vertical output stage.
this area does get quite warm , as the pcb indicates .
all 'lytics in this area should be replaced at some point ,
and dress them away from the heatsinks ....

qrz

[Mauzy]

and dress them away from the heatsinks ....

Eh? I don't have my degree in electrical engineering yet. You guys have to explain your jargon to my uneducated mind 

[qrz]

keep working on the degree ! 

don't push the cap full into the pcb . leave enough room to allow the caps to be bent away  ( within reason) from heatsinks and 1 watt or higher resistors .

 heat is an enemy of 'lytic caps   

qrz

[Mauzy]

Heh. Ive got a few years left but I plan on getting through it.

So I replaced the diodes with 1N5404s and I transplanted the horiz width coil from a known working set to give it a test. Plugged it in, checked fuse and such and...


nothing. It has a little over 130 volts (dunno why thats so high, but the other G07 has run fine off of it for a year) of isolated electrical goodness goin to it but nothing. No neck glow, no start up sound, no burning smell (guess thats a positive).

Could bad caps cause it to not start at all? I would think that I could at least get it to glow with a screwy picture. What should I be looking for as to bad components?

Also, how can I test the viability of my flyback without killing myself? If I had loads of money I would just shotgun the thing but I'm thirty bucks from broke...

[qrz]

for starters lets check the following :      (use CAUTION -  C904 may be "charged")
f901, fr901 ( 220 ohm/ .5w)  c506 ,c504,c905
and make sure d701,x701 aren't shorted/leaky  ( xrp shutdown )
check c511 .

note: B+ will be high if the h out is not operating ....

[MonMotha]

In your picture above, there appear to only be 3 diodes with an unpopulated spot for a 4th.  If you don't have that 4th, that could certainly cause something like this as you'd be missing a chunk of the bridge.

[Mauzy]

In your picture above, there appear to only be 3 diodes with an unpopulated spot for a 4th.  If you don't have that 4th, that could certainly cause something like this as you'd be missing a chunk of the bridge.

Nice catch. I should have noted that I had removed a diode to get the numbers off of it before I took that picture. I did replace all 4 before testing.

[Ken Layton]

Perhaps this link will help:

http://www.pinrepair.com/g07/

[Mauzy]

What diode number location is it on the circuit board?

I was going by the Pinrepair.com G07 section which says in the case of chassis plugged without iso transformer D901 to D904 will be shorted. More damage from there can occur, but it sounds like these will definitely go out.

Perhaps this link will help:

http://www.pinrepair.com/g07/

Great minds, eh?

[Mauzy]

for starters lets check the following :      (use CAUTION -  C904 may be "charged")
f901, fr901 ( 220 ohm/ .5w)  c506 ,c504,c905
and make sure d701,x701 aren't shorted/leaky  ( xrp shutdown )
check c511 .

note: B+ will be high if the h out is not operating ....

f901 - good
fr901 (r901??) - measured 6.5 ohms??
c506 - couldnt find it...
c504 - good
c905 sad to say i dont know how to test caps without a cap tester, but it topped out at 17.8 ohms and it is intact and not shorted
d701 - good (maybe?)
x701 - not shorted
c511 - intact

Interestingly enough, according to pinrepair, my  h out xistor is toast. go figure. My flyback does have a little melted spot on the outside (looks like soldering iron shape though) and isn't cracked, but the h-out is dead. Can something other than the flyback melting do this?


Heh. look at that. post 400. woo!

[Mauzy]

Seems to me R901 is tied to the deguass feature of the monitor, so i must be looking at the wrong thing, but I still can't find fr901.

I'm putting this project on hiatus for the weekend. Gotta save money for community garage sales....

If i still have money Monday, Ill order a cap kit and HOT.

EDIT: Now, according to pinrepair, both the working and nonworking sets have bad HOUTs, so I don't know what the hell is going on. Also looks like I'll be buying Bob Robert's kit. Comes with H-OUT, the other big transistor, width coil, cap kit, and flyback for less than $40. Sounds like a steal to me...

[Ken Layton]

Yes, the Bob Roberts deluxe G07 repair/rebuild kit should put this chassis back into operation.

BTW, the burnt/dark area of the circuit board is normal. The metal heatsinks generate alot of heat which discolors the board. The sticky splooge covering that area is from some of the wax in the yoke dripping down onto the board, but generally it's from tiny pinholes in the flyback spraying out coolant. That means the flyback is just about to explode soon so replacing the flyback is a priority now. That crap can be cleaned from the board with lighter fluid and 99% isopropyl rubbing alcohol.

[Mauzy]

Yes, the Bob Roberts deluxe G07 repair/rebuild kit should put this chassis back into operation.

BTW, the burnt/dark area of the circuit board is normal. The metal heatsinks generate alot of heat which discolors the board. The sticky splooge covering that area is from some of the wax in the yoke dripping down onto the board, but generally it's from tiny pinholes in the flyback spraying out coolant. That means the flyback is just about to explode soon so replacing the flyback is a priority now. That crap can be cleaned from the board with lighter fluid and 99% isopropyl rubbing alcohol.

Cool. Thats what I figured. I'll also be ordering a G07 yoke from him. I will hopefully be able to fashion a new monitor out of an extra tube I have laying around. Ill hopefully get paid for a computer repair late this week.

[RayB]

"fr901" = Fusible Resistor. Should be the grey ceramic rectangular shaped part, if my memory serves right.

[Mauzy]

"fr901" = Fusible Resistor. Should be the grey ceramic rectangular shaped part, if my memory serves right.

Oh! Makes sense considering I couldn't find that on the PCB. Thanks!

[Mauzy]

So I got everything from Bob Roberts (he even sent Halloween candy!  ) so now Im wondering, do I install everything I got new? Obviously I'll do the cap kit, but should I go ahead with the flyback, HOUT, and the other transistor thats name escapes me at the moment before testing with the new cap kit?

[Mauzy]

I replaced the caps, HOT, and flyback and still have no neck glow, no starting buzz, no burning smell, no caps popping, nothing. 

NOW WHAT?

[SirPeale]

Did you check the fuses?

[Mauzy]

Yup. The cap kit came with new ones and they both check out.

[Tenn_pin]

Do you have voltage anywhere on the boards?

R

[Mauzy]

I was just getting ready to ask for some benchmark voltages on various components on the board. Ill go start poking around. If I dont show up by tomorrow, I poked one too many.

EDIT: Im gonna work on this more tomorrow, but I think I have some really ---smurfy--- joints on the AC in. I wasn't getting ANYTHING at either of the fuses and it even kicked on for a second whilst measuring the AC on the board. I discharged shortly after I heard it energize (can't say energize without thinking Star Trek anymore. What a nerd...) and actually got a pretty good spark on the screw driver. The solder is so thick on the connector I will have to heat it up for a relatively long time. I probably better do my English homework instead. Chapter two of The Great Gatsby is due tomorrow...

EDIT again: Just completely unsoldered and resoldered the AC, no change.

[SirPeale]

If you heard it power up while poking around, you probably still have a bad solder joint.  Take your iron and start hitting every joint on the board.

[Mauzy]

Alright. I'll do that tonight after school. Who needs a social life anyway...


  Like I would have one to begin with...

[Ken Layton]

And remember that the horizontal output transistor and the B+ regulator transistor need to have an insulator between them and the metal frame.

What is the B+ voltage reading on each end of the largest white ceramic resistor to ground?

[Mauzy]

Heres a bonehead question for all y'alls: am I supposed to be measuring AC or DC on board? This just doesn't make any sense to me that it can be completely dead everywhere on board while having the proper voltage supplied to the chassis.

What is the B+ voltage reading on each end of the largest white ceramic resistor to ground?

Is that the one mounted on the side of the metal surround of the chassis? If so, absolutely nothing!

[Ken Layton]

B+ voltage is DC volts. Black meter lead to ground. Red meter lead to the resistor.

Measuring the DC voltage from that giant white resistor bolted to the side frame, one side should be 120 volts DC and the other side should be higher like about 136 volts.

[Mauzy]

B+ voltage is DC volts. Black meter lead to ground. Red meter lead to the resistor.

Measuring the DC voltage from that giant white resistor bolted to the side frame, one side should be 120 volts DC and the other side should be higher like about 136 volts.

Nothing. I'm gonna overhaul the AC in in a few minutes. Depending on where on the connector on the board I test, I get anything from 10 volts to 135 volts.

EDIT: Overhauled the AC in. No change.

[Ken Layton]

Are the batteries in your meter fresh?

[Mauzy]

Yeah. Just replaced them last week. $12 in batteries for that thing!

[Kevin Mullins]

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

Have you measured for AC from the power cord to the diodes in the rectifier circuit? (the four diodes)

Out on a limb:
Check the B+ potentiometer. (note where it's setting is first and be sure to set it back before turning on)
I had a Nanao do something similar and all it was was the B+ pot was bad.

[Mauzy]

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.

What should I be getting at the diodes?


At any rate, this project is on hold for the weekend. I really appreciate all the help you guys have given thus far.

[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...