Author Topic: GO7 chassis ressurection EDIT 9: How nit-picky are component values? (Read 11783 times)

Mauzy · « **on:** October 01, 2008, 07:22:08 pm »

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 · « **Reply #1 on:** October 01, 2008, 10:20:26 pm »

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 · « **Reply #2 on:** October 01, 2008, 11:02:09 pm »

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 · « **Reply #3 on:** October 02, 2008, 06:19:47 pm »

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 · « **Reply #4 on:** October 03, 2008, 04:28:44 pm »

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 · « **Reply #5 on:** October 03, 2008, 05:47:24 pm »

What diode number location is it on the circuit board?

qrz · « **Reply #6 on:** October 03, 2008, 06:35:05 pm »

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 · « **Reply #7 on:** October 03, 2008, 06:46:08 pm »

Quote from: Ken Layton on October 03, 2008, 05:47:24 pm

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.

Quote from: qrz on October 03, 2008, 06:35:05 pm

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 · « **Reply #8 on:** October 05, 2008, 09:55:45 pm »

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 · « **Reply #9 on:** October 05, 2008, 10:19:51 pm »

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 · « **Reply #10 on:** October 05, 2008, 10:27:25 pm »

Quote from: qrz on October 05, 2008, 10:19:51 pm

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 · « **Reply #11 on:** October 06, 2008, 05:39:40 pm »

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 · « **Reply #12 on:** October 06, 2008, 06:58:45 pm »

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 · « **Reply #13 on:** October 06, 2008, 11:10:16 pm »

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 · « **Reply #14 on:** October 07, 2008, 12:10:38 am »

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 · « **Reply #15 on:** October 07, 2008, 09:11:07 am »

Quote from: MonMotha on October 07, 2008, 12:10:38 am

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 · « **Reply #16 on:** October 07, 2008, 12:42:41 pm »

Perhaps this link will help:

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

Mauzy · « **Reply #17 on:** October 07, 2008, 05:33:17 pm »

Quote from: Mauzy on October 03, 2008, 06:46:08 pm

Quote from: Ken Layton on October 03, 2008, 05:47:24 pm
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.

Quote from: Ken Layton on October 07, 2008, 12:42:41 pm

Perhaps this link will help:

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

Great minds, eh?

Mauzy · « **Reply #18 on:** October 07, 2008, 11:16:35 pm »

Quote from: qrz on October 06, 2008, 11:10:16 pm

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 · « **Reply #19 on:** October 09, 2008, 09:14:34 am »

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 · « **Reply #20 on:** October 13, 2008, 11:51:12 am »

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 · « **Reply #21 on:** October 13, 2008, 08:06:46 pm »

Quote from: Ken Layton on October 13, 2008, 11:51:12 am

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 · « **Reply #22 on:** October 15, 2008, 12:36:38 am »

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

Mauzy · « **Reply #23 on:** October 15, 2008, 05:33:31 pm »

Quote from: RayB on October 15, 2008, 12:36:38 am

"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 · « **Reply #24 on:** October 27, 2008, 05:05:17 pm »

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 · « **Reply #25 on:** October 27, 2008, 07:43:08 pm »

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 · « **Reply #26 on:** October 27, 2008, 08:03:49 pm »

Did you check the fuses?

Mauzy · « **Reply #27 on:** October 27, 2008, 08:29:53 pm »

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

Tenn_pin · « **Reply #28 on:** October 27, 2008, 08:55:16 pm »

Do you have voltage anywhere on the boards?

R

Mauzy · « **Reply #29 on:** October 27, 2008, 09:35:46 pm »

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 · « **Reply #30 on:** October 28, 2008, 07:04:41 am »

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 · « **Reply #31 on:** October 28, 2008, 10:00:19 am »

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

Like I would have one to begin with...

Ken Layton · « **Reply #32 on:** October 28, 2008, 12:59:04 pm »

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 · « **Reply #33 on:** October 28, 2008, 05:50:12 pm »

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.

Quote from: Ken Layton on October 28, 2008, 12:59:04 pm

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 · « **Reply #34 on:** October 28, 2008, 06:33:20 pm »

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 · « **Reply #35 on:** October 28, 2008, 07:09:02 pm »

Quote from: Ken Layton on October 28, 2008, 06:33:20 pm

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 · « **Reply #36 on:** October 28, 2008, 08:08:56 pm »

Are the batteries in your meter fresh?

Mauzy · « **Reply #37 on:** October 28, 2008, 08:11:54 pm »

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

Kevin Mullins · « **Reply #38 on:** October 28, 2008, 09:49:06 pm »

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 · « **Reply #39 on:** October 28, 2008, 10:29:01 pm »

Quote from: Kevin Mullins on October 28, 2008, 09:49:06 pm

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.


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