gorf - always blue background

rchadd

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i have a gorf machine which seems to be working fine except that the background colour is always blue on the attract screen and in every subgame (sometimes it should be black).

This does nto seem to be a monitor issue as the colours of the sprites look fine (although on a blue backgrounds some look wierd) the game itself plays fine.

would any have suggestions on where i should start looking to fix this?

could it be a simple issue of a failed component (resistor/capacitor or ic) somewhere?

which board in the board set i should consider looking at first?

i hope you can help me! :)
 
So the game plays normally through all the levels except for the blue background? Is the background a solid blue? Did it just start doing this or did it just start? Did you change anything right before it started? If you could post a picture or two it may help.

Don't have a suggestion yet, but wanted to get a bit more info.

Cheers!
 
Last edited:
Gorf Blue Screen.....

Howdy - you sent me an e-mail to my website...kewl to see you are on KLOV! Did you verify all your connections? Set B+ on chassis and tweak all monitor adjustments? If so...and no improvement.....I would try two quick things before we get into the details. Plug in another 4600 or G07 (not sure what you have) and see if the screen still displays blue......that way you can rule out 100% it is not a chassis/monitor issue.

After that.....look at the RGB Interface Board Assembly and go after cracked solder joints first......re-flow those and let us know if that changes anything......if not then you need to dive deeper...

Alan
 
I recently posted this on another Gorf thread so I just pasted it here since it applies.
----------------------
It could be a flaky pot on the neckboard, specifically one of the two associated with blue. The black level pot for blue might have failed.

I once had a Gorf monitor that had no red. The monitor worked okay in another machine. On one of the Gorf boards, the final drive transistor (Q7) that controlled red was shorted. After replacing it, the red would not shut off completely so it generated a faint red raster covering the entire screen. In this case, the pull-up resistor (R68, 100R) attached to the same transistor had burned open, likely due to the shorted transistor pulling current through it 100% of the time. Replacing both the transistor and the resistor finally solved it.

I mention this just in case the same sort of pull-up resistor in your machine is going bad and causing the continuous blue raster.
------------------------

Here is an excerpt from my repair log...

• Red missing entirely. Replaced R68 (100 ohm) resistor on game logic board. It was burned open.
• Red is now full on all the time. Traced R-Y signal from R68 to Q7 (now stuck full on) and then back to CPU board to Q7 (Motorola H69 [PNP]). Its case is broken. If it doesn't turn on, red will be full-on all the time.
• Replaced Motorola MPSH69 (PNP RF transistor TO-92) with MPSA06. Result was bad. Red now works but transistor is too slow:
current-gain bandwidth products:
MPSH69: 2000 MHz
MPSA06: 100 MHz
Video is badly smeared on "astro battles" blue screen. Tek scope showed B-Y signal as very square shaped pulses. The R-Y signal was very rounded, obviously the transistor is too slow.
Fairchild 2N5771 not fast enough, only 700 MHz.
Fairchild MPSH81 not fast enough, only 600 MHz.

• Ordered MPSH81 from Newark just to try it anyway.
• Installed new MPSH81 transistor. Had to bend leads to swap B & E (part is BEC, board is EBC).
• New transistor works fine. Red is fixed. No smearing is visible. I would still like to replace it with MPSH69 to because it has the proper pin order.
• Found a source for MPSH69 at: http://www.goldmine-elec-products.com/prodinfo.asp?number=G43211
• Installed MPSH69, works fine.
-----------------------------

The main board set produces two video signals, a B-Y and a R-Y. The little video converter board takes these two signals and outputs the familiar R,G,B. Since my red color was the problem, I probed the R-Y signal first and it was not active so I traced it back into the main boardset. It your case, try scoping the B-Y signal on the converter board at pin 7 of the 12-pin header. If it is active, then the amplifier chip on the converter board may be the problem. If it is not active, the problem is in the board set. Since your problem is blue, it'll be the B-Y signal. That leads all the way back to the "CPU" board transistor Q6 which is driven by chip U15. From there, B-Y goes to the "game" board and through transistor Q8 with associated resistors R70 (2.2k pulls up base to +12V) and R71 (100R pulls up collector to +12V) and R69 (330R pulls emitter down to -5V). From here, B-Y goes to the little converter board. That covers it. I hope this helps you solve your problem.

Bill B.
 
I recently posted this on another Gorf thread so I just pasted it here since it applies.
----------------------
It could be a flaky pot on the neckboard, specifically one of the two associated with blue. The black level pot for blue might have failed.

I once had a Gorf monitor that had no red. The monitor worked okay in another machine. On one of the Gorf boards, the final drive transistor (Q7) that controlled red was shorted. After replacing it, the red would not shut off completely so it generated a faint red raster covering the entire screen. In this case, the pull-up resistor (R68, 100R) attached to the same transistor had burned open, likely due to the shorted transistor pulling current through it 100% of the time. Replacing both the transistor and the resistor finally solved it.

I mention this just in case the same sort of pull-up resistor in your machine is going bad and causing the continuous blue raster.
------------------------

Here is an excerpt from my repair log...

• Red missing entirely. Replaced R68 (100 ohm) resistor on game logic board. It was burned open.
• Red is now full on all the time. Traced R-Y signal from R68 to Q7 (now stuck full on) and then back to CPU board to Q7 (Motorola H69 [PNP]). Its case is broken. If it doesn't turn on, red will be full-on all the time.
• Replaced Motorola MPSH69 (PNP RF transistor TO-92) with MPSA06. Result was bad. Red now works but transistor is too slow:
current-gain bandwidth products:
MPSH69: 2000 MHz
MPSA06: 100 MHz
Video is badly smeared on "astro battles" blue screen. Tek scope showed B-Y signal as very square shaped pulses. The R-Y signal was very rounded, obviously the transistor is too slow.
Fairchild 2N5771 not fast enough, only 700 MHz.
Fairchild MPSH81 not fast enough, only 600 MHz.

• Ordered MPSH81 from Newark just to try it anyway.
• Installed new MPSH81 transistor. Had to bend leads to swap B & E (part is BEC, board is EBC).
• New transistor works fine. Red is fixed. No smearing is visible. I would still like to replace it with MPSH69 to because it has the proper pin order.
• Found a source for MPSH69 at: http://www.goldmine-elec-products.com/prodinfo.asp?number=G43211
• Installed MPSH69, works fine.
-----------------------------

The main board set produces two video signals, a B-Y and a R-Y. The little video converter board takes these two signals and outputs the familiar R,G,B. Since my red color was the problem, I probed the R-Y signal first and it was not active so I traced it back into the main boardset. It your case, try scoping the B-Y signal on the converter board at pin 7 of the 12-pin header. If it is active, then the amplifier chip on the converter board may be the problem. If it is not active, the problem is in the board set. Since your problem is blue, it'll be the B-Y signal. That leads all the way back to the "CPU" board transistor Q6 which is driven by chip U15. From there, B-Y goes to the "game" board and through transistor Q8 with associated resistors R70 (2.2k pulls up base to +12V) and R71 (100R pulls up collector to +12V) and R69 (330R pulls emitter down to -5V). From here, B-Y goes to the little converter board. That covers it. I hope this helps you solve your problem.

Bill B.

Old thread, and seeing similar on my Gorf. But, my Q7 is a 2N4401 not the MPSH69. All three in that area are 4401.
 
Old thread, and seeing similar on my Gorf. But, my Q7 is a 2N4401 not the MPSH69. All three in that area are 4401.

Be aware that there is more than one Q7 in the system. Make sure you are looking at the final stage color signal drivers.

1) 2N4401 is probably too slow GWP, is only 250 MHz, and might smear the image, that is if it wasn't for the next issue...

2) 2N4401 is NPN where original part is PNP so 2N4401 wouldn't work in the location to which I was referring.

Bill B.
 
Glad someone is reading this thread!

The board I have has 2N4401s for what I believe to be the final stage and sync on the Gorf Game Board (has the two long .1" connectors on it)

What board did you replace the MPS-H69 on? That would explain why I still have a red haze....

Thanks
 
Glad someone is reading this thread!

The board I have has 2N4401s for what I believe to be the final stage and sync on the Gorf Game Board (has the two long .1" connectors on it)

What board did you replace the MPS-H69 on? That would explain why I still have a red haze....

Thanks

The 3x 2N4401's are part of the video driver circuit on the game logic board and they are numbered Q6, Q7, and Q8, the same references as used on the other ones that I was referring to on the CPU board. I've posted some marked up schematics and PCB photos to help you locate the relevant components.
http://www.biltronix.com/gorf_video_drivers.html

Bill B.
 
Update:

Got the transisitors and an Arcadeshop adapter.

Replaced Q6, Q7, Q8 and the game looks PERFECT on the bench.

Put the set in the game, hook up the arcadeshop adapter and nuttin. Looks like the PS got blown, so I"m tinking I have a short in the harness somewhere.

Question: Do I take out the fuses on the powerboard, or do they stay in?
 
I'm a bit confused now. You said your game was working fine as it was except for the red haze. You replaced the 3 transistors and fixed it. So what is the Arcadeshop adapter for? Your game was running without it previously wasn't it? Can't you put it back the way it was?


Bill B.
 
Okay, makes more sense now. Nice to have the red haze taken care of. I wasn't aware of the reset pin problem. No need to worry about it at the moment under the circumstances.

So rather than repairing/rebuilding the original voltage regulator board, you opted to install the Arcadeshop switcher supply and adapter, correct?

1) Was that the same setup that was running on the bench?

2) The new problem occurred when you moved it all to the cab?

3) Was the AS PS adapter designed specifically for Gorf? I'm assuming yes.

4) Did you get a hookup drawing or instruction sheet with the Arcadeshop kit? You could email to me and I could take a look at it so I know better what you are dealing with.

I'm assuming that with the AS PS adapter installed that the original regulator board output is not hooked up to anything at all so I doubt that its fuses matter. The original power block in the bottom of the game still has to be there to serve as an isolation transformer to your monitor, assuming it is an original 4600 or something very similar. The switcher supply can run on 115VAC from either before or after the isolation transformer but the monitor must be isolated or bad things will happen.

Bill B.
 
Le'ts see, correct about the power supply.

1. Same setup on the bench, running off of a Jamma set up wtih Reset tied to 5VDC
2. Yes, problem when moving it to game.
3. AS PS is for Gorf and that game (listed on board)
4. Board screws directly on PS and labeled as to where.

Gotcha on the bottom of the panel.

Thanks!
 
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