Gorf sound repair

scottz29

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Sound went out on my Gorf a while back. 2A fuse on the power brick was blown. Replaced, still no sound. On the audio amp (I have the stereo amp board), tantalum cap C1 was shorted. I recently replaced it and the sound has returned, but now it's very staticky. The speech is only audible on the lowest volume setting. Potting the volume up almost cuts out the speech completely, just a couple pops and clicks when Gorf is talking. The left volume knob hardly has any effect on the sound.

Are these just bad pots, or could there be something else going on in the amp board? Anybody else had this problem?
 
What else do you see in circuit with that cap? Check those header pins for cold solder and replace the pots if you've got new ones handy.

There isn't too much to that board, hopefully that will clear things up sound-wise.
 
Check the two transistors on that sound amp board....I think they're TIP 31 (maybe, I'm guessing from memory. It could be some other TIP number, but there's two). I'd bet one is bad.

Edward
 
Update: Swapped in a buddy's working amp board. Sounds great. Replaced TIP31 transistors on mine, no change.
I guess it's the pots? Not much else to replace on that board... Anyone know where to get them? They don't seem to be common, and I can't even find them on Bob Robert's pot page.
 
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Check R3 and R6 - 2 ohm 1 watt fusible resistors. They are made to go out.

If they test good then check Q1/Q2 (2n4403) and CR1/2 diodes for shorts/leaks.

Last step, R1/R4 - 330 ohm resistors. I'd doubt it would be both pots going at once.

RJ
 
R3/R6 tested good.

R1/R4 were fried and replaced (but tested good).

Checked Q1/Q2 before and recall them testing good, but will test again later tonight when I get a chance to desolder them.

CR1/CR2 I noticed the schematic calls for a 1N4004, but on my board I have 2 diodes piggybacked on top of each other. Not sure if that's normal, and I don't know what the other diode would be...
 
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Update:

  • Replaced CR1/CR2 with a 1N4007, no change. The diodes that were piggybacked were glass packages. Can be seen in this pic (right below the pot)
    IMG_1748.jpg
  • Tested Q1/Q2 again, and they are fine.
  • Pulled pots and tested, ran through the range of 0-200 ohms just fine.
  • Tested voltages at critical places on the board and got +16v everywhere I was supposed to.
I've pulled, replaced and/or tested amost every part on this board. I mean...there's only 11 parts total, and no love? What gives...

I suppose I could replace Q1/Q2 just for good measure...

To reiterate, I've swapped in a friend's working amp board and it sounded great.

And my symptoms are garbled, staticky audio. Gorf's speech comes across as a staticky "buzzing" sound. Compared to a working board where the volume can be adjusted, the volume pots don't do much, and the sound is much softer. If I pot down to almost zero, Gorf's speech can be heard clearly.
 
Those glass piggybacked diodes are capacitors. It's actually a diode and a capacitor piggybacked. I can't totally make out the number, but it looks like a 0.47uf...or a .047uf cap.

Edward
 
Those glass piggybacked diodes are capacitors. It's actually a diode and a capacitor piggybacked. I can't totally make out the number, but it looks like a 0.47uf...or a .047uf cap.
Edward
So...is it okay that I used a 1N4007 to replace with? Schematic shows a 1N4004.

Also, have you checked/replaced the two TIP31 transistors?
Edward
Replaced both.
 
So...is it okay that I used a 1N4007 to replace with? Schematic shows a 1N4004.

A 1N4007 is a fine replacement for the 1N4004. I don't know how important those caps were....but both my working amp boards have those caps installed. It seems to be factory.

Edward
 
Thanks Ed, I appreciate your help thus far... I've never seen a cap in a glass package, but hey, I'm learning something new every day on here. What kind of cap is that, and which one is the cap? Top or bottom? Strange the schematic doesn't call it out in any way...
 
It's simply a glass encapsulated monolithic cap.

The cap is the one without a colored stripe at one side.
 
Weird that the schematics don't call out a cap value. Figures. Mouser doesn't carry anything specifically categorized as a 'monolithic' cap. However, Googling seems to indicate maybe a multi-layered ceramic cap (MLCC) is the same thing? True?

The cap has "1047" marked on it. Based on the typical nomenclature, this seems to indicate 104pf with 7 0's. Doesn't seem right.

I can measure it with my meter, but if it's bad, that won't matter... given my problem, it seems like these caps might be bad?
 
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OK, I just pulled one of my amps apart....it's a 104Z at 50V....so, you need a .1uf50V ceramic cap. Honestly, any of those $.10 ceramic caps in the Mouser catalog will be fine. Radio Shack (might) stock something you can use. Don't forget, you can always go "up" in voltage.

Edward
 
This ended up being a silly mistake on my part. On the blurry board diagram I had, I mistakenly used 330Kohm resistors instead of 330ohm for R1/R4. Turning the page and looking at the schematic set me straight.

Replaced with the correct values, and now Gorf is crystal clear and deafeningly loud. It actually sounds better than before it broke, so I left some of the other parts on that I unnecessarily replaced...
 
WOOHOO!

Glad you got it fixed :D

There's a certain satisfaction in fixing a game... then there's another level of satisfaction for fixing something that has pissed you off for a long time. :D
 
great post

I just donated so I could post in this thread. I have the same issues and just rebuilt most of my ps with the bob roberts kit. I chose not to do the transistors, but I did all the diodes and caps and checked voltages. All look good. I still dont have sound, so now Im gonna tackle the amp board. I just am new to this and am having trouble with the values on the small diodes and such on the board. I love the info here and have been reading this forum and others for months gathering information. I have had the upright gorf for 8 years and originally the voice and sound worked. Then a few years ago the voice went out and attractions, and now all sound. The game plays great, but no sound. So I decided to start restoring my games to their former glory. Thanks
 
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