K7000 med res issues

88mph

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Hi there,

The monitor in my Paperboy went out the other day--my back was turned, and when I looked back the screen was black. I powered down the machine, checked AC to the monitor (which was good), then pulled the monitor. The fuse on the chassis was blown, and according to some flow charts I found this usually means a bad HOT or (rarely) a bad flyback.

I picked up a new cap kit, flyback, fuse and HOT from Bob Roberts, and installed them. I'm not getting any neck glow, but the fuse is holding. I checked the HOT that I removed, and it is good.

So...shotgunning this thing didn't solve my issue. Any recommendations on what to check next?

Thanks!
 
Diodes 19-22 are fine.

I checked out the B+, and it is at 155V. R96 (the grey one) is getting extremely hot even with a short power cycle. I guess I'll pick up a new regulator and see what that does for me.

Thanks!
 
is it possible to test a Voltage Reg with a multi meter?
 
Yes. Do a diode (beep) test between each leg. You should not get zeroes or a continuous beep between any of them (except for a quick one that stops as a cap charges). If you have any doubt as to your readings, pull it out and check it again.

If it appears good, or replacing it doesn't help, check these parts next:

ZD001
R005
IC001
 
Here's an update..

I replaced the voltage regulator (IC4) with one from Bob Roberts. When I fired up to test, there was a flash of light from the fuse as it immediately blew. So now it looks like I'm back to where I started. That seems kind of strange to me.

I just checked ZD001 (is this D001 on the schematics? couldn't find a ZD..), and R005, per Mod's suggestions. Both are coming up good with the meter. I haven't tried replacing IC1 yet, but can a bad IC1 blow the fuse?

One thing I noticed when looking around is that the 'LIN COIL' has seen better days. The coil appears to be intact, but there is a crack in the base. The two leads on the side go to the coil wire, and the lead on the top (furthest towards the CRT) doesn't appear to be connected to anything.

Thanks to all who have replied for their help.
 
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And to clarify, you're testing this with the black wire from the tube connected to the neckboard, right?

Check that big white resistor on the opposite corner from IC4...
 
Yep, the wire from the tube is connected to the neckboard. I will check out the white resistor this evening when I get home. Thanks Mod.
 
I checked out the resistor 103 (the big, vertically mounted ceramic on the opposite corner from IC4), and I'm getting 2.6 ohms, which is good, according to my schematics.

Also, I did a postmortem on the original IC4, and pins 1, 2, and 4 are all shorted. The HOT I pulled appears to be bad (shorted) too. For kicks, I decided to check the new IC4 and HOT that I just put on the board. BOTH are shorted, just like the originals.

Here is my working theory of what happened. Originally, when the fuse blew on this monitor, I replaced the caps, flyback, and HOT. This created a situation in which the fuse held, but the monitor still wasn't working right--namely because IC4 wasn't regulating. (Testing the B+ at this stage verified this.) What I then did was replace IC4. Upon testing, the fuse immediately blew. I'm guessing that the (old) malfunctioning IC4 caused a situation where my new HOT shorted, and then replacing only IC4 was a bad idea, as it was immediately faced with a shorted HOT, which in turn damaged the new IC4.

So it looks like the third time might be the charm--in this case replacing IC4 and Q11 (HOT) at the same time.
 
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Just a followup (the FINAL followup). After swapping in a new HOT, and voltage regulator (and a new fuse), I powered it up. The fuse went off like a flash bulb, and now both my HOT and voltage regulator are blown. At this point I refuse to feed this thing any more good parts.

This chassis has so many hack jobs, it's no big loss. I'm surprised it lasted this long.
 
You didn't mention anything about the mylar caps in your post. How do C36, C38, C69 look? Are they shorted? If they are, that's what that happened.
 
Thanks Peale,

I just metered caps C36 and C38, and C38 is shorted. It looks like that is the source of the most recent takedown. I couldn't find a C69 on this chassis anywhere. What region is it in? I have schematics, and wasn't able to track it down there either.

Do you see a lot of these chassis hacked/modded up? This one has numerous extra parts soldered onto the wrong side of the board, and several jumper wires (again on the backside) connecting traces that don't seem obviously connected. The funny thing is that this chassis (hacked as it is) ran great for years before dying.
 
It's not hacked. Those are undocumented factory fixes from Wells Gardner themselves. Don't mess with them.

C69 (if it was going to be there) would be in the same area as C36/C38. That means you have an earlier version of the K7000, IIRC.
 
youve got some guts messing with all of that stuff. Monitors scare the bejeezus out of me. I would have sucked it up by now and sent it to Chad at arcadecup. but I dont know the difference between a rectifier and a resistor either so... if you can do it, tell me how it goes as my med res monitor has been flaky as well.
 
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