Reseat the connectors on the sound board. Test. Reseat the ROMs on the sound board. Test. Run the diagnostic test and make sure all sounds are present. If any are missing repair and retest. Depending upon if/when you get the sound back you'll need to address either connectors, ROMs, ROM sockets or solenoid(s) or some combination of the above.

viperrwk

Had the same problem, did some searching and found a post by Todd Scott where he also had this problem and corrected it by replacing the 6821 PIA at IC10 on the sound board. I replace that PIA and boom, heartbeat back to normal.
Oddly enough the first replacement PIA I tried was labeled "no good?" and gave me the exact same distorted heartbeat as the original.

Don't rule out the speaker yet. I worked on a Gorgar that had a similar symptom. All sounds seemed ok except the "thump-thump" had a buzzy sound to it. One of the lead wires was broken and barely making contact. Can't remember if it was at the cone or at the terminal. They can be re-soldered if there is enough extra length.

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