AHHA/Bridgeport board repair?

Good luck, AHHA is long out of business. I assume you have the AHHA stepper driver box. I think it was called an RG500 IIRC.

I ran a couple AHHA mills for nearly ten years. One was an Excello and another was the series 1 just like yours.

I converted one of the AHHA mills to Mach. Probably still have the wiring instructions (someplace) if you're interested.

There used to be an AHHA user group on Yahoo. A regular there named Bill ? did AHHA repair work. I don't know if the group is still active.

Karl

group still has some activity

The group is still (semi) active. Bill Griffin is the guy you're probably thinking of, but he doesn't do board repairs. Al Goshy was the repair guy, but I don't think anyone knows how to contact him anymore. Problem with the Yahoo group is that Richard, of AHHA, retired to seclusion. He did make some changes to the group to lock out the spammers that were posting a lot of crap. But that requires new members to be approved by the list owner, Richard. He hasn't been heard from in several years, so the groups membership is static.

Mach would be the way to go IMHO. Or simply dump the Ahha driver boards, keeping the power supply, and use Gecko stepper drivers.

Jon

Which of the Series-1 machines -- one in the BOSS-3 to BOSS-6 range (with stepper motors), or one of the later machines with servo motors? They were all Series-1 machines.

If it is the stepper version, *and* if the conversion used the original driver boards -- the most likely failure is one or more of the power transistors on the big heat sink at the back edge of the electronics chassis. IIRC, there are four transistors per axis, so that is twelve total on the heat sink.

And -- the most likely cause of failure is if you are using a rotary converter to drive the spindle motor and the electronics. Unlike many more recent ones, this uses all three phases -- one per axis to derive power for the steppers. The problem is that a rotary converter tends to be unbalanced in output voltage, so one axis gets too much voltage. As I mentioned below, the output transistors are marginal in handling the voltages applied, so this can induce failures.

And -- under normal use with the original computer, it has three magnetic amplifiers (also called saturable reactors) to reduce the voltage to the drivers -- until the stepping speed is high enough to need full voltage. (A stepper just holding position or steeping very slowly will overheat at the higher voltage needed at the higher step rates.) IIRC, it is 50V on the driver transistors when slow or holding, and 80V when fast stepping. Does the AHHA controller switch the voltage of the stepper drivers as designed?

Anyway -- at 80V, you are very close to the limits of the power transistors around which it was designed -- but those were what was available at the time. Today, probably IGFETS or something similar would be a better choice -- but that would require redesigning the amplifier.

I guess that it could be a failure of the driver boards instead, but that is likely to also lead to failures of the output transistors. (Otherwise, I would suggest exchanging two of the boards to see whether that moves the symptoms to a different axis.

Best of luck, DoN.