569
by greg_Archive
ATR #2 in Studio B-Take up reel motor buzzing, and groaning when tape was loaded and under servo control. This problem was intermittent until the reel motors stopped responding altogether, and the machine wouldn't load tape.Maybe related- Control panel leds flickering intermittently.Some notes on the process-Reseated all PWAs (circuit boards in the card cage)- no joySwapped the Reel Servo board with a spare, and the noise went away. Put the old Reel Servo board back and the machine was still quiet. Turned on the machine the next day, loaded some tape, and the buzz came back. Swapped the Reel servo again, and no change. Put the original back in, and now the reel motors are dead. Swapped all the PWAs (audio boards pulled for the time being). Motors still dead. Exercised both the power supply connectors (motor control routs through it, via a relay)Tested that relay.Other observations:Timer display still works, though fades from dark to fully on slower than normal (I think) over a second or two (after the wake up period ends). Capstan tests normally (when Reel Servo PWA pulled).Switched the speeds (have had problem with that circuit in the past).Voltage measurments on the Reel Servo Card- ± 20v is closer to ±27, don t know remember that s normal. It s been a while ± 12v is a little under ±13v. I measure close to ground on the ground side of the reel motors, < 1Ω.Signals from the tension sensors correct and smooth throughout their travel.When I push the tension rollers out to activate the microswitch, and measure TP 3 or 4 on the reel servo, I measure an instant of voltage when I hit stop, otherwise close to 0v at rest.The dead real motors seemed to be a problem with the œSVO , or servo logic signal getting to the power supply and energizing the relay (completes the reel motor active circuit). I reseated the edge connector on the rear of the card cage motherboard where this signal is sent to the PS, and the reels gradually came back to life. There s still a bit of groaning, or buzzing when the tape accelerates in the forward direction. I m trying to trace it down, but now it s so subtle, I can t scope things that might be abnormal. Day 2-Today I showed up to limp reels again. Wiggling around the wire harness seemed to change that back to functioning again. I then manhandled the 4 reel motor molex connectors a bit and heard the machine whine and moan. It seemed I could get the machine to behave or fail based on slight tension on the reel motor cables/connectors. I saw a bit of arcing in one molex housing in the process. I then cleaned and re-tensioned the connectors, and the transport acted normally. Still, some really faint buzzing. Feeling around to see what was mechanically vibrating, I found that one or both of the fuse holders were warm, and gently wiggling their retaining caps caused a change in the buzzing harmonics. After exercising those connections (removing and reinstalling the fuses) all is good and quiet. Going to leave it threaded and stress test it today to see if it s good for real. If all is well, I'm going to replace the molex connectors with fresh ones. Fingers crossed.Also, the flickering leds never appeared again.Later...Reel Motors still groaning, complainin' for a while after power up. Then reels dead, tape won't load.Tension arm led dead, replacedTension photosensor track damaged, replaced (good thing I had a box of spares at home for my old machine. 15 years later, comes in handy). Warm 5v supply cappower supply swapTested all power transistors (deck mounted), cleaned their connections, applied new insulators and heat sink compound.28kHz spikes seen everywhere..I'll elaborate later.This one's going to be down for a while.OK, didn't elaborate, and now forgot some of the details. Basically, the problem was not solved, even with the alternate supply. Because of the heating 5v power supply cap, I figured I'd just rebuild the PSU, since it's been about 20 years. I just ordered the parts kit from ATR Service since they had everything in one place, caps, transistors, high amp diodes, power switch (already replaced), fresh hardware, and some spare fuses (for just in case?). They even go the extra mile of filing the legs of the TO220 transistors so they sit flush with the board, as the originals did (not a lot of space, and they don't get too hot).The old 9200uF cap which was being used for the 5v supply, the one getting warm, measured roughly 100uF. Yep. Now that the rejuvenated PS is in, the machine seems to be ok, but we'll see. I've been tricked before. Going to run it through the motions, check voltages over the next few days.
Greg Norman FG