1541 CHIPS VS SYMPTOMS - PCB# 251830 or 251777 with Newtronics Twist-door drive mechanism (1984)
The twist-door Newtronics mechanisms seem to suffer a higher failure rate from an open R/W head than the push-down ALPS ones. I don't know why but I speculate that Newtronics didn't seal the heads well enough and moisture
seeps in and corrodes the wiring. Storing a drive in a humid environment is therefore to be avoided. An open head is not repairable. I usually just swap out the entire mechanism. I did once substitute an ALPS head element into a
Newtronics head assembly just to see if it would work... it did. However, that required the epoxy to be chipped away from both, without breaking them, and shims were needed to raise the height of the new head to match the old.
Notes: UC2, UC3, UB4, and regulators VR1 and VR2 run warm normally and bridge rectifiers CR1 and CR3 can run very hot if drive is being accessed. Otherwise, only CR1 (the 5V source) will get hot.
Newtronics drives (twist type door latch) normally run a bit nosier stepper chatter) than earlier ALPS (push down door) types. That mechanism also suffers a high failure rate (open) of the R/W head!
Partial failure common cause of "FILE NOT FOUND" error. Total failure: when drive powered up, red LED stays on and spindle motor
runs continuously.
Common Fault:
UA1 74LS14 LOGIC
Also check: UB4, UC2, UC4, UC6, UC7, UD3, and UD5
Partial failure common cause of "SEARCHING FOR" and "DEVICE NOT PRESENT" errors. Total failure: drive powers up OK but does not respond to computer... no reset or disk access. One failure can lock up computer until it is reset.
Common Fault:
UB1 7406, 7416, M53206P or 7707 LOGIC
Also check: UC3
When drive powered up, spindle motor runs continuously and red LED flashes about once per second.
Common Fault:
UB2 TMM2016AP-10 16K SRAM
Also check: TMM2116AP-15 or MB8128-15
When drive powered up, red LED flashes 2 or 3 times repeatedly.
Common Fault:
UB3 325302-01 DOS ROM 1
When drive powered up, red LED stays on and spindle motor runs continuously. DOS ROM is a common failure.
Common Fault:
UB4 901229-03 or -05 DOS ROM 2
Also check: UA1, UC2, UC4, UC6, UC7, UD3, and UD5.
When drive powered up or reset, red LED comes on and goes out, but spindle motor does not turn. When LOAD attempted, spindle does not turn, red LED flickers, screen displays "FILE NOT FOUND" and red LED flashes. This IC can cause spindle to run without drive access.
Common Fault:
UC1 325572-01 MOTOR CONTROLLER
When drive powered up, red LED stays on and spindle motor runs continuously.
Common Fault:
UC2 6522 VIA (MOTOR CONTROL INTERFACE)
Also check: UA1, UB4, UC4, UC6, UC7, UD3, and UD5.
Drive powers up and resets normally. When LOAD is attempted, screen may indicate "SEARCHING FOR ...", but no motors run and red LED doesn't light. Computer is locked up until turned off or reset.
Common Fault:
UC3 6522 VIA (SERIAL INTERFACE)
When drive powered up, red LED stays on and spindle motor runs continuously.
Common Fault:
UC4 6502 MPU
Also check: UA1, UB4, UC2, UC6, UC7, UD3, and UD5.
When drive powered up, red LED stays on and spindle motor runs continuously.
Common Fault:
UC6 74LS04 (7713) LOGIC
Also check: UA1, UB4, UC2, UC4, UC7, UD3, and UD5.
When drive powered up, red LED stays on and spindle motor runs continuously.
Common Fault:
UC7 74LS00 LOGIC
Also check: UA1, UB4, UC2, UC4, UC6, UD3, and UD5.
When drive powered up, spindle motor runs continuously. Red LED may stay on, or flash three times and go out.
Common Fault:
UC8 74LS42 LOGIC
When powered up, spindle motor runs momentarily, but red LED doesn't come on. When LOAD attempted, screen indicates "SEARCHING FOR..." but red LED does not light and spindle runs continuously. Partial failure: no read, stepper doesn't move or just buzzes or chatters.
Common Fault:
UD1 7406 (M53206P) LOGIC
When drive is powered up or reset from computer, red LED comes on and goes out, but spindle motor does not turn. When LOAD is attempted, stepper moves slightly, spindle doesn't turn, and error message on screen is "FILE NOT FOUND" with flashing red LED. One failure causes motor to run continuously but drive works normally. This IC can cause good reads but corrupted formats.
Common Fault:
UD2 7407 or 7417 (M53207P or M53217P) LOGIC (R/W CONTROL BUFFER)
When drive powered up, red LED stays on and spindle motor runs continuously.
Common Fault:
UD3 74LS86 LOGIC
Also check; UA1, UB4, UC2, UC4, UC6, UC7, and UD5.
Drive powers up and resets normally, but when LOAD is attempted, screen indicates "SEARCHING FOR ..." red LED does not light and spindle runs continuously.
Common Fault:
UD4 74LS123 LOGIC (MMV) no sub with earlier board 9602 IC!
Also Check: UE6.
When drive powered up, red LED stays on and spindle motor runs continuously.
Common Fault:
UD5 74LS197 (74177) LOGIC (TIMER)
Also Check: UA1, UB4, UC2, UC4, UC6, UC7, and UD3.
Drive powers up and resets normally. Spindle motor runs, stepper moves slightly, but "FILE NOT FOUND" error, and red LED flashes.
Common Fault:
UE4 LM311 COMPARITOR (READ)
Also Check: UF3 and UF4.
Drive powers up and resets normally, but when LOAD is attempted, screen indicates "SEARCHING FOR ..." red LED does not light and spindle runs continuously.
Common Fault:
UE6 74LS193 (BINARY COUNTER)
Also check: UD4.
Drive powers up and resets normally. Spindle motor runs, stepper moves slightly, but "FILE NOT FOUND" error and red LED flashes.
Common Fault:
UF3 NE592N (LM592) READ PREAMP
Also check: UF4 and UE4.
Drive powers up and resets normally. Spindle motor runs, stepper moves slightly, but "FILE NOT FOUND" error and red LED flashes.
Common Fault:
UF4 NE592N (LM592) READ AMPLIFIER
Also Check: UF3 and UE4.
When powered up, green power LED comes on and red LED comes on and goes out normally, but motors do not run (or move slowly). Drive access will produce a flashing red activity LED and error messages "file not found" or "drive not ready" on the error channel.
Common Fault:
VR1 UA7812KC (LM340KC-12) +12 VOLT REGULATOR
Note: A shorted Tantalum capacitor C15 can drop the +12V line!
Green (power) LED dim, flickers, or does not come on at all. Drive appears dead, but spindle motor runs continuously.
Common Fault:
VR2 UA7805KC (LM340KC-5.0) +5 VOLT REGULATOR
Drive appears dead, but spindle motor runs continuously with both green and red LEDs dim or dark. May be intermittent and fail after warmup. This part normally runs hot.
Common Fault:
CR1 - 2 AMP 200V BRIDGE RECTIFIER (FOR +5V)
Drive appears to power up normally, but motors do not run. Should get hot only if drive is accessed (motors running) continuously.
Common Fault:
CR3 - 2 AMP 200V BRIDGE RECTIFIER (FOR +12V)
-- Ray Carlsen --
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