24
edits
DC503/Repairs: Difference between revisions
Jump to navigation
Jump to search
attenuators, -22v rail
No edit summary |
(attenuators, -22v rail) |
||
| Line 1: | Line 1: | ||
==Repair Issues== | ==Repair Issues== | ||
* If no LED or display segment is lit after | * If no LED or display segment is lit after turn on, check for +15 V from U500 Voltage regulator IC type 723. | ||
* All ICs are placed in IC sockets. [[bad TI IC sockets|Contact problems can occur]]. Removing and inserting ICs may help temporarily. | * All ICs are placed in IC sockets. [[bad TI IC sockets|Contact problems can occur]]. Removing and inserting ICs may help temporarily. | ||
* Check board is mounted to frame with plastic washers in between near pcb conductor tracks, otherwise a short to GND can occur. | * Check board is mounted to frame with plastic washers in between near pcb conductor tracks, otherwise a short to GND can occur. | ||
* If the display responds properly to knob positions but not to input signals, check the signal coming out of the attenuators; on mine these switches seem to make poor contact. Also check the -22V rail. | |||
== Overheating / overvoltage == | |||
A bad TM504 PNP pass transistor damaged the -22V regulator circuit in my DC503, necessitating replacement of Q540, Q545, Q548, and R548. In spite of this exposing everything on the -22V rail to around -35V, it doesn't seem to have damaged anything outside the regulator. | |||
The only symptoms observed were R79 getting very hot and the unit not responding to input (though I _think_ the latter is due to an attenuator issue). | |||
[[Category:Instrument repair reports]] | [[Category:Instrument repair reports]] | ||