Manufacturer:Ann Arbor Terminals Inc.
Model:Ambassador, 5514 2459
Serial Number:52743-1-1
Year of Manufacture:1984 (IC date codes, e.g. 8408)
Date of Receipt:2024
Source:UVic Lib (for refurbishment)
State upon Receipt: Good physical condition but not functional (no activity at power-up).

Date:2024
Symptoms: No activity at power-up.
Analysis: No output from power supply. Power supply schematic traced. NE5561 oscillator is active, but no switching at output even though input conditions should enable switching.

Date:2025 Aug
Analysis: Power supply cont'd. NE5561 removed, checked in test circuit, still no switching at output.
Solution: NE5561 is obsolete.
Circuit redesigned to use UC1845 - see new schematic.
  • Voltage sense divider adjusted: 1845 ref is 2.5V while 5561 is 3.75V.
  • Current sense R altered: 1845 shutdown is 1V while 5561 is 0.5V.
  • Oscillator set to 2 times target switching frequency due to 1845 internally halving the frequency for 50% max duty cycle. 5561 circuit was designed for 50% max by voltage divider bias on Q104.B. In theory this is at odds with the sync to line-scan, but just means the sync is on every 2nd cycle.
  • R110 removed to keep Q104 from limiting operation after power-up.
  • Output circuit altered as output assert state differs.
Unit functional, voltages good, but V-5 is -6.1V.

Date:2025 Aug
Procedure: Diodes D105 & D106 appear to have been type-swapped during manufacture (presumed error), as the GI850 type (installed for V+12) has higher current rating than the RGP20 type (installed for V+5). Diodes swapped to correct. Also affirmed by MR850 type listed for V+5 in manufacturer schematic for the power supply early version.

Date:2025 Sep
Procedure: Monitor adjustments tweaked for some improvement. Brightness adjusted up significantly from prior setting.

Date:2025 Sep
Procedure: Configuration-RAM battery voltage is 3.26V.

Date:2025 Sep
Procedure: Two rear feet on keyboard decayed, replaced.


  Unit Log
Ann Arbor Ambassador Terminal 		bhilpert
2025 Aug