Unit 2613

Serial Number:2613
Year of Manufacture:1982 (77xx to 82xx date codes)
Date of Receipt:2019 Aug
State upon Receipt: Functional but whistles come and go, varying in both frequency and level. Frequency setting seems off by -10 KHz and excessively wide, e.g. station at 1070 is clearer with switches set at 1060.

Date:2019 Aug
Symptoms: Whistling observed to disappear with a finger in proximity to the xtal on the 2nd LO board. This suggests the 2nd LO PLL is failing to correct the 2nd LO. Whistle/tuning problem goes away when 2nd LO board from other unit is swapped in.
Procedure: Extender card constructed.
Varactor voltage is ~7500Hz oscillation. F of VXCO is 19.52600 rather than 19.5625. Trimmers marked with white piant dots to mark original position. L1 turned a few degrees CCW to bring to correct F. PLL now locks in and maintains F. Whistling gone and tuning now correct.

Date:2019 Aug
Symptoms: VFO mode does not work. Belt drive between knob shaft and pot is stripped due to deteriorating plastic links.
Procedure: Belt replaced with a 1/8" * 1.5"ID neoprene O-ring. Less than ideal but works for light use. Pot positioned to center with limits pin at center. Also, 4 spacers separating clutch sections trimmed down to 1-3/16" (removed <1/16") for better engagement of clutch.

Trimmers adjusted for VFO range. Monitor VFO board A4.6 with frequency counter. Adjust for 13,910.0 KHz @ 0 (trimmer nearer front), 13,901.0 @ 9 (trimmer nearer interior). Resultant knob travel limits are ~ 0.400 KHz below 0, ~ 1.4KHz above 9.

Date:2019 Aug
Procedure: One short aluminum spacer on front end board had been broken, replaced with steel DB-25 spacer.

Date:2019 Aug
Procedure: One aluminum spacer for filters module mount has broken male thread section. Both Al spacers replaced with stainless.

Unit 2621

Serial Number:2621
Year of Manufacture:1982 (78xx to 82xx IC date codes)
Date of Receipt:2019 Aug
State upon Receipt: Optional noise blanker board not present. Missing module covers for synthesizer, receiver & power supply. Had been worked on earlier in 2016, label from then says ref osc bad. Osc oven seal is unsoldered, can cover can be removed.

Not functional. Audio comes and goes with slight touches of noise blanker knob. Won't tune, KHz knobs ineffective, MHz knobs may bring up a scanning effect that may or may not settle on some station.

Date:2019 Aug
Procedure: Noise blanker control pot loose, tightened. Unit now tunes and audio cut-out gone. Probably due to intermittent contact of GND lug on pot throat.

Date:2019 Aug
Procedure: Slip pins installed on power wires for xtal reference module, so it can be installed removed without soldering.

Date:2019 Aug
Procedure: Preselector removed to see if gain control could be made smoother. No, 3-gang pot. Unit reverse-engineered as it differs from schematic in 83 manual.

Date:2019 Aug
Procedure: Modules removed and cleaned. Aluminum carved out from front-right corner of synthesizer module to allow screw to seat without binding (previously chewing off Al with each turn).

Date:2019 Aug
Procedure: After reassembly, tuning fault has returned. Traced to bad contact on coax connector at 5MHz input to synthesizer. Female center contact on plug appears to be widened, so not gripping socket pin properly. Simply rotated to active position (not a comprehensive solution). Functional again.

Date:2019 Aug
Procedure: 2 keys in edge connector for translator board had been mashed, replaced.

Date:2019 Aug
Symptoms: VFO belt stripping.
Procedure: Belt replaced with a #127 (3/32" * 1&5/8"OD) neoprene O-ring. Pot positioned to center with limit pin at center. Also, 4 spacers separating clutch sections trimmed down to 1-3/16" (removed <1/16") for better engagement of clutch.

Trimmers adjusted for VFO range.

Date:2019 Sep
Symptoms: In VFO mode, reception cuts out when VFO is turned below 0 (CCW).
Procedure: Appears VFO is cutting out with too much bias on varactor.
VFO board L9 turned ~ 1/2 turn CCW (raising F of VFO), so bias on the varactor can be reduced via trimmers. Trimmers readjusted for VFO range.