Unit received in fair condition, front looks good, no deep scratches or missing paint, rear and bottom has very slight corrosion.
Unit will not come out of standby mode, cut bottom chassis for service access, found no issues with main amp board.
Powering up microcontroller (front panel assembly, MCU is a M50941-597SP), was able to get some response from VFD with CD DIR depressed. Leaving it powered up for a couple minutes does eventually result in normal amplifier operation.
Took the chance to check output offset (negligible) and re-adjusted bias for 18mV per service manual.
Pulling power off and allowing amplifier to cool, will mean the next round of power up will take minutes for amplifier to come out of standby, verified clock to MCU is correct and started, Vcc and AVcc were correct and present, tried external 5V regulator, changing input filter caps, trying a quartz 4Mhz crystal instead of original resonator, to no avail, slipped DMM probe and shorted MCU pin from -35V (VP/VFD bias voltage) to adjacent input pin (38 shorted to 39 or 37). MCU now real and truly dead (heard a small pop and immediately shut off the amp by pulling power cord out).
Opps, killed this little sucker.
Was unable to located MCU (PN M50941-597SP or M50941-589SP) even through obsolete component brokers/traders. Decided to cannibalize from another unit (got off eBay USA).
Rear inputs slightly polished to assure good shield contact, input board was removed for visual inspection.
Re-soldered power input board where joints showed signs of crack formation, re-soldered main amp board as well.
Cracked and oxidised joints on main PCB.
Reworked these
More inadequate joints
Main PCB cleaned up after rework.
Signs of cracking on transformer ribbon
Joints reworked
Reworked one joint on transformer input.
Service access panel flipped and re-attached with M3 washers and screws.
Speaker A & B switches cleaned and lubricated.
Ebay amplifier arrived in broken condition (likely due shipment damage, tone control’s smashed, power button smashed, will not turn on), returned.
Seller agreeable to sell just the front panel PCB for parts, procured front panel PCB alone.
PCB arrived, wrapped in aluminum foil and plenty of bubble wrap for ESD and shock damage resistance, front power switch PCB area found cracked and power switch pushed in.
Crack stop drilled and PCB trace patched.
Epoxy patch on front of PCB.
ESR measured on all front panel PCB capacitors. Qty 4 were replaced as follows
| Designation | Original values | Installed values |
| C80 | 220uF 6.3V Low Profile | 220uF 10V bent over |
| C92 | 220uF 6.3V | 220uF 10V |
| C89 | 10uF 50V | 10uF 50V |
| C83 | 10uF 35V | 10uF 50V |
Power switch desoldered, new power switch soldered, cracked PCB trace patched over with enameled wire, crack stop-drilled with 1/16” drill bit. Solder side PCB lightly sanded and epoxy applied over cracks, top side sanded and a small patch applied with epoxy as well.
Power ribbon pads on front panel PCB slightly damaged during removal (qty 3), post soldering power ribbon connection, extra 3 enameled wires were used to jumper over to the ribbon connections and held down with Dow Corning 3145.
Jumper wires on front PCB
Unit tested and verified to power up instantly upon application of wall power.
