PCB marking H.E.C H13A V LT-1112 Sharp F6139
4 LEDs stopped working on one channel of the VU meter (right channel, bottom 4 green). The PCB markings only gave one hit to something similar https://www.eevblog.com/forum/repair/pioneer-cassette-player-wanted-vu-meter-pioneer-ct-s99rw-display/ The display bar graph is almost identical. This led me to Sanyo chip IR2E28. The only datasheet didnt have a compatible model, as mine goes from -20 to +9dB. Mine also just has the classic black blob protecting a printed on processor of some type. You can see the LEDs lighting through the single sided PCB, so they must be early SMD type printed onto the PCB. The white diffuser block is held in place by the usual hot stamp/leg melt meaning removing it will need another method the re-attach. Small screws or superglue. No space for hot glue.
The blob has 15 tracks to the LEDs. 14 leds and common anode to +V. I think it must be multiplexed to ensure a consistent brightness, but that would only need 9 tracks, or even 8 (4 leds + 4 commons). I started exploring simple comparitor circuits to just drive the bottom 4, so scraped a few tracks to ensure the existing LEDs are ok. I used a 10k to +V (13V, not a typo, taken from service manual) and discovered that the -20dB led had failed. In replacing this, the remaining 3 started working. I haven't stopped to reflect why this might be.
For me, the easiest method to replace the LED was to remove the corner and slide a new LED in. There is a bezel (~4mm) where the PCB fits into the front panel so any mod has to take account of it. The replacement LED was an old bar graph type from the 80s, so the colour and current draw was likely identical to the original. I did cut the top off the led, and sand off the larger white side and trim the sides. This lit the new 'top' face well enough. On reflection it would probably have been quicker to remove the diffuser and solder in a smaller rectangular one that fed up inside. Newer SMD LEDs take little current and are very bright, so I doubt it would have looked right.
You can't tell the difference once installed. Finger's crossed more LEDs don't unbond.
