Projector Bench

A Failed Speaker on the EIKI NT

The EIKI NT which I had purchased on eBay had ceased to play any sound through the forward-pointing speaker that’s mounted in the rear cover. For quick previews of sound films, this internal speaker usually suffices.

photo of internal speaker in rear cover
The rear cover of the EIKI NT showing the front-facing internal speaker.

Some detective work was required to track down why this speaker was not working.

I noted that the exciter lamp was still glowing, so I connected the two external speakers in the removable front cover to the speaker output socket on the front of the projector. Flicking a piece of paper past the sound drum produced thumping in these external speakers. Hence the photocell and the amplifier were working. It had to be a problem with the internal speaker.

I removed the rear cover and unplugged the internal speaker cable, which is connected via a 3.5mm tip and sleeve plug and socket on the amplifier chassis. Rigging up some plugs, sockets, patch cables and alligator clips, I was able to connect the external speakers into this internal speaker output socket. These produced sound loud and clear. Hence signal was being fed to the internal speaker.

By this stage it was looking like the internal speaker itself was the culprit. Finally I took the obvious step of measuring the speaker resistance and it was open circuit. There was nothing for it but to remove the internal speaker, inspect it more closely and probably seek a replacement.

I removed the four bolts securing the internal speaker and un-soldered the two connecting wires. I then re-fitted the bolts, spacers and washers to the plastic case so they wouldn’t go missing.

I then capped off the 3.5mm cord plug on the internal speaker cable with a matching cord socket to prevent it touching anything inside the projector — the internal speaker socket on the amplifier chassis is rather close to the 240v wiring and main power switch!

A 125mm 8 ohm replacement speaker driver was needed. Not an easy thing to come by — readily available ones from the usual suppliers were 4 ohms. In the end I contacted Frank Arnstein at projectorheaven.com.au. Fortunately Frank had a second hand EIKI NT speaker available, which was duly ordered and arrived in a few days.

The replacement driver was not in quite the same near-pristine condition as the faulty one. It needed a clean up to remove dust and light rust. Most noticeably the black grille cloth over the front of the unit was in poor condition.

I was able to remove the good grille cloth from the failed speaker and, with the help of a little “magic tape” to hold it in position, re-glue it to the front of the replacement unit, as shown in the accompanying photograph.

photos of speaker repair
The new speaker driver had badly weathered speaker cloth. I was able to remove the speaker cloth from the failed speaker and glue it onto the replacement unit. The sticky tape is holding it in position while the glue dries.

As a precaution, before fitting the new speaker into the projector I measured the DC voltage at the internal speaker output using a 3.5mm plug with flying leads and a digital multimeter to test if there was perhaps some DC leakage which had caused the previous speaker to go open circuit. Nothing showed up, so the failure remains a mystery.

I then re-soldered the replacement speaker onto the internal speaker cable and re-fitted the unit carefully into the rear cover, taking care to position the speaker terminals to the rear of the projector to keep them away from the AC wiring to the power transformer.

photo closeup of new speaker in position
The new speaker mounted into the rear cover and wires re-soldered. All working again!

Flicking paper across the sound drum produced a healthy thump. Things were working again.

In the next post, we will look at a broken belt on the same EIKI NT which arose shortly thereafter.