CurtPalme.com Home Theater Forum

[Curt Palme]

So I have this 25 year old Akai GX 635 deck here for service, two of them actually. ONe deck had no play or record, the other had no record.

Turns out the input preamplifier transistors, typical 2SC 458 little TO92 packages are either changing gain, or are intermittent. Supply voltage is 12 volts, they are driving very low levels of signal and current, yet they are intermittent and change gain.

I pulled a couple out of circuit on the dead channel, the voltage specs are all over the map before I pulled them out, they tested OK, so I put them back in circuit, and then I had the channel working. Thinking it was a bad solder joint, I left the deck alone but running on the bench. I watched as the gain dropped, then rose again. WTF?

I changed the transistors and the deck is now solid. In everything I've worked on before, I've never seen this. I wonder if the original transistors had a bad production run, similar to the G90 chip?

[Curt Palme]

So I have this 25 year old Akai GX 635 deck here for service, two of them actually. ONe deck had no play or record, the other had no record.

Turns out the input preamplifier transistors, typical 2SC 458 little TO92 packages are either changing gain, or are intermittent. Supply voltage is 12 volts, they are driving very low levels of signal and current, yet they are intermittent and change gain.

I pulled a couple out of circuit on the dead channel, the voltage specs are all over the map before I pulled them out, they tested OK, so I put them back in circuit, and then I had the channel working. Thinking it was a bad solder joint, I left the deck alone but running on the bench. I watched as the gain dropped, then rose again. WTF?

I changed the transistors and the deck is now solid. In everything I've worked on before, I've never seen this. I wonder if the original transistors had a bad production run, similar to the G90 chip?

[Sparky015]

If they were pressed to far down on the board, it's possible one of the legs broke inside the transistor body and was intermittent. We have similar failures like that at my work.

Paul