Help Repairing Trio Ka-5700

[Mrrnoname]

Hi all,

I have a Trio Ka-5700 amp in super condition. It has worked flawlessly for years. Recently *sometimes* when you power the amp on the left channel is very quiet. It also shows virtually no power on that VU meter (right is fine) Giving the amp a gentle tap on the top case, or any sort of flex\bump brings the audio back to that channel and the amp is usually fine for the rest of the session.

I have triple checked all connections. Cleaned all terminals on the rear (both inside and outside), cleaned all switches and dials and replaced any leads just in case. The problem persists and I'm now convinced it's a dry joint or cap inside. Also tapping the phono lead going in to the back seems to bring the signal back, so I *think* it might be around the input area at the back.

It's somewhat hard to diagnose as it's only occasional and the more you use the amp the less it occurs. It seems to be mostly when it's been off for a few weeks.

Is there anyone near (ish) to Bristol who repairs vintage kit and could take a look for me? (Happy to pay to have it repaired) I am also happy to drive some distance to get it looked at. I absolutely love this amp, it's my daily driver.


Thanks,
Max.

[jmcilkley]

I have a similar problem on my Sony amp. The sound is sometimes not there on power on, sometimes on only 1 channel and sometimes both. Turning up the volume usually restores the sound and then it runs fine. So finding the source of the problem is tricky as once the sound comes on it continues just fine.
Is your problem on just one channel or both?

[Mrrnoname]

Originally Posted by jmcilkley

I have a similar problem on my Sony amp. The sound is sometimes not there on power on, sometimes on only 1 channel and sometimes both. Turning up the volume usually restores the sound and then it runs fine. So finding the source of the problem is tricky as once the sound comes on it continues just fine.
Is your problem on just one channel or both?

Always one channel and volume independent. Adjusting the volume doesn't help at all. I suspect it's a dry solder around the input jack's on the rear but need someone with skills to help 🙂

[Goldie99]

Sounds to me a lot like either dirty / aged protection relay contacts, or eventually dirty input selector contacts - getting better when you 'tap' the amp suggests more the former.

Alan

[ajgriff]

Oxidised protection relay contacts are very likely to be the cause especially with an amplifier of this vintage. Should be a relatively straightforward repair. The Kenwood/Trio service manual is available to download free from Hi-Fi Engine.

Alan

[Mrrnoname]

I've spent some more time looking at this and I'm now 100% certain it's a bad connection around the input jack on the rear. Giving the phono plug the smallest touch brings the audio back every time. I've fully cleaned both inside and outside of the jack and used different leads. The lead is making good connection to the amp. Maybe a dry or cracked connection to the board?

Anyone near Bristol who can look at this sort of thing?

[ajgriff]

It does sound like a problem with a poor joint or similar especially if other input sockets work ok. If you're not confident about using a soldering iron to melt a few joints why not place a request in the 'Repair and Restoration Services Wanted' section of the forum?

Alan