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imix500 6th August 2007 01:46 AM

Adcom GTP-450 Remote
Hey all, I recently aquired a GTP-450 preamp. The preamp works great but the remote (RC-45 II) is DOA. With a new set of batteries I get nothing out of it.

I've metered the IR LED and the two driver transistors and I don't see signal at the LED or either transistor base.

Apparently Adcom changed their remote codes very frequently, I can't seem to find a universal remote that can control the 450.

Is there any hope? Thanks!

anatech 6th August 2007 02:53 AM

Hi imix500,
Often the ceramic resonator leads break off. You can carve a bit into the housing and solder a new wire on. Clean the housing and PCB in that area and use RTV or something similar to glue the resonator down and resolder.

I use a 'scope across the IR diode to watch for activity. I even built an IR pulser and receiver with an LED and 'scope output for dealing with remotes and other optocoupler applications.

Good luck on your repair. Don't discount poor battery contacts and PCB connections.


imix500 6th August 2007 03:13 AM

Hey Chris, I assume that's what the two yellow components that look like MKP caps are.
Is there a way to test them with a psu, dmm and a scope?

Otherwise I'll try to dig into the housing a bit. They were among the leads I reworked.

I'll look at the diode on my scope.

I metered 2.9v at the lytic cap and at both driver transistors. I just found the data sheets for the two driver chips, so I'll meter power there.
There's also a good amount of rosin around the resonators, so I will try to clean them. Thanks!

anatech 6th August 2007 03:34 AM

Hi imix500,
Simply desolder them. A broken lead would be impossible to miss then. :D Take corrective action if you need to and bond the resonator to the PCB when done.


Is there a way to test them with a psu
See if they oscillate when you press a key on the remote. Use your scope and a X10 probe. 200 ~ 700 KHz is a normal frequency range for simple remotes. The frequency should be marked on the part.

A DVM would only be useful for raw supply. IF the filter cap is bad, you would see noise on the power supply lines. That could confuse the uP in the remote.

Good luck on it! I've repaired many different kinds of remotes.


Edit: Don't forget to clean the PCB contacts for the buttons and gently clean the carbon "buttons". Use alcohol and a "Q-Tip".

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