On 11/30/2011 7:04 PM, Bitrex wrote:
I have an Onkyo TX2500 mk II receiver that I'm hoping to fix up for a
friend, which is not working properly on AM or FM. Tuning to AM gives
low frequency oscillation, and a cursory inspection shows that for some
reason someone has physically snipped off and removed the external AM
loopstick antenna. Since the loopstick coil appears to be integral to
the AM tuner, this was a pretty dumb thing to do and I'll have to find
some kind of replacement to get AM working again.

Tuning to FM with the muting on gives no output; disengaging the muting
circuit, with no external antenna, I get static and a few very faint
stations. In my area with most receivers I get plenty of strong
stations with no external FM antenna.

If I put my finger across the FM terminals as a makeshift antenna I get
better reception and some strong stations, but even when they're tuned
in strongest they're noisy and badly distorted, and the voltage on the
transistor collector controlling the "LOCKED" lamp never falls to engage
the lamp (the lamp itself is burnt out.) Stereo decoding never engages
either.

On FM the "SIGNAL" meter is completely dead, even when a (distorted)
signal is booming in. The "CENTER" meter does deflect in response to
signals, but it only seems to deflect in one direction.

All power supply rails test close to the indicated values on the schematic.

I haven't done much work on these old receivers, so before I pull out
the scope and multimeter can anyone give me any pointers on what area to
suspect? The way the meters are misbehaving leads me to suspect that
the FM IF/demodulator IC HA1137 or associated circuitry is faulty.
Thanks for any advice.

Here's a schematic of the FM tuner section:

http://i227.photobucket.com/albums/d.../Onkyo2500.jpg

Good morning,

The missing AM antenna will be a show stopper for the AM.
Unfortunately is is not uncommon to see these ripped off the receiver.
People seem to think they make a great handle. Finding a junk unit with
a good antenna might be your only bet.

As to the FM, these do require an external antenna. An inexpensive
Dipole will likely do if you are in a good reception area. SOME
receivers will not do proper MPX if the MPX light is burned out. I
don't remember if the TX2500-II is one of those or not.

Personally, its a very nice receiver when working properly.

Regards,
Tim Schwartz
Bristol Electronics