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

"Bitrex = ****wit "


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.

** FFS - try attaching an antenna - ****WIT !

In my area with most receivers I get plenty of strong
stations with no external FM antenna.

** Blatant LIE.

FM receivers normally give no output with no antenna.

Portables and clock radios have ANTENNAS !!!




.... Phil

On 12/1/2011 1:37 AM, Phil Allison wrote:
"Bitrex = ****wit "


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.

** FFS - try attaching an antenna - ****WIT !


I don't own a proper a FM antenna. I almost never use a receiver to
listen to the radio. When I do I get plenty of strong stations with no
external antenna, as I mentioned.

In my area with most receivers I get plenty of strong
stations with no external FM antenna.

** Blatant LIE.

FM receivers normally give no output with no antenna.

Portables and clock radios have ANTENNAS !!!


I live about eight miles from several 40,000-50,000 watt ERP FM stations
- the other receiver I have here picks them up just fine with great
sounding audio without an external antenna. It's magic!



... Phil

"Bitrex = ****ing ****wit "


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.

** FFS - try attaching an antenna - ****WIT !


I don't own a proper a FM antenna.


** Use a length of WIRE - ****HEAD !!!


I almost never use a receiver to listen to the radio.


** ROTFLMAO

What does this cretin use then - ESP ??


When I do I get plenty of strong stations with no
external antenna,

** FFS - go **** yourself.

WOT A MORON !!!



..... Phil

"Phil Allison" wrote in message
...

"Bitrex = ****wit "

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.
** FFS - try attaching an antenna - ****WIT !

In my area with most receivers I get plenty of strong
stations with no external FM antenna.
** Blatant LIE.
FM receivers normally give no output with no antenna.
Portables and clock radios have ANTENNAS !!!

Sorry, Phil... Tuners and receivers often have an output without an antenna
attached. This is due to poor shielding of the front end.

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

On 12/1/2011 8:56 AM, Tim Schwartz wrote:
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

Thanks for your reply. I did a bit more work on the unit today, using a
random wire antenna and checking out the waveforms going into and out of
the FM IF IC. The audio output from the IC is weak, noisy, and appears
to be half-wave rectified. I can't see any signal at all going into the
demodulator IC, down to the limit of my scope (5 mV/div with 1x probes.)
Obviously there must be some signal there to produce any output at all,
but I would think that with 2 stages of RF and IF amplification before
the demodulator IC there should be some signal visible there at the IF
frequency. This makes me think that the problem is in the FM front end
somewhere.

As for AM, I think I may just get an "aftermarket" loopstick antenna and
mount it to the receiver somehow.

In article ,
Bitrex wrote:

Thanks for your reply. I did a bit more work on the unit today, using a
random wire antenna and checking out the waveforms going into and out of
the FM IF IC. The audio output from the IC is weak, noisy, and appears
to be half-wave rectified. I can't see any signal at all going into the
demodulator IC, down to the limit of my scope (5 mV/div with 1x probes.)
Obviously there must be some signal there to produce any output at all,
but I would think that with 2 stages of RF and IF amplification before
the demodulator IC there should be some signal visible there at the IF
frequency. This makes me think that the problem is in the FM front end
somewhere.

Could be... possibly a fried first-stage RF amplifier? Depending on
the design, these may be vulnerable to damage due to induced voltage
from (e.g.) a nearby lightning strike, or even just bad static
electricity on the feedline.

Or it could be in the detector / demodulator. The FM detector usually
contains multiple gain stages within itself, with the "limiter"
cranking up the gain until the signal is clipping fairly cleanly. A
feedback loop (the AGC) controls the amount of added gain in the
detector, and the AGC voltage is often used to drive a signal-strength
indicator.

So, you could have weak (or no) signal coming into the detector, or
you could have a detector whose gain stages or AGC loop are frotzed.

Next step is probably to kluge together some sort of FM signal source
which you can use to inject a few millivolts (or microvolts) of RF
into the circuit via a probe, work backwards, and find out how far
back towards the front end (and how little RF you can inject) to get
it working.

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

"Tim Schwartz" wrote in message
...
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



Personally, its a very nice receiver when working properly.

Yeah, but it may indeed require alignment after all these years. Onkyo's
seem to drift in their adjustments as they age.

Mark Z.