Ideas? Kenwood TM261A reset problem

I have the basic "instruction manual" and a schematic with RF
adjustments diagram......No service manual.

Problem - Unable to effect a reset of any kind. Radio "stuck" in
current configuration, and operational otherwise. Does not appear to be
in lock mode. Function button does not cause a change into function
mode (no menu's displayed etc).

Operationally - Radio works fine on previously programmed channels and
is stuck with the display in CHANNEL mode.
- Good tx output and waveform
- Good tx deviation
- Good receiver operation - DTMF operates
- Radio LCD display normal and shows channel change and s-meter bar
graph and whatever was programmed previously.
- Display does NOT show it's locked (no key symbol).

Observations - Front panel pushbuttons all cause a beep to be emitted
when pressed and a second beep to be emitted if held in for
approx 1.5 secs. Because the programmed channels work ok (DDS ok
assumed) and the push buttons all cause a beep to be emitted
(generated by the microprocessor IC201) , it would seem that that IC201
is functioning. The inability to reset or cause a change into
"Function" mode (both with a particular change of display) leads me to
wonder first how it won't reset. I see IC209 (PST9130NR) labelled RESET
and input to the processor as RESET but I don't see any control to this
other than basic ON/OFF power. IC209 appears on the schematic to be
basically a 3 terminal regulator with the output TP tagged at 4.7
vdc.......I measure 4.8 vdc (likely ok). Is this some sort of power up
buffer or delay?

Checking pins of IC201, with the radio operational, appears daunting due
to it's location underneath the hard wired LCD.

Has anyone had a similar troubleshooting experience with this radio OR
knowledge of how the RESET works OR what might be locking the
microprocessor IC201? Might the EEPROM IC210 (X25160S1-2.7) be locking
IC201 (thinking about why the processor won't reset here.......perhaps
the EEPROM is disabling the micropro somehow?).

At this point, short of finding a problem with the RESET circuit (once I
know how that works), it would appear that replacing the front panel
module would be the only recourse.

Any constructive suggestions welcomed.


Gord - VE1AJF

 

You have tried a full reset (MR + Power on) correct???

How about a little history on how it got this way, IE was modding the
radio????

 

I have the basic "instruction manual" and a schematic with RF

Thats an odd one... I can only offer a bit more information to help
diagnose this - sorry if you already know this, but from your post I'm
not sure so here goes...

Anything labled "RESET" on the schematic is likely related to the
physical reset need to start the microprocessor properly. The fact
that you have displays, beeps and some front panel activity tells
me that the microprocessor is running. Physical RESET normally
only happens at power on, and IC209 is likely just a reset pulse
conditioner (holds reset low for a period of time after power has
stabalized).

The microprocessor normally stores it's permanent operating
parameters in the EEPROM - when you press buttons to change
modes, set parameters etc. It write the updated settings to the
EEPROM and reads it when it needs to know those settings.

What is referred to as "resetting the radio" is normally some key
sequence at power-up which causes the microprocessor to read
a set of factory default parameters from it's internal ROM, and write
those parameters to the EEPROM - this effectively wipes out any
user programming, and should cause the radio to behave exactly
as it came from the factory.

When you say "unable to effect a reset", I assume you mean that
you have tried the appropriate keys at power-on, and the radio is
not returning to defaults.

Given that we know the processor is running, and that it can access
the EEPROM (previously programmed channels and modes are
evident and appear to be as programmed), then I can see only two
likely reasons:

1) Problem with key matrix such that the keys are not being interpreted
correctly. If this were happening you should be able to tell (some
keys would do the wrong function etc.)

2) For some reason the microprocessor is unable to write the the
EEPROM - could be that the eeprom has gone bad. Some devices
have a write protect line, which the radio may be controlling, and it
may be in the wrong state (bad drive etc.)

I would check the data sheets on the EEPROM, see if there is a write
protect line, and observe it's state during an attempt to reset the radio.
If you have a logic analyzer or storage scope, look at the control signals
to the eeprom and see if the microprocessor is attempting to write it
during a reset attempt. If you can see valid write attempts, and the device
not write protected, yet the radio remains as previously programmed, then
replacing the eeprom might be a good next move.

If the microprocessor does not attempt to write the the EEPROM during
a reset attempt, then the problem lies elsewhere - perhaps in the key
matrix which would prevent the processor from getting the command to
reset - normally the reset jey-sequence *always* works (Can't be
disabled).

Dave VE3DRD

 

Good ideas Dave. The more I've looked at this thing, the more I keep
looking at that EEPROM on the schematic but was getting foggy as to how
it reacted maybe during a reset. Your description of probable
operation of the "reset" IC209 is how I'd pictured that. Sure would be
nice if I could just GET AT that EEPROM better! Thanks much, again,
for tossing your thoughts back.

73 - Gord VE1AJF

 

Howdy Clif. Yes I've tried the key sequence as you mentioned to no
avail (may have mentioned it in an earlier post). The owner (a
competent operator) indicated that the radio turned on like this at some
point and hasn't changed. Inside the rig appears untouched and original
with no mods or signs of rework. Rest of what I know is, as mentioned
in a previous post. Thanks for taking the time to read.

Gord - VE1AJF

 

UPDATE to my previous post:

---------------------------------------------------------------------------


I've since figured out how to gain access to the processor and
surrounding area (bend the LCD away from it's plastic cradle and then
slide the cradle up the pins allowing the display to further uncover the
board). Pursuant to suggestions and comments from Dave Dunfield, there
is no scanned input key matrix on this radio....individual pushbutton
switches pulling their respective input pins on the micropro to ground
as required - these all work (although they don't seem to agree with the
schematic which shows a variation of the processor from the one in this
radio).....trying all combinations of switches + power on yielded no
reset. Scoping the EEPROM shows that it's being accessed normally and
that the -WP pin is always HI enabling whatever the processor wants (not
locked). At this point it seems that the problem is, that, I can't get
the microprocessor IC201 to either RESET or to recognize a FUNCTION
request. It's funny that it otherwise seems to work and control the
radio correctly.

Does anyone have the service manual who'd look up the theory and
sequence of reset for either of these areas? Also looking for a
schematic which shows the microprocessor M38267M8L110FP (may be a later
model TM261A) vs the one I have showing the M38267M8L104P.

Any comments or further suggestions welcomed. As aside, I've also tried
to source a replacement front panel PCB though various Kenwood sources
who've been unable to tell me if this subunit is even available.

73 - Gord VE1AJF

 

I sent a reply to a bad address, oh well....