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

Reply to
Gord S
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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

-- dave06a@ Low-cost firmware development tools:

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Reply to
Dave Dunfield

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

Dave Dunfield wrote:

Reply to
Gord S

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

Clif Holland wrote:

Reply to
Gord S

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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
Reply to
Gord S

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