[time-nuts] SRS PRS10 repair

Brian M brayniac at gmail.com
Tue Aug 25 13:35:22 EDT 2015

The earlier suggestion of a missing inverter seems to be the right thing to
chase this evening. I was able to add an inverter and decode the first few
characters on a scope. I get the expected DC1-CR-P-R-S sequence.

Thanks for the input on this. I'll reply back after I've had more time to
hack at this.

- Brian

On Tuesday, August 25, 2015, Brian Inglis <Brian.Inglis at systematicsw.ab.ca>

> Hi,
> You have too many 1s in your startup string compared to the expected
> "PRS_10\r".
> If the MCU clock is not 10Mhz then the integrated UART rates will be off,
> which should produce framing errors, but do UARTs still detect and systems
> report these nowadays, or just pass along garbled data?
> Otherwise, garbled data is most often a result of inadequate pin contact,
> if the connectors are not seated properly, or the pins or sockets are loose
> in their shells.
> Age and rough treatment can have that effect.
> "Internal hardware jumpers allow these pins to be configured as analog
> outputs
> to monitor the lamp intensity and varactor voltage for complete
> compatibility
> with the FRS."
> Have you checked the jumpers in the manual Configuration Notes:
> "Pin 4: TXD/PHOTO The default configuration uses this pin as an output for
> RS-232 data.
> Many system parameters (including the lamp intensity) may be monitored via
> the RS-232
> interface. The function of this pin may be changed to an analog monitor
> for the lamp
> intensity by removing one resistor (R347) and installing a 10 kΩ resistor
> for another (R348)
> on the microcontroller PCB."
> On 2015-08-24 22:40, Brian M wrote:
>> I tried through the weekend, double and triple checking wiring and setup.
>> I've tried the following methods of getting serial comms working:
>> PRS10 -> Arduino Uno (with processor bypassed) -> USB Host
>> PRS10 -> Level Shifter -> BBB UART
>> PRS10 -> MAX232 -> USB Serial adapter
>> Shortly after power is applied to the PRS10, I do get a string of
>> characters. Believe it should be the model information. Instead I get:
>> wy+VPgy
>> I guess the good news is that this output appears consistent with each
>> power cycle of the device. And I'm getting the same results through all
>> the
>> hookup methods I've tried.
>> My minicom settings are for software flow control at 9600 8N1 - from what
>> the manual states, this should be the right settings. I've tried screen as
>> well - and get the same text. I went crazy trying several other rates and
>> setting combinations. No luck.
>> Maybe I've missed something obvious.
>> I agree that getting comms going to the MCU are going to be an important
>> step. How do people address this type of problem? Scope the serial and try
>> to decode by hand? The 10Mhz to the MCU looks OK on a scope. Are there
>> further steps people try after that? If nothing else I think there's some
>> interesting stuff to learn here. I also wouldn't mind tearing out the
>> electronics, determining if the lamp is good, and attempt to build from
>> there. I don't know the datecode for the unit, the PCB is marked with a
>> datecode suggesting 2003? I don't have the full case. I'm trying to assess
>> what are reasonable next steps. How do I determine if the MCU is healthy?
>> If the MCU is fried, how do I determine if I just need to squeeze a new
>> MCU
>> board in there?
>> Thanks! I appreciate the input so far!
>> - Brian
>> PS - after looking again at the signal on the scope, it does seem like it
>> is 9600 baud. ~100µS per bit. The data out on the MCU itself looks like
>> what I saw on the main connector.
>> On Sat, Aug 22, 2015 at 2:04 PM Mike Cook <michael.cook at sfr.fr> wrote:
>>> Le 22 août 2015 à 03:40, Bob Camp <kb8tq at n1k.org> a écrit :
>>>> Hi
>>>> On any microprocessor based gizmo, getting the micro running (again) is
>>>> generally priority number one. It sets everything up and gives you the
>>> diagnostic
>>>> info you need to go further. Garbled serial is better than none at all.
>>> It suggests
>>>> something short of a total MCU death spiral …
>>>> Bob
>>>> On Aug 21, 2015, at 7:26 PM, Brian M <brayniac at gmail.com> wrote:
>>>>> Dear list -
>>>>> I have come into possession of a for parts prs 10. I'd like to try to
>>>>> repair this device. What I've noticed so far. Serial is garbled. (Even
>>>> at
>>>> varying baud rates).
>>>   You don’t say how you are connecting to the Rb. The manual states:
>>> "RS-232 data is sent to the host on pin 4, received from the host on pin
>>> 7. The baud rate is
>>> fixed at 9600 baud, 8 bits, no parity, with 1 start and 1 stop bit. No
>>> DTR
>>> or CTS controls are
>>> used; rather, the XON/XOFF protocol has been implemented. The transmit
>>> drive level is 0
>>> and 5 V, not the +/-12 V normally associated with RS-232. These levels
>>> are
>>> compatible with
>>> most RS-232 line receivers, but does not require their use (a TTL
>>> inverter
>>> may be used
>>> instead), hence simplifies the interface when used inside an instrument
>>> at
>>> the sacrifice of
>>> degraded noise immunity over long lines."
>>> So make sure that you adhere to that.
>>> Lamp isn't lit.
>>> What’s the date code. Early versions may be reaching EOL, though 20yrs id
>>> quoted.
>>> Doesn't look great. I'd like to know
>>>>> if anybody else has wandered down this path. What are common failure
>>>> modes?
>>>> Anything match up with what I describe? Voltages to check would be
>>>> helpful.
>>>> The 10MHz out looked okay on a scope. Haven't gone further yet. I
>>>> suspect
>>>> the crystal is fine.
>>>>> Thanks in advance. Happy hacking!
>>>>> - Brian
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