[DSP-10] Continuing troubleshooting

[Scott]

Hey!  I found I have the original article PDF files on my PC!  :)

I would check these points:

D1, Pin A2 for 0.7VDC in TX
U4 Pin 3 for about 3.5VDC in TX
U4 Pin 1 for maybe 1.5VDC in TX.  Not too important as long as it's not 
0VDC or higher than Pin 3.
U5 Pin 3 for about 5.25VDC in TX.
U5 Pin 1 for maybe 2.5VDC in TX.  Again, OK as long as it isn't 0VDC or 
5VDC in TX.
Q2...Measure at emitter (in TX)...guessing 0.5 to 1.5VDC.  Measure Base 
in TX.  Should be about 0.6VDC greater than the emitter voltage.  
Collector should be +10V in TX.

If all those are good, check solder joints at C41, C43, C45, C51, C52 
and C53.

That's about it.  That covers the entire section that is for the 
transmitter only.  The other circuitry is shared with RX, so if it is 
indeed working OK in RX, all those sections should be good.

Scott
N0EDV


On 4-12-2013 23:21, Scott wrote:
> Yeah, been keeping a low profile here...all those black helicopters 
> overhead!  HI HI  ;)
>
> I'll see if I can get access to the schematics and give you some 
> ideas.  I'm betting you have a fairly simple problem since you seem to 
> be getting some SSB power out.  What is the unit supposed to put out?  
> I think you mentioned a 2N5109 as the PA?  If so, I'll guess maybe 1W 
> output or so is expected?
>
> I'd check for DC voltage on the collector of the PA transistor.  It 
> may be applied both in TX and RX or maybe just TX.  Whichever it is, 
> check to be sure it's there at least during TX.  That is a trick I use 
> on my old Icom 251A 2M radio I use as an IF for my microwave 
> transverters.  I basically remove the DC supply wire to my PA 
> transistor and the "leakage" coming through the now dead stage is 
> about -8 dBm at the antenna connector, so it would be believeable to 
> me that you could get your 2-3 mW of "leakage" through a dead PA 
> stage...of course, any driver stage could have the same issue.  Does 
> it use MMICs anywhere in the transmit path (such as MAR-4, ERA-1, 
> etc.)?  If so, check for voltage on the input and output sides of 
> them.  The output side is usually something between say 3.5-5V and the 
> input side is less, something like 1.5-2.5V.
>
> Scott
> N0EDV
>
>
> On 4-12-2013 21:18, Don AE5K wrote:
>> On 04/12/2013 04:09 PM, Scott wrote:
>>> Not familiar with the schematics, but I would say the +10T would go 
>>> to +10V when switched to TX mode.  If you have 0V, is there a 10V 
>>> regulator (perhaps 7810?) that could be bad.  If so, is there 
>>> voltage at the input to the regulator?  If there is and no output, 
>>> it could be a bad regulator IC or the +10T line shorted to ground.  
>>> If you have a link to the schematic, send it to me and I'll take a 
>>> look.
>>>
>>> N0EDV
>>> Scott
>>>
>>>
>>> On 4-12-2013 21:02, Perry Ogletree wrote:
>>>> ??????????????????????????????????????????
>>>> -----Original Message-----
>>>> In tx mode, the +10T line is zero.
>>>> ??????????????????????????????????????????
>>>>
>>>> Isn't the +10T line supposed to be +10 volts IN transmit, not 0 
>>>> volts.  As I
>>>> recall, that line was the power for the PA chain. That would 
>>>> explain your
>>>> low power readings!
>>>>
>>>> Perry - K4PWO
>>>>
>>
>> Gee, another eagle eye.  Thanks Scott.  Haven't heard from you in a 
>> while.
>>
>> The original schematic(s) appeared in the 3 part article on the 
>> DSP-10 in September, October, and November 1999 QST by Bob W7PUA. If 
>> you are ARRL member, you can see them in their archives.  I think 
>> they are also available on Bob's DSP-10 page too.
>>
>> I know I have awaken this reflector -- probably the most traffic in 
>> years on it!  I can use eyes looking at my problems and proposing 
>> tests or "just tell me what's wrong" hi.
>>
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>

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