[DSP-10] Continuing troubleshooting

[Scott]

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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