[GreenKeys] Dovetron Repair

[John Spigel]

Hi guys, thanks for all the suggestions. I hadn't thought about actually 
using a polar relay on the +/-outputs to place in the loop. As of Sunday 
I have the afsk audio working after replacing a bad XR2206. It now has 
the audio and I am thinking about changing from the factory settings to 
the more useful 2125 with 170 and 850 shifts and the apply a +/- input 
to see if afsk actually is working. My unit has the four audio shift 
adjustment trimmers mounted on a tiny circuit board hanging on the front 
panel wide/narrow switch. Much does not follow the standard circuit 
diagram! I'm still trying to get all the LEDs working. I have no signal 
loss LED and the loop light flashes very dimly and not at the right 
threshold setting. Some discrete LEDs on the SSD don't light as well. 
Possible bad 741s somewhere. I have already replaced a couple.

I have a few polar relays to try. And yes, there are some pretty clever 
device testers out there. Some can even identify what you plug in! Just 
got to figure out which one I need!

73, John W1AN

On 13-Feb-24 03:33, B. Smith wrote:
> A handy device is an op amp tester.  The one pictured came as a kit. 
> It has a zero insertion force socket which is kind of neat.
> Note that some op amp brands out perform others and I think that is 
> mentioned in the Dovetron manual.
> See attached.
>
> Polar relays can be tested and adjusted.
> http://k4che.com/Polar%20Relay%20Test/Polar%20Relay%20Testing.htm
>
> K4CHE
>
> On 2/12/2024 8:25 PM, Tom Hunter wrote:
>> John Spigel,
>>
>> I have recently repaired two 1000Ts and am fighting with an MPC 1000. 
>> All Doverons are basically similiar.
>> The mark and Space tuning, the filters, etc are all the same.
>>
>> It helps to have a decent oscilloscope and a handful of 741 opamps 
>> for substitution.
>>
>> I believe you said you have a 1000T. If you want to key a loop with 
>> it you must use a polar relay (255A - tricky to adjust) or if you can 
>> find one, a 314A which needs no adjustment. I connect my relay to the 
>> +/- 12 volt output and use it  to key an external 60-mil loop. The 
>> 'scope will show you if you the polar outputs are working before you 
>> connect the relay.after that the relay chatter will prove they are 
>> working.
>>
>> My problem with my MPC 1000 is that the signal loss light flickers on 
>> space. When signal loss is activated it ties the unit up in mark 
>> hold. Mine works fine on the bench but acts up in the rack. I am 
>> stumped!
>>
>>
>> Tom   N3CRK
>>
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