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 Post subject: Re: Ten-Tec 1254 general purpose comm rcvr 100khz-30 mhz
PostPosted: Nov Mon 06, 2017 12:30 am 
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Joined: May Sun 28, 2017 9:08 pm
Posts: 202
Location: Whiteville, TN
Surface mount is a very tantalyzing solution. PCB traces would have to be cut in any case just to get any cap in there. SMD caps would be really elegant. Removing the green mask without removing the copper must be a real process!

Googled several Murata data and application sheets and most all have words that say these filters do not pass dc.

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 Post subject: Re: Ten-Tec 1254 general purpose comm rcvr 100khz-30 mhz
PostPosted: Nov Mon 06, 2017 2:10 am 
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Joined: Nov Wed 17, 2010 11:14 pm
Posts: 68
Hi Karl. Yes, that is true, they do not pass DC. However, no mention that DC cannot be applied. In any case, if the filter is destroyed by application of DC due to metal migration or another issue, it is wise to add the block and there is no ill affect.

The solder mask is usually not difficult to remove. Really depends on the quality of the mask. Some masks are incredibly tough and resilient. Pick an area on the card and try. Pick a safe zone and see how tough the mask is to scratch away. I use again the Xacto blade. As you scratch the green surface away the bare copper will show through.

If you feel uncomfortable with that approach, see if there are a set of nodes that you can bridge between with a leaded cap... after you cut away the required traces to the filter input and output. Small 0.1 uF or 0.01 uF leaded caps are readily available. If you need a few, let me know.


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 Post subject: Re: Ten-Tec 1254 general purpose comm rcvr 100khz-30 mhz
PostPosted: Nov Mon 06, 2017 2:51 am 
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Joined: Nov Wed 17, 2010 11:14 pm
Posts: 68
Karl,

I just took a look at the solder side of the 1254. There is a huge space--- area--- between the CF input and output points. Just cut the in and out traces at any convenient place and you can insert a set of leaded parts in line with those cut traces.

Alan


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 Post subject: Re: Ten-Tec 1254 general purpose comm rcvr 100khz-30 mhz
PostPosted: Nov Wed 08, 2017 12:15 am 
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Joined: May Sun 28, 2017 9:08 pm
Posts: 202
Location: Whiteville, TN
Filched two .1 pf caps from a junk CRT monitor board and mounted on solder side of radio. Had to use a Dremel on the trace. That stuff was THICK! Worked like a champ! Had a huge setback when I finished the thing. Was deaf as a post! I musta made the same mistakes as Pete!

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 Post subject: Re: Ten-Tec 1254 general purpose comm rcvr 100khz-30 mhz
PostPosted: Nov Thu 09, 2017 3:48 pm 
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Joined: May Sun 28, 2017 9:08 pm
Posts: 202
Location: Whiteville, TN
Next is to re-cap a Heathkit SG-8 signal generator and see where and why this thing is deaf.

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 Post subject: Re: Ten-Tec 1254 general purpose comm rcvr 100khz-30 mhz
PostPosted: Dec Wed 06, 2017 3:58 am 
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Joined: May Sun 28, 2017 9:08 pm
Posts: 202
Location: Whiteville, TN
Update: Rechecked EVERY construction step to verify each component is correct and in the correct position and oriented, ah, correctly! Found Q5 in BACKWARDS! Now all I have to do is get it off the board. I have a really good solder sucker with the iron and sucker in one tool. Open for suggestions since this three legged thing is really in there!

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 Post subject: Re: Ten-Tec 1254 general purpose comm rcvr 100khz-30 mhz
PostPosted: Dec Wed 06, 2017 5:19 pm 
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Joined: Nov Wed 17, 2010 11:14 pm
Posts: 68
If you have a pair of hemostats, clip them onto the HEAD of the device. Then with the 1254 exposing the solder side apply solder to all the leads. POOL the solder a bit and then apply heat to the POOLED area, the hemostats will provide enough weight that the part will just fall out. If need be gentle rock on the hemostats will assist in removal. Alan


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 Post subject: Re: Ten-Tec 1254 general purpose comm rcvr 100khz-30 mhz
PostPosted: Dec Wed 06, 2017 8:23 pm 
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Joined: May Sun 28, 2017 9:08 pm
Posts: 202
Location: Whiteville, TN
Avictor, you get the "genius" award for today! Dint have hemostats but did have very small wire. Looped two passes twixt the legs of the TO-92 case, pooled like you said, heated the pool and pulled. Came right out! Very hard to MAKE a solder bridge when you WANT TO! By the way, I tested the J310 with the DMM and it tested good. Will update later.

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