Old uniden Grant PC-196aa board

[Robalo]

I have an old Uniden president GRANT SSB radio with pc-196aa. I've replaced the D54 with a in4003. The radio powers on consistently well now. I still need to find the value of the d21 and d22 as they have been damaged, also clarifier has been modded. I'll on the search for the schematic or service manual, so If anyone happens to know where I can find or have them it would be appreciated. On the d54 i found a diode with the numbers 1R R170, I've never seen it before so if you have a clue as to about these parts please send them my way.

 

[Robalo]

President Grant

 

[tecnicoloco]

Check a Realistic TRC-449 schematics should be pretty close

D12 and D22 replace with a 1N914 Diode

https://web.archive.org/web/2016110...trc_449/graphics/realistic_trc_449_sm_sch.pdf


Hope this helps
Tecnicoloco

 

[Robalo]

thank you tecnicoloco i have trc-449 service manual

 

[Robalo]

TRC-458 SERVICE MANUAL

 

[Robalo]

TRC-449 SERVICE MANUAL AND SCHEMATIC

 

[Robalo]

PC-176AA. PC-196AA. PC-353BA. Cobra 138xlr, President grant , and TRC-449

 

[Robalo]

What is those diode for on L3 to ground ?

 

[Dmans]

Robalo,
I suspect the attached is the reason for the diodes you see.

73
David

 

[Handy Andy]

@Robalo - this too might help...

It's a little history on what that "mod" is...

Only it really isn't...

It's input protection for ANY RF receivers' front end RF amp.

It was not always included in many Radios because they never imagined the issue of RFI and EMP spikes doing damage to a radios RF amp - the signal reception is so small, but they didn't figure the amp needed input protection from overload of other types that are from Static discharge from Lightning onto EMP from man-made sources.

They did put some type of Recirculating Current Shunt in nearly all their radios...

Even the lowly Cobra 19 PLUS...


But Not all...
The Cobra 138 XLR
​

 

[Robalo]

L3 wrong schematic and the L4 mod. It work great for me.

 

[Handy Andy]

Just showing the older schematics from the Manuals - they too did not have the Diode mod...even the 138XLR

 

[Dmans]

I just put the covers back on my 138XLR (I don't think they have ever been removed). It does not have the diode mod on L3.
Just checking it out since I have not powered it up since getting it. Needs a recap and alignment but is right now listening to South American skip but does not have an L6 coil or FT2 filter in it (yet!). This one will be a keeper!!

73
David

 

[Robalo]

have an L6 coil or FT2 filter

the president GRANT IT does have the filter.
check this video

 

[Dmans]

Did that modification to my 139XLR-it works. I will do it to the 138 during the recap as well as adding 2-FT2 filters in series (thanks Unit_399). This works VERY WELL!!

73
David