Realistic TRC457 Alignment Issues

[ira parker]

PC-196BD I have several issues with this one? History, recapped it using [EL CAPO (399) RIP] list for upgrades, d-23 replacement, c179 swap from tantalum, removed channel mod, did a modified variable dead key following Nomads version (I use a fixed resistor for dead key instead of the variable pot), replaced driver and final 2166-1969. Pll and vco took alignment just fine all 3 bands spot on frequency rx/tx. Tuned rx section all good. Tuned tx section on channel 20 am, 2 watt dead key swings 16 watts peak flipped to ssb was only seeing 6 watts peak? So I retuned tx in ssb came up to 18 watts peak, went back to am dead key was 1 watt swings 8 peak? (Is this normal) I can split the difference on the tx chain alignment between am and ssb to get about 12-13 watts peak which I am fine with. Just didn't know if I was missing something in the alignment procedure to balance the output between the bands or if I have another issue to look for? Sooooo going thru the channels I find that about channel 28 the dead key and peak power starting to drop by the time I get to channel 40 the dead key is back to 1.25 watt peaking 6-7 watts both am and ssb (what the hell) I didn't think these 858 boards were this narrow banded on normal 40 channels. I know that you have to broad band L4 and L37 sometimes with a channel mod, (which I would like to put the uppers back in it) so I went to channel 40 retuned tx balancing between am and ssb it will only peak 9 watts on both. Any help/thoughts suggestions etc. now on to issue #2

Omron relay issues it works as it should butt it will drop receive intermittently, I can lightly tap the relay and rx returns I've cleaned them with a piece of paper and solvent. (I've got 3 relays that all do the same thing) I removed the quick disconnect socket went to direct soldered install inspected all surrounding components for cold solder joints good continuity everywhere. I'm not a fan of burnishing contacts but on this older relay would it be acceptable with some 4000 grit and a light clean up. Or does anybody have a mod to upgrade the relay to somewhat newer style? I've got a few more but don't want to remove them from working radios. On to #3

The channel mod that was in here is a spdt switch pin #19 isolated from ground wire to center leg of switch bottom of switch to ground top of switch to pin #7 ? Switch up grounds pin #19 normal channels 1 thru 40, switch down channel 1 is 26.565 channel 40 is 27.805 didn't check all channels removed the mod until i get the rest of it sorted out, grounded pin #19 for normal channels. I haven't seen channel mods on this chip done that way? My thoughts on this are to isolate pin #19 from ground add the 4.7k resistor to ground from pin #19 and the wire to center leg of spdt switch, bottom leg of switch to ground for normal 40 channels top leg of switch to pin #21. Not sure of what frequencies it will go to. Got this mod off of cb tricks but it didn't show the bottom pin going to ground just the center leg to pin #19 resistor to ground top leg to pin #21 I'm assuming the ground for pin #19 on bottom leg for normal 40 the schematic on cb tricks didn't show it but I think they were just showing the channel expansion. Thoughts/suggestion ect. Sorry about the long post but the more info I can give the hopefully the better understanding on the forums side of it. As always Thanks for the knowledge and input this forum has created.

Thanks Ira

 

[ira parker]

Never mind on issue #2. Rolled the dice light burnishing with 4000 grit and they seem to be holding fine.

Thanks Ira

 

[TM86]

The upd858 pll is a bit weird in that it uses Binary Coded Decimal (BCD) instead of straight binary for setting the channel. When you've got pins 19 and 20 both set high at the same time, it gives an "illegal" code of 12 in the BCD world, where the highest number for a set of four pins is always 9. That's why your radio dropped below channel 1 on the first seven or so channel positions.

It is, of course, a bit more complicated than that, involving thinking in terms of "ones", "tens', and "hundreds". But that's the gist of it.

If you tie pin 19 to pin 21 like you've suggested you should get pretty much the same set of upper frequencies from 8 on up as you had with the original mod, and normal channels on 1-7.

Also, I think the reason the original mod attached to pin 7 is because it was a convenient source of +5v that happened to be nearby. That pin sets whether the chip is using 10kHz or 5kHz spacing, with 10kHz selected when a voltage is applied and 5kHz when grounded.

 

[ira parker]

Thanks TM86, I hadn't seen a channel mod using pin #7 or isolation of pin #19 without the resistor to ground. The 12 count on the binary makes sense on the confusing freqs on 1-7. The mod in the realistic section on cb tricks made more sense to me but was a little short on the schematic. So when I reinstall the the channel mod that's the one I'll use. Once again really appreciate the input.

Thanks Ira