SBE Trinidad III problem

[Deleted]

This is one of those I purchased cheap for repair, to help me learn about these things.

This has no receive or transmit. When I put a 27.185 at the antenna, I do not get any deflection on the meter, and only hear a small tone if I jack to amplitude to like 1 volt. I traced thru the final and pre-final stages, and they appear good.

Then I went to the PLL. The 10.240 was measuring at 30MHz with no adjust. I changed the crystal, and was able adjust, but only to 14MHz.

Any thoughts?

[Deleted]

Well, I was able to get below 10.240, but cannot get close. Drifts all over the place. 30MHz to 0MHz and everywhere in between.

[Sandbagger]

Feb 28, 2009 13:50:57 GMT -5 @vinnies said:

This is one of those I purchased cheap for repair, to help me learn about these things.

This has no receive or transmit. When I put a 27.185 at the antenna, I do not get any deflection on the meter, and only hear a small tone if I jack to amplitude to like 1 volt. I traced thru the final and pre-final stages, and they appear good.

Then I went to the PLL. The 10.240 was measuring at 30MHz with no adjust. I changed the crystal, and was able adjust, but only to 14MHz.

Any thoughts?

Man, you always seem to get mired in those problem radios......

I also think you're getting confused by your freq counter triggering on harmonics of the desired frequency. Some counters will read high and unstable frequencies if the signal sample level is not high enough. The 10.24 Mhz is the reference frequency. It should be good enough for now to see that the signal is there, which you can do with a decent scope. Then I would check the VCO output to see if the frequency is correct and changes with the channel selector. You can also look at the unlock pin on the PLL to see if it's in a locked condition. If in an unlock condition (I don't know offhand if that radio's PLL chip uses a logic low or high for the unlock state), the radio won't transmit, and the PLL has a problem. You can then see if the VCO control voltage is stuck high or low, and whether adjusting the VCO oscillator coil can vary the voltage. If there's a PLL problem, there are a multitude of things that can go wrong. I was not able to find a schematic on the Trinidad III, so I can't really be of any more specific help at this point.
Of course this is also assuming that all of your power supply voltages are correct. That should be the very first thing you check.

[Deleted]

You have no idead how frustrationg this is. I have 3 radios I purchased broken. This SBE, the Robyn, and a Cobra 139XLR. I did this to learn. The thing that aggrivates me is that I have fixed a ton of other radios for friends, like Colt 1000, Cobra 1000, Washington (2 other techs couldn't fix it), Tram D201A, etc. Then when it comes to mine, I cannot fix them.

I don't think I am readiing harmonics, and the PLL alightment procedure asks to adjust L1 during transmit at 10.238, and then a trim pot on receive for 10.240. The transmt adjust is reading 10.233, and won't adjust either way. So think the freq counter it working correctly. The PLL is the MC14568/MC14526. The trim pot will vary the freq but all over the place, and if I to too far, it reads all zeros. If I go too far the other way, it reads 30MHz. Anything in between is unstable. I cannot get close. I checked the components in the oscillator, and they are all good. The sad thing is this radio is about mint. It looked like it got little usage during the fad, and sat on a shelf for 30 years.

[Sandbagger]

Feb 28, 2009 20:37:57 GMT -5 @vinnies said:

You have no idead how frustrationg this is. I have 3 radios I purchased broken. This SBE, the Robyn, and a Cobra 139XLR. I did this to learn. The thing that aggrivates me is that I have fixed a ton of other radios for friends, like Colt 1000, Cobra 1000, Washington (2 other techs couldn't fix it), Tram D201A, etc. Then when it comes to mine, I cannot fix them.

I don't think I am readiing harmonics, and the PLL alightment procedure asks to adjust L1 during transmit at 10.238, and then a trim pot on receive for 10.240. The transmt adjust is reading 10.233, and won't adjust either way. So think the freq counter it working correctly. The PLL is the MC14568/MC14526. The trim pot will vary the freq but all over the place, and if I to too far, it reads all zeros. If I go too far the other way, it reads 30MHz. Anything in between is unstable. I cannot get close. I checked the components in the oscillator, and they are all good. The sad thing is this radio is about mint. It looked like it got little usage during the fad, and sat on a shelf for 30 years.

It's possible that the radio developed the problem 30 years ago, and was put on the shelf..... That's why it's so clean.

The reference oscillator should run at 10.240 Mhz. Shifting the offset on receive is a bit strange, but those early SBE 40 channel radios were strange. I wouldn't spend too much time worrying if the 10.24 oscillator is exact. The frequency is not critical for it to work. You need to get the schematic and block diagram and check the VCO and associated mixer oscillators and see if they're working. I'll try to find the schematic again and I might be able to give you more specific help.

[Deleted]

I would think you are right with the problem developing 30 years ago. When the frequency is pegged in the other direction, it 30.706 MHz, which is nearly triple, but not quite. Not sure what is going on, as every PLL I aligned before has always measures correctly on my frequecny counter.

Regard the alignment steps, the Sams book states:

1. L1 for 10.238 on transmit (stuck at 10.233)
2. Trim pot for 10.240 on receive (0-30.706MHz and everything in between)

That is a bit odd.