Recently I picked up this wee gadget, figured it was useful for parts. Then I discovered the power supply had died, and chances are that it would actually fire up once it was repaired. Its a 1980s spectrum analyser, 100 kc all the way to 22 gigs!! It would have cost an absolute fortune in the day. Before dismantling it, decided to have a quick fault find.
First problem was the voltage regulator chips, the 5 volt at 8 amp section was faulty, as is the -18 volt. The supply is current limited via 2milliohm shunts, and overvoltage protected via SCR crowbars. These are vicious, in that when the voltage rises over a set amount, the SCRs literally will short the supply to ground, blowing all the fuses. Anyways, the supply is faulty. The 723 regulators, 4 of them are the older round can type packages with 10 leads, so nothing else will fit. I did consider building a new supply using the existing huge and heavy transformer, but its a lot of work if the thing is truly knackered. As luck would have it, Alibaba has these old chip in stock, they are on the way to me as I speak!! Thought Id post this, as I am quite excited to see if it is repairable.
If anyone has any data on this thing, Its proudly made in the US, and seems to use a lot of Hewlet Packard microwave bits, a Motorola CRT display module, these were a generic thing fitted to many devices of the era. Its a real hodgepodge of different modules. Its branded as an Eaton 757, thats whats written on the service manual I found on the internet, the brand on the SA is ETN advanced electronics.
Here are some pics in case it activates anyones memory. I have no use for it, but its a waste to dump it without trying.
Well, the ongoing saga of this analyser....
Fixed the power supply, reinstated the lost negative 18 volt rail, and bang, it destroyed itself again....
Found a shorted tantalum cap in the main unit, removed it. Repaired the power supply, the machine fired up for a few minutes before shutting down.
Suspected more shorted tants, and rather than tracking them all down, injected negative 18 volts from my high current bench supply looking for smoke.
Three more tants caught fire, removed them, now its running stably.
Next issue, no CRT display,and a no changing frequency display.
The latter was tracked down to a slipping ball drive, this connects to a very expensive looking multi turn pot, this voltage tunes the YIG oscillator through a magnetic clutch,,,, remember, this is 1982, the world of analog. Another multiturn pot is also turned via another magnetic clutch, this one is for fine tuning. This arrangement is quite clever as the rough center frequency is tuned, then deactivated , and then the other is activated to fine tune..... 100kc to 22 gigs is one big sweep!!
These YIG oscillators use negative resistance materials, the frequency is adjusted via a magnetic field, even the latest SAs use the same principal, where a large coil sets the base frequency, then the PLL pushes current through a smaller coil to lock it over a much smaller range.
Pulled this apart and recrimped the ball drive pressure tags.
The thing now tunes to 22 gigs in 5/6 bands.
Unsure why there is no CRT display, its a HP vector X/Y display that appears to have all its voltages correct. Connecting the scope in X/Y mode gives a display that is totally meaningless, but indicates we do have valid display signals going in.
The power supply runs very warm, this could be normal for this high current linear regulated supply, I dont know.
It seems unlikely this behemoth would have so many natural faults, I suspect it may have done the rounds of a few repair shops, each one adding to the problems.
So, if anyone has any experience with the HP 1340a vector graphics display, I am all ears.
For instance, will it have anything on screen with no video inputs, or remain dark? If I grounded the blanking grid to force the CRT display on, will this cause any further damage?
What are those 2 x 40 pin gold plated ceramic important looking chips doing, and what are they?
Meantime, it does appear the analyser is now working to at least a limited degree.
Looks like it cost a million dollars.😁 Good luck.
Wow, nice find.
I might have one or two genuine '723 regulators in the 10 pin can that I bought back in the 80's . I know for sure I have some of the 14 pin DIP chips.
73,
Win W5JAG