Gigatronics 6100 Repair

[Nitrousoxide]

Hi all,

I recently acquired a Gigatronics 6100 2Ghz to 8Ghz frequency synthesizer. It did turn on for the first few times, and then after a while proceeded to stop functioning (it turns on, but sits in some sort of locked up state with the VFD partially lit, LED display not lit). When it did work, it would fail the self test (throwing an error 0/PLL error).

Im starting a thread as there seems to be little to no information online in terms of service manuals. Ill document the steps I take just in case someone else comes across this in need.

Photo of the inside:



So two questions to start off:

By any chance does anyone have, or know where to get service manuals for the 6100?

The inside consists of cards (see picture). Some of the cards are well and truly stuck inside the slots, and I'm not afraid to use a bit of force... but even when I did they didn't budge at all. Does anyone have any tips as how to free stuck cards?

[dacman]

What I would use for the stuck cards is a little LPS-1 (a lubricant I use for electronics).

Do the cards have holes that could be used with a card puller?  One could be made out of an old clothes hanger with a thread spool for a handle.  It should connect to the card at two places in order to distribute force evenly.

[Nitrousoxide]

What I would use for the stuck cards is a little LPS-1 (a lubricant I use for electronics).

Do the cards have holes that could be used with a card puller?  One could be made out of an old clothes hanger with a thread spool for a handle.  It should connect to the card at two places in order to distribute force evenly.

Yes they have holes. Ive attempted to shimmy cards out by one side at a time, but I will try your homebew suggestion.

I cant seem to source LPS-1. However, as it seems like a generic spray on lubrican, I'm going too see if I can source one locally that isnt agressive and is non conductive.

Another statement I should make is that the device did power on (boot) before I opened the lid. The only difference I could tell was pressure being placed on the cards. I tried putting the lid back on but to no avail it would not boot. At that time the only change I had made was taking the lid on an off, not even touching any cards. However, there does seem to be some form of degrading RF gasket that crumbles away on touch. Its non conductive at DC, however, I wouldnt trust it. Im going to suck away all the crumbs and the remaining,

[Nitrousoxide]

I think I can declare this repair not worth the financial investment or time from this point on...

I didn't connect the correlation at the time. But when I had taken the top of the case off, the unit ceased to work even once placing the case together again. Pulling the cards to visually inspect them I see a UV erasable EPROM (am27c64-150dc) which was not visible from the top view of all the cards 

There is another card that contains ROM chips that I assume holds the majority of the software, however, Its probably safe to assume that this ROM chip held some form of bootloader that has now vanished.

I find it a bit odd since there was nothing covering the window... Wouldn't stray UV light slowly degrade the bits inside the memory? The card wasn't placed in any form of light trap.

What excellent design . Id assume there's absolutely no way of recovery.

EDIT: I wouldn't call it a total loss... The RF modules inside are significantly derated and would make a nice addition to my arsenal.

EDIT2: It lives! (Kinda). The VFD and half the front panel do not work. I assume reseating cards will possibly resurrect this issue.

[wulfman]

It takes a LOT of UV to erase an eprom, just missing a label wont kill them especially inside the case.
Be sure to look for a battery. some times batteries leak and cause corrosion.

[Berni]

I have two Gigatronics RF Synthesizers and a service manual for a similar model in dead tree form. Yes it is difficult to come across service manuals for these things online.

A EPROM wouldn't get erased so easily inside a case unless it was in a location close to a vent and the unit was sitting in direct sunlight for years or something. For ROM chips gear doesn't usually even have capability to write to them at all. My guess is that the ROMs hold the firmware and  the EPROM holds the calibration data.

So far the problem sounds like it could still be a simple power supply or bad contact issue.

[Nitrousoxide]

So far the problem sounds like it could still be a simple power supply or bad contact issue.

You were exactly correct. Reseating all the boards have returned it to working order. However, the previous owner had neglected it and left it where moisture could get to it (probably a garage). Additionally, most of the electrolytic caps for the VFD and front panel have completely leaked. I have replaced then and all seems well.

However, there is still the main issue as to why I originally had opened the unit up. It is still throwing me an ERROR 0/PLL. I can see one red LED vaguely lit when in the lower frequency region of the device. I will remove the cards and visually inspect them all for more leaking capacitors.

[Berni]

Ah glad you got it running again.

Be sure to clean the area around those capacitors since the electrolyte is nasty stuff for PCB traces and it can be hard to see. On more modern boards with green solder mask you can see the damage from leaking capacitors by shinning a UV light at the board, it glows differently around leaking caps.

The PLL issue sounds potentially a bit more serious, but given that corrosion and bad caps ware found its a good bet they are elsewhere too.

[Nitrousoxide]

Ah glad you got it running again.

Be sure to clean the area around those capacitors since the electrolyte is nasty stuff for PCB traces and it can be hard to see. On more modern boards with green solder mask you can see the damage from leaking capacitors by shinning a UV light at the board, it glows differently around leaking caps.

The PLL issue sounds potentially a bit more serious, but given that corrosion and bad caps ware found its a good bet they are elsewhere too.

Yeah. Ive pulled all the cards now and have labels for them:

A0: "KEY BD VIA"
A1: "VIA"
A2: "MEMORY"
A3: "IEEE "
A4: "CPU"
A5: "LEVEL CONTROL"
A6: "Output PLL"
A7: "40-80MHZ"
A8: "40-80 MHZ PLL"
A9: "INTERMEDIATE PLL"
A10: "HI RESOLUTION"
A11: "300 MHZ PLL"
A12: "110 MHZ REF PLL"
A13: "YIG DRIVER"
A14: "Mod Control D/A"
A15: "Sig Gen"
A16: EMPTY
A17: "Digital Pulse Generator"
A18: "Driver"

Issue is, as you can see there are multiple PLL's so I'm not too sure which one the error is referring to. I can see the output PLL led dimly flicker sometimes, so Im going to ASSUME (bad idea) that it is the board in question. However, upon visual inspection of the board (infact, all the boards) show no leaking from any capacitors.

Would it be possible for you to peruse your dead tree to see what PLL error 0 indicates?

EDIT: I've been assuming that the message is "ERROR 0/PLL". However, by using my brain it makes more sense that it is "ERROR O/PLL". Which probably means "ERROR Output PLL".

I've replaced all the electrolytics on the board and still no fix. The board consists of 6x op amps, a differential line receiver, a cmos SPST switch and a heatsunk part (which I assume is the PLL IC?)

Output PLL board:

[Berni]

My manual turns out to be for a Gigatronics 7200. Here are pictures of the relevant pages:
https://imgur.com/a/S5TLLQc

Sorry the site rotated them according to some embedded metadata.

There are no error codes mentioned in there. But there is a troubleshooting section, tho by the looks of it the instrument is very different from a 6100 so questionable if its of any use. I also included the block diagram in case yours is similar as it may aid in understanding how it works.

The whole manual is like 10cm thick because it contains a huge pile of fold out schematics for all the boards. Pretty extensive and well made, tho the troubleshooting parts are far behind oldschool HP manuals where they would practically guide you trough a repair.

[Nitrousoxide]

There are no error codes mentioned in there. But there is a troubleshooting section, tho by the looks of it the instrument is very different from a 6100 so questionable if its of any use. I also included the block diagram in case yours is similar as it may aid in understanding how it works.

Yeah, does seem quite different from a glance. Thank you so much anyway, ill give it a read.

I really didnt want to blindly start replacing components, but that's what I might have to do (beginning with all the poly/tant caps). My theory is that there must be an active loop filter on the board somewhere and some ESR from dried up capacitors is causing issues. I just don't have the time to reverse engineer the circuit, so shotgun approach seems best sadly.

Just an addition: No expense was spared when this thing was put together. The coax cable looming, even just for bias/supply voltages is insane!

There's even a gigatronics labeled can that only has two SMA connectors on it, connected to it by rigid coax is... itself. There is a passive part that literally connects to itself and nothing else... Seems like they didnt need it and just omitted it by not connecting it... absolutely crazy.

[Berni]

Yeah they are quite impressive units. I got a Gigatronics 6100 that goes to 8GHz and a Gigatronics 7100 that goes to 20GHz.

Id imagine the front panel also looked pretty striking back in the day. Just that green 2x10 character LED matrix display must have cost a pretty penny back in the day.(I think the 6100 has a 1x10 instead)

First thing id check are power supply rails with a scope. Also check what happens to the output in the area where the PLL goes unlocked. Does the output disappear, does it wander off in frequency or amplitude, does it become jittery or noisy etc. Perhaps you can work your way from the output connector backwards to trace where the same issue appears.

Hope you have a spectrum analyzer cause it will likely come in useful.

[Nitrousoxide]

Must admit, The LED display does look VERY nice.

With the gear I have, I think I can cove 9khz-2.7Ghz and 4-6Ghz. I suppose thats good enough to detect a signal.

Right now, just sweeping the device over its output range yeilds nothing. Absolutely no output, even in the ~5Ghz range where both lock and level lights are illuminated.

I will check the power supplies first and then if that brings me to a dead end, ill draw up my own block diagram.

The issue is, I can only really make an assumption as to what the supply rails should be as, again, no documentation

[Berni]

Well my 6100 did at one point develop a fault where it gave very little output power no matter how high you cranked up the level. This turned out to be a fault in the switched attenuator block before the output. One of the solenoids inside got stuck and kept the biggest attenuator in circuit. I found that shimming the faulty selonoid with some paper helped, might just be mechanical wear. Later on i scored a replacement attenuator module, but i haven't put it in since it might throw off the calibration.

Good luck with yours.

[Hg7wgs]

This is a gigatronics 7100. What pcb-card might it be missing? Where can I find a schematics diagram or servicemanual? Maybe i build the pcb.
Thx Szabolcs

[Stray Electron]

   Oops. Necro-thread.