Tektronix AWG2021 Repair

[OsciX]

Hello, I have recently purchased a Tek AWG2021 off of Ebay for $140. It has the rackmount option (which I quickly took off) and is covered in thick black dust!
I cleaned the outside, and took a look inside, in hopes of fixing the FAIL 650 that the Ch1 and Ch2 are throwing on setup.

The manual has helped me narrow this down to the two "A3/A23 Analog Boards" inside the unit. A cursory inspection and they look clean, nothing obviously wrong. I sprayed off some of the dust and it is still throwing the error. (I plan to clean it better once I take the boards out.) Does anybody have any advice before I start probing voltages and checking capacitors? This might be an involved repair, seeing as how the service manual is merely module-level... no schematics to be seen.

Additionally, from what I understand, the display is having some "convergence" issues. I'm aware of CRT safety practices, but how should I go about adjusting this?

[nctnico]

See the small cylindrical electrolytics? Replace all of them and clean the board thouroughly using simple green and after that alcohol. If you are lucky, the electrolyte is causing a short somewhere. If you are unlucky, you have to hunt for broken tracks / vias.

'Convergence' problem can be a power supply issue so check the power suply rails first. This isn't a convergence problem though but a vertical deflection issue. It could also be a defective vertical deflection amplifier. These typically don't run from high voltages.

[OsciX]

Got it, thank you very much! Since both of the boards are throwing the same error, I'm going to start with checking the voltages they each receive, as described in the service manual. They provide a few troubleshooting steps, but go no farther... if I'm very lucky, maybe it's one of the rails that's dead. I'll make sure to check the voltages for the deflection while I'm in there -- I see this CRT is a Toshiba unit, so I can hunt around for specific documentation for it if necessary.

[OsciX]

"Secondary Power Supply Voltages" on the A3/A23 header J500 are all within specification, but I did notice during my bench testing that the fan does not come on as described in the procedure. Maybe there's another root cause within the power supply. I'll investigate before I put my capacitor order in.

[coromonadalix]

I disagree, dont change parts until you are sure its the problem

Thes types of aluminum caps are more stable than you think, sure they are not eternals ...

But dont change parts for fun,  and theses normally require a good soldering skill to remove, or remove them by hot air

You can damage the pcb pads

[OsciX]

Not replacing parts ended up being a good move. After futher research last night, FAIL[650] was caused by a dead cal battery. Letting it run its self checks alleviates the problem until it is unplugged. The fan was also just unplugged out of the header... I'm not sure that was such a bright idea in an industrial environment, as the thing radiates heat.

Now, the only remaining problem is the CRT, and I have a prime suspect for that, too. Do you think the VPOSI adjustment potentiometer just spinning could cause this? If it's open, and VPOSI stands for Vertical POSItion, I think I might have a culprit. It's a start, at least. Particularly of note is that the CRT is sensitive to changes in gravity: when I flip the unit upside down, the alignment changes.

[nctnico]

I disagree, dont change parts until you are sure its the problem

Thes types of aluminum caps are more stable than you think, sure they are not eternals ...

Normally I strongly agree not to change parts but in this case not. Tektronix has had a huge badge of bad electrolytic capacitors they used in the early 90's. These will leak and cause a lot of damage if not replaced. The tell-tale sign is a greasy circle around the capacitor due to electrolyte leaking out. However after looking at the date codes, this unit seems to be a later model from around 97 / 98 which should be OK.

[OsciX]

It seems as if both the VPOSI and VLIN potentiometers are acting up, so I figured I would replace them all. Later models of this subassembly I see online have the parts swapped, so it might have been an ECO. Does anybody know what this trim pot form factor is called? Most of the values seem to be identifiable -- E.G., 224 -- but one of them says "23U" or 23Li" in blue text. Any guesses on what that value could be? I can always measure most of them, but I'd just like to confirm.

[coromonadalix]

check for writings on the blue part of the pot,  we see an 10k  on one of them

where you put an screw driver


normally called vertical mount trimpots, or some used triangular shaped trimpot ...

Examples
https://www.allelectronics.com/category/470100/potentiometers/trimmer-potentiometers/1.html

[OsciX]

I looked around and these appear to be ancient TE Connectivity Type 416 potentiometers. I desoldered them all and measured, but none of the markings make sense, maybe they have degraded.  These potentiometers have a 50 turn lifespan, which may have contributed to their failure. I'm sure the thick, black dust did them no favors. I've attached the full list of measurements for posterity.

I'm replacing them all with Bourns 3362S parts, selected because they have the same lead spacing type. It's very hard to find these values in 6mm potentiometers, so I compromised on the 200-turn lifespan. They're sealed, and have a much better tolerance, so they should last a good deal longer no matter what.

[Repairguy42]

Hello Group,
I also have an AWG 2021 I purchased from Ebay, actually I have two, both are two channel. One works fine but the case and face plate are a bit banged up (Unit1). Both units are pretty clean inside.
The second one is reporting "Trigger Fail 810" on start diagnostics (Unit2). That one had an (A25) Digital TTL Data Output option installed.
I removed the (A25) thinking it may be cause & I don't really need it anyway. That resulted in no change.
Then I interchanged Both "A3" and "A23" channel modules between the two units and fault did not move with them.
Then I also swapped Power Supply Modules (A4) and fault did not change.
I was going to swap the "A21" (Ch-1) and "A31" (CH-2) cards but they seem to be quite different between units.
The A21/31 modules in the problem unit each consist of two stacked cards. The good unit's A21/31 cards are each single cards.
Would be grateful for suggestions.

[Repairguy42]

I've got an AWG2021 I bought on Ebay. It is giving trigger fail "810" on second channel at power on diagnostics. I have a second unit which works fine so could fortunately board-swap-troubleshoot. Service manual did not help locate problem. Finally was able to isolate problem to the "Synthesizer Board A10", after trying all other boards.
PN/ 671-3459-00
      389-A371-00
There is no visible issue and I did replace many of the SMD mount electrotytic caps as they are from late 90's.
I have not removed the RF-cages to get at the "SERIAL INPUT PLL FREQUENCY SYNTHESIZER WITH 520MHz PRESCALER {Fujitsu MB1504H}
The RF-Cage looks like a bear to get off.
Would like to repair board or find a replacement but parts are pretty slim for these.
The working 2 channel AWG2021 is a really nice tool and at today's prices such products cost ++

[OsciX]

RepairGuy42, I just got mine working. It turned out to be the CRT potentiometers and the calibration battery.
The CRT still looks a tiny bit off in terms of scale, but barely noticeable... definitely super usable. Were you able to make any progress on yours? I'll try to help if I can.

It appears that ERR 810 and 811 are a fault of the A4 power board according to the Service Manual, Figure 6-39. Were you able to measure the voltages mentioned in Table 6-5?
This is just a guess -- if you've narrowed it down with your replacements instead, forgive me. Does the unit under test work with a replacement A10 board?