A Pair of Tek 2465s

[mawyatt]

Hello,

Awhile back I purchased a Tektronix 2465 off eBay, only to discover shipping damage (very poorly packed), and a host of other problems. Earlier I had ordered a Tek 2445 and had the PS burn up after a couple hours use (0.068uF film cap shorted and exploded which burnt up a 68 ohm resistor). So not much luck for starters!!

Kept the 2465 but the 2445 (really messy from cap explosion and resistor burning) went back. After fixing the mechanical issues with the 2465, went on to the electrical issues. Decided to recap the scope (after seeing a couple PS caps leaking) and ordered the caps that we didn't have, most of the caps in power supply were replaced initially. Then on to fixing the Calibrator, which was traced to a defective Zener diode.

In the meantime another 2465 was acquired off eBay (hopefully getting one really good 2465 from both), this one end up having input problems on Channel 1 and 2. Basically Input Ground, nor 50 Ohms didn't work, and the other settings were highly intermittent, traced to the the input attenuator hybrid modules & relays. Replacing these is expensive, so we ended up disassembling the hybrids and carefully cleaning the open air relay contact areas on the hybrids and contact pad feet (probably tobacco smoke damage and film residue). Reassembling the scope and the attenuator worked, but other problems arrived!! Checked to power supply voltages at the main board and one voltage was way off, but on the power supply was OK. Sure enough one of the pins on the power supply cable had broken, decided to solder the wires directly to the main board. This worked and the scope was back to life, but some of the power supply caps looked like they needed replacing and the mains 0.068uF film caps looked like they were ready to blow.

Finally the replacement caps arrived and the 2snd 2465 scope had all the power supply and other circuits electrolytic caps and most film caps replaced. The switch for the beam finder was broken and the mains power switch was also found to be broken. These were found when the large main PCB was removed for recaping, super glue partially fixed the power supply switch but the beam finder was unrepairable. When the scope was reassembled the scope display was all messed up, this looked like what the display is when the beam finder is pushed. Some circuit tracing reveled that the beam finder function is active when high and the switch contacts are normally closed, shorting the function to ground. A shorting jumper across the remains of the beam finder switch permanently disables the beam finder and the scope now works. Very clean and crisp trace display and text 

Now for the 1st 2465, replaced the remaining electrolytic caps on the various boards and put things back together. No text and the display is fuzzy and really messed up, much different than the beam finder display. After carefully checking every cap to make sure everything was done correctly, still no progress. All supply voltages measured good, with very little noise. Over a period of 3 days troubleshooting and such, even swapping out the channel select U400 module, nothing was pointing to what was the problem. The troubleshoot manual guide wasn't much help either. So began to study the schematics in detail and found that the drive signals to the vertical CRT pins are dual pairs current in and out. These were suspect areas as the traces were not correct. Evidently the hybrid vertical output module U600 the outputs are differential open collector and sink currents thru the CRT vertical coils, the load impedance is partially obtained, with supply voltage from the small PCB that sits on top of the CRT. A small single pin connector supplies this PCB with 42 volts from the HV power supply PCB.

The pin had slightly pulled loose from the 1 pin connector, but looked OK. Reinsert the connector and now 42 volts was applied and everything worked!!! Took 3 days to find this

To better secure this loose 1 pin connector, added a small stripe of tape.

Now have 2 restored and recapped Tek 2465 scopes, both with clear and crisp traces and text

Anyway, hope this helps some folks with troubleshooting these scopes. Lots of work getting them back in working order and such, but worth the effort and beautiful instruments indeed 

Best,

Mike

[tggzzz]

Congratulations, and you are now an honourary member of the TEA thread https://www.eevblog.com/forum/testgear/test-equipment-anonymous-(tea)-group-therapy-thread/ The denizens are friendly, even if they we do witter on about some non-TEA topics.

The "film caps" are usually referred to as RIFAs. I've had two RIFAs detonate, once in the first 2465 I bought, and again tonight in another 2465DMS

RIFAs are notorious "delayed action smoke generators". You should always replace them whereever you find them, especially if the surface is crazed. They can also be hidden inside IEC mains connectors with integral filtering.

[mawyatt]

Thanks.

One of those large RIFA film caps looked ready to go, the other was also bulging. A few of the silver electrolytic caps were leaking too, so probably got all these just in time

Noted the traces and text were more crisp after the recap, so suspect that some of the PS ripple was causing some fuzziness.

Any recommendations for some good cheap scope probes? Have a couple of the P6100 but they are intermittent, maybe should get some old Tek probes off eBay and roll the dice 

Best,

Mike

[tggzzz]

These are my RIFAs, as extracted today...

As for probes, good probes aren't cheap. Digikey sell some for >£5k, and they are not the most expensive!

So:

• define what you need them to do, particularly w.r.t. safety. The refs at https://entertaininghacks.wordpress.com/library-2/scope-probe-reference-material/ might help
• define what type of probe you need for that
• work out specific example

Personally I stay away from *1/*10 switchable, since sooner or later they will be in the wrong position.

A problem with old probes is the leads can be stiff or brittle.

Probably a reasonable strategy for bog-standard 100/200MHz *10 "high" <cough> impedance probes is to buy something cheap and find out what you really want! I wouldn't want to point to a specific brand, but others have commented in other threads.

[mawyatt]

Yes, just a pair of probes for standard usage, something at 100MHz or > BW. The cheap P6100s are OK, except they are intermittent, both of them. Not sure if this is common so maybe I'll just order another set and hope they aren't intermittent.

Those RIFA caps look similar, except the blown one (I'm sure one of these was about ready, as it was really expanded). Here's what the recap looked like.

Best,

Mike