Tektronix 2465B Capacitor Replacement and Repair

Recently and randomly I was notified from a friend about a local company liquidation auction for a local Unisys facility that was shutting down. Hoping to score some cool old vintage computer hardware I scoured the item listings to no avail. Nothing was really of interest, a lot of office furniture, shelving units, misc bins of random hardware bits. Ten years ago I would have been all over this auction, bidding on random carts of hardware to see what I can find but I just don't have time or the space for that anymore. After looking at a hundred or so pages of auction photos, one thing did catch my interest.

Hiding on an equipment cart was a Tektronix 2465B, sitting all by itself, the only piece of test gear in the entire auction out of hundreds of lots. I'm sure it was dead, the odds of it working and still being there were very unlikely.  Having a 2445B, I have always wanted a 2465B, being the top of the line version at the time only second to the 2467 with its microchannel plate CRT. I ended up winning it for like 50 dollars including the cart which actually ended up being a really nice heavy duty equipment cart. Even if this scope was totally toast, it would still be a win for parts.

Once I actually picked up the scope and had a good look at it, it was in pretty good shape. The only physical damage was the vertical position knob for channel 2 being broken off, but this was visible in the auction picture. The rest of the scope was in really good condition, clean with no other physical damage.

Tektronix 2465B

Having restored my 2445B and knowing this will need a full re-cap, I ordered all the replacement caps for the power supply and A5 PCB boards. The power supply for the entire 24NN series was basically identical with a few minor revisions. One thing I did notice though was some of the capacitor values were different in this 2465B compared to the capacitor list I had for my 2445B. Instead of placing the order based on my old parts list, I created a new list based off the values in this scope. Some parts on my old DigiKey list were no longer available anyway.

Here is the updated DigiKey parts list:

Quantity	Part Number	Manufacturer Part Number	Description
10	P10267-ND	EEU-FC1E470	CAP ALUM 47UF 20% 25V RADIAL
2	P13465-ND	EEU-EB1H4R7S	CAP ALUM 4.7UF 20% 50V RADIAL
1	P5874-ND	ECA-2WHG3R3	CAP ALUM 3.3UF 20% 450V RADIAL
4	P10769-ND	EEU-FC2A100	CAP ALUM 10UF 20% 100V RADIAL
4	493-10252-1-ND	UMP1H010MDD1TP	CAP ALUM 1UF 20% 50V RADIAL
1	399-7494-ND	PME271Y510MR06	CAP FILM 10000PF 20% 1KVDC RAD
2	399-5410-ND	PME271Y422MR30	CAP FILM 2200PF 20% 1KVDC RADIAL
1	EF2563-ND	ECQ-E2563KF	CAP FILM 0.056UF 10% 250VDC RAD
2	399-7482-ND	PME271M568MR30	CAP FILM 0.068UF 20% 275VAC RAD
2	PCE3777CT-ND	EEE-FK1A330R	CAP ALUM 33UF 20% 10V SMD
2	PCE3833CT-ND	EEE-FK1V100R	CAP ALUM 10UF 20% 35V SMD
2	493-1421-ND	UVZ2E331MRD	CAP ALUM 330UF 20% 250V RADIAL
10	P10323-ND	EEU-FC1H101	CAP ALUM 100UF 20% 50V RADIAL
1	P5856-ND	ECA-2CHG100	CAP ALUM 10UF 20% 160V RADIAL
4	P11236-ND	EEU-FC1V271	CAP ALUM 270UF 20% 35V RADIAL
2	P10345-ND	EEU-FC1J181S	CAP ALUM 180UF 20% 63V RADIAL

Note that I ordered a few extra values of some of the caps to meet price breaks. Total cost came to $30.02 without shipping.

Just like on my 2445B, I always use high quality Panasonic 105 C caps and original replacement RIFA film capacitors. The couple non-polarized caps are 105 C Nichicons along with the two large filter caps. None of the resistors in this power supply were damaged like on my 2445B, so I left them alone on this one.

2465B power supply with new capacitors

For my first power on test, the scope did power up, went through the first self-test cycling the panel LEDs, fan was running, but nothing on the CRT. Intensity controls had no effect. Even the graticule illumination was dead. Timebase, channel, and trigger controls responded to changes so the digital portions were at least working. Checking voltages, some were off and had ripple so I powered down and would wait for the capacitors to arrive.

Once all capacitors were replaced, powering up had the same result as before. Checking voltages they were all in spec now and the ripple I had was gone, but still no display. Time to reference the service manual.

One note on the 2465B service manual, I found three different versions all of which having some slightly different information. None of the info contradicted itself, just some manuals had more information than others. Once of the manuals looked to be for the older version of the 2465B where the A5 pcb was not using surface mount components, this was for early serial numbers . The other two looked to be newer. I ended up referencing all three throughout the repair process.

Following the troubleshooting flowcharts in the service manual, I ended up adjusting the grid bias adjustment which when increasing did give me a working display. Traces appeared along with on-screen graphics, but they were out of focus and had horizontal artifacts across the display. Intensity controls had no effect leading me to believe it was something with the Z axis processing based on the service manual flowcharts. The primary culprit would be the U950 hybrid which handles most of the Z axis functionality.

2565B with grid bias increased

Since I did have a somewhat readable display, at this point I was able to run the self-test routine outlined in the service manual to verify the rest of the functionality. In doing this, the scope passed with no issues, so good news there. I could also check power-on hours and cycles, 15703 and 2440 respectably. About 5k more hours than my 2445B but still not a high amount compared to some 24NN's I have seen that are well over 30K hours.

At this step, having a working donor scope makes troubleshooting significantly easier. All of the hybrid ic's on the main board are identical, with exception to U600 which has a different part number.  165-2393-00 on the 2445B and 155-0237-00 on the 2465B. Reading into this, they are compatible with the exception being that the 2445B version does not have 400MHz bandwidth. So I can use it for testing if necessary, it will just limit bandwidth on the 2465B to something under 400MHz. You would not want to use this long term in the 2465B.

Pulling parts from a working donor scope is always a little scary, I could end up with two non-working scopes in the process but parts are now plentiful on eBay for reasonable money.

2445B donating hybrids to the 2465B

Swapping U950 from my 2445B to the 2465B did fix the display issue. After turning the grid bias back down, the intensity and readout intensity controls now properly function. The display has a nice clear readout and clean trace. Looking on eBay, a working tested replacement U950 is about $50 - $60 which has been ordered.

Checking the rest of the scopes functionality I did notice another problem. As I adjust the horizontal timebase, the trace will disappear after increasing it beyond 2ms. Turn it back down and the trace will reappear. This behavior repeats for all 4 channels and is Y axis independent. Applying a signal has no change on behavior. Either the built in square wave calibrator or an external signal from a signal generator, the scope will lose trigger right around 2ms then have no trace at all beyond 1ms. Changing any setting, 20mhz bw, delayed timebase, other triggering options, etc made no difference. So something is up with the horizontal timebase and / or triggering on this scope.

One first attempt was to swap out the remaining hybrid ic's from my 2445B to the 2465B to at least eliminate another one of them being a possible issue. This ended up making no difference, so the next step will be to go back to the service manual. Their is a lengthy flowchart to debug horizontal trace issues, following this will be my next step. I'll leave this for a part II of the repair.

Tektronix 2246 Repair

Last year I had talked about how I accidentally destroyed my Tektronix 2246 oscilloscope by removing the cover. There was a small dent in the metal bottom panel that while removing it had snagged a heatsink on a Motorola 151-0846-00 labeled TO-39 transistor, specifically Q702 on the A10 main board. This ended up ripping the pins out of the transistor can leaving me with a unusable scope. Unfortunately this was not a common part and trying to locate one is next to impossible. I had attempted to use a 2N3866A with no success, the scope was definitely not happy with that transistor in it, an original replacement part would be necessary.

I did ultimately find a donor board. Late last year I found a complete used replacement board on eBay for around $40 which contained both of the 151-0846-00 labeled transistors. This option was definitely cheaper than a whole parts scope and I would hate to ruin another 2246 which may be repairable just for this one transistor. Once I replaced this transistor in my 2246 it was good as new.

I want to focus the attention now to a second Tek 2246 scope that I own with its own set of troubles. I purchased another 2246 a few years ago for cheap, I think it was only around $100. This scope had a lot more use than my original one, while it was in good cosmetic shape it had some issues mostly related to old capacitors. The display was not stable, the character generated osd and cursors would jump around and upon probing the supply rails you could see there was some noise present. A re-cap would be necessary and possibly some additional caps on the A-10 main pcb if necessary.

The 2246 main power supply is pretty basic, much more simple to work on than the Tektronix 2445B power supply which I have also done. One interesting observation upon accessing it is that all of the caps look to be large axial electrolytics:

Trktronix 2446 Power Supply

The bottom of the board told a different story, and once removing a capacitor and testing it was indeed a standard radial cap with an interesting third lead out the top that wasn't connected to anything. Maybe it was designed for additional stability? I know this scope was a popular portable model so my guess it was just some additional ruggedness built into the design. Interesting regardless, at least I can replace them with standard radial caps which are much easier to source.

Replacement caps were all Panasonic 105 degree C. units which are always my first choice, then using Nichicon capacitors in cases where the Panasonic's were not available. The final rebuilt version looked like this:

Tek 2446 Power Supply Rebuild

Quite a difference in size. For good measure I also replaced all of the high voltage film capacitors on the board, many looked stressed as they did in the 2445B. I left the large primary switching capacitor alone, they are rarely every a source of trouble. Everything else looked okay.

This is where things started to get interesting. After putting everything together and powering the scope back up, I had strange display issues. The entire display was shifted left. I started looking around to see if I had missed a cable or possibly had a connector loose during the reassembly but didn't see anything obvious. This scope was working just fine before the power supply rebuild so this issue was definitely something that I caused. At this time I went to turn the scope over on its side while powered up that the display snapped back into alignment. After some more poking around I realized that if I put pressure on the chassis, twisting it just lightly I could get the display back in alignment. So it must be a bad ground, loose connector, bad solder joint, or some other mechanical failure where putting pressure on the chassis would complete whatever broken connection was occurring. It will just be a matter of tracing down where the issue is at. More to come in part II.

Tektronix 2445B Capacitor Replacement

Due to the fact that my Tektronix 2246 is currently out of commission (although parts are on the way as I did find a parts unit 2246 scope) I have focused my attention to my other favorite Tektronix scope, the 2445B. I primarily use my 2246 as it was the first 'real' scope I purchased about 10 years ago and is a rock solid analog scope. A few years back I came across a 2445B for a good price and have used it mostly for portable use as it is slightly smaller than my 2246. My 2445B also has Tektronix calibration stickers intact from 2002 indicating at least that no one has been inside mucking around with it.

My specific 2445B is the 150Mhz version and is in excellent condition although there have always been a few issues. The on screen display would jump around and not have a clear focus regardless of the focus adjustment and other internal astig calibration controls. When changing volts or time functions there would also be erratic display behavior. Knowing that the scope was over 20 years old and has unknown operational hours, I decided to start with a full capacitor replacement of the power supply. Electrolytic capacitors do go bad over time from several factors, so replacing them is a common step in all old electronic equipment.

The first step is to take it apart and inspect it. I will say the 2445B is one of the better scope designs I have worked on from Tektronix. The design is very modular with the power supply being very easy to access. Once removed, the power supply pulled apart into two boards shown here:

Tektronix 2445B Power Supply

There are quite a few caps between the two boards, luckily most are radial caps and not axial. As I began inspecting the caps themselves I was surprised to see that some were rated for only 85 Degrees C instead of the higher 105 Degrees C rating. I also noticed that some were definitely showing some 'bulging' which is usually indicative of high heat and ultimate failure, although none were leaking. Some other things I noticed were that all of the high voltage film capacitors looked stressed. They had slightly bulged as well and had crack marks on their casings. A few resistors also looked bad including two 15 Ohm ones within the surge protection circuitry in the line level input stage. One had actually blow open and had a physical crack in it.

Additionally looking at the A5 Control pcb I noticed that there were four surface mount electrolytic capacitors on it. I learned how leaky these caps can be after a complete Tek TDS-420 restoration which needed a total of about 75 of them replaced. Looking closely at the board I could already see they were leaking and causing corrosion to traces, so they would be replaced as well.

Tek 2445B A5 Control PCB Caps

Ultimately I decided to replace every capacitor on the power supply boards and the four smd caps on the control pcb. I would leave the caps on the A1 main pcb alone for now as they are primarily low voltage and would be considerably more work to replace. If there was still issues post-recap I would then consider replacing them as well.

For electrolytic capacitors I always go with Panasonic 105 Degrees C units. I will use Nichicon 105 C unit if a Panasonic value is not available. The film capacitors were replaced with Kemet units which were actually also the originally spec'd components. I upped the blown 15 ohm resistors to 3W units. For those interested in re-capping their own Tek 2445B (or variants) here is my Digikey parts list:

Quantity	Part Number	Description
6	P13476-ND	CAP ALUM 100UF 25V 20% RADIAL
2	P13125-ND	CAP ALUM 47UF 25V 20% RADIAL
4	P13123-ND	CAP ALUM 330UF 25V 20% RADIAL
2	P13131-ND	CAP ALUM 220UF 50V 20% RADIAL
1	P13465-ND	CAP ALUM 4.7UF 50V 20% RADIAL
1	P5874-ND	CAP ALUM 3.3UF 450V 20% RADIAL
4	P10769-ND	CAP ALUM 10UF 100V 20% RADIAL
4	493-10252-1-ND	CAP ALUM 1UF 50V 20% RADIAL
2	P15W-3BK-ND	RES 15 OHM 3W 5% AXIAL
1	989-1206-1-ND	RES 270K OHM 3W 1% AXIAL
2	P4639-ND	CAP FILM 0.068UF 250VAC RADIAL
1	399-7494-ND	CAP FILM 10000PF 250VAC RADIAL
2	399-5410-ND	CAP FILM 2200PF 250VAC RADIAL
1	EF2563-ND	CAP FILM 0.056UF 250VDC RADIAL
2	UKL1E101KPDANA-ND	CAP ALUM 100UF 25V 10% RADIAL
2	PCE3777CT-ND	CAP ALUM 33UF 10V 20% SMD
2	PCE3833CT-ND	CAP ALUM 10UF 35V 20% SMD
2	493-1421-ND	CAP ALUM 330UF 250V 20% RADIAL

Most of the Tektronix 24NN family (2445, 2455, 2465, 2467, etc) has the exact same power supply, so the component list above should apply to all. Here are the rebuilt power supplies once all components arrived:

Tek 2445B Capacitor Replacement

Once completed there were about 45 components in total that needed to be replaced. While the large Sprague 290uF caps were probably were fine I replaced them for good measure anyway.

Tek 2445B Capacitors

All completed and reassembled my 2445B has a beautiful display and extremely sharp digital readouts. I don't see any need to replace the A1 pcb caps at this time but will still consider it for the future. With a total component cost of $31 and about two hours of time I would recommend this rebuild for any original 24NN scope.

Rebuilt Tektronix 2445B

How I Accidentally Destroyed my Tektronix 2246

I have talked many times about my Tektronix 2246 oscilloscope in the past as it is by far my favorite analog scope. Simple, reliable, and inexpensive and was the first 'real' scope I had purchased used about 10 years ago. So to destroy it, all I had to do was take the enclosure off.

All Tektronix scopes of this era usually have handles attached to them for portability which is a nice feature. My problem was that I never take it anywhere, it stays firmly situated in the center on my bench as it is my go-to scope for most basic troubleshooting. Having the handle attached resulted in one problem, it prevents you from easily stacking anything else on top of it. With an ever growing bench of test equipment I really needed the real estate on top of it, so the handle had to go.

Removing the handle requires unfortunately more work than necessary. There is no external bolts to remove to take it off, instead the bolts attaching it are on the inside requiring the entire enclosure to be removed. While somewhat annoying, the handle has a well designed strong attachment to the scope. If I were to transport my scope around I would have no concerns of the handles integrity.

Tektronix 2246 Handle Mount Inside the Enclosure

Normally the covers of all scopes in this era come off easily, typically there are 4 screws on the back of the scope and maybe one or two on the sides. Once removed the back then falls off and the entire cover slides off the back. Normally I place the scope standing vertically and lift it straight up via the faceplate while the cover then remains on the bench. My Tektronix 2246, 2445B, and TDS-420 all have this very similar design (and have removed the later two without consequence).

So what went wrong? There was unfortunately a few dents on the bottom of the units case that I did not consider to be an issue. When I began sliding the cover off, it slid about 6" or so and had some resistance. Not seeing anything to be a problem I pulled a little harder (not excessively) and the cover did continue to come off as normal. Once removed I saw a small round heatsink laying on the bench. That's odd I thought, as I don't recall hearing anything rattling around inside previously. Once I looked to see where it came from I realized what had happened.

The dents on the cover that were pushed in had snagged a transistors heatsink on the bottom pcb. This had then put force on a TO-39 transistor ripping one of the leads off of it.

The transistor itself was not salvageable as the missing lead had been physically torn out of the can. Looking into the part itself it looks to not be an easy replacement. The markings on it reference it to a custom Motorola / Tektronix part number of 151-0846-00.

Searching for this part I discovered two things. 1. I'm not the first person who this has happened to. 2. There are no easy to find replacements for this part. The part is critical to the scopes operation as it will not power up without it in place.

The part cross references to a SRF5286 or 2N3866A. The 2N3866A is possible to find and purchase inexpensively, but reports from others say that since it is not an exact replacement for the original Motorola part, it will not work. I'll probably give it a try anyway and also be looking for a 2246 parts unit in the meantime. 

Harmon Kardon A300 capacitor replacement

After almost a month of listening to my new tube amp there was one slight problem I began to notice. The right channel seemed to be a little bit louder than the left. The problem seemed to get worse the more I listened to it. Or maybe I never realized it and now that I have, I listen FOR it which makes it more apparent. Either way... after a lot of checking, swapping channels of signal sources, switching speakers, etc... the right channel was louder than the left.

I figured I had three possible causes of the problem. A single or several bad/weak tubes, an out of tolerance resistor, or a bad capacitor. I started with the tubes. I swapped the 6V6GT power pentodes to see if the louder channel swapped, which it did not. I moved the 12ax7 triodes around as well, with no difference in channels. There was really nothing more i could do without a tube tester (which I find myself needing). But for now I'll assume that the tubes are ok.

Next step will be the capacitors... which I wanted to replace anyway. Lots of browsing websites of tube amp builders and repairers turned up a ridiculous amount of information about the best capacitors to use for an amp. Lots of people recommend things called "orange drops" which provide the best 'classic' sound . Whether this was the technical name of the caps or a description of what they looked like, Digi-Key turned up zero results for 'orange drops'. Now on to the more scientific approach. This site provided me good information on the linearity of different types of capacitors. After looking at this data, it looks like most capacitors would be well suited replacements with the exception of a few(ceramic disc, tantalum, etc...). I purchased high quality Panasonic polyester film capacitors for the signal paths and ordered high quality Panasonic 105 degree C. electrolytics for the power supply filtering while I was ordering parts. The original filtering capacitors were introducing a slight 60hz hum into the audio, and I know a fresh set of electrolytics for the power supply would solve this issue. I have always used these Panasonic high temperature caps for replacements in other devices... always with positive results.

Before:



After:



The results? It sounded better... for sure! The 60hz hum was definitely gone. I always use the Panasonic 105 degree C. electrolytics in all my projects, the extra price is worth it. The overall sound with the new caps in the signal path? Better... definitely. The only problem was my ears were still annoyed at the louder right channel. Time to start checking resistor values. :(