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Hi all

About a year ago you helped me fix a Tek 2236 scope which is doing well ever since, for which I'm thankful.

I'm planning to tackle the refurbishment and / or repair of the 2445B/2465B scopes that I have before I move on to the older ones.

The 2445B boots up fine, but shows no trace. It smells of capacitors after a minute or two, so I don't use it any further. The 2465B works fine, but I have the feeling it has some issues focusing over the whole CRT. Either the middle looks sharp or the edges.

I started taking the 2445B apart and took out the PSU boards. The capacitors aren't good anymore (they are visibly leaking) and there are those dreaded RIFA caps on it too. I understand that both these scopes have the same or similar PSU and therefore I'll probably just replace all of the electrolytics on both boards, except the two large ones.

Are there any specific guides or recent capacitor lists available? I see that there are many threads and discussion about this. If nothing speaks against it, I would just replace the PSU electrolytics, the RIFA caps and the surface mount capacitors on the side board like for like for both scopes.

I also see that there are those Dallas NVRAM chips on board, I know them from old computers. While for an old mainboard they just hold meaningless CMOS setup data, I understand correctly that for this series of scopes they contain the calibration data?
Any suggestions on backing up these values? On some old mainboards I dremeled the Dallas chip battery contacts and added a regular lithium to it, but I would like to have a copy of the data before I attempt it here.
I have some old stock of these chips too, but I would have to check the remaining charge as well...

Thanks for any pointers.

Luca,

I did post a photo of the condenser and resistor list I did for my 2465/B. That is still there with Mouser numbers.

I had the Dallas chip in mine replaced with a FRAM by another exmemeber here.

Mark

See EEVBLOG >>2465 Teardown( 75 pages)

Check Condor Audio in Isreal and Qservice in Greec for repair/refurb tis and pars

Get full service manual for your model and serial, W140, Bama Archive, Vintage TEK museum

Follow procedures for check and repair flow charts.

Full printed many very handy avail from Artec manuls

Bon Chance

Jon

Hi Luca,

The calibration data for the 2445B/2465B and others in this family is indeed stored in the NVRAM. If you have a GPIB interface, there is a short procedure to retrieve (and restore if needed) the calibration data here:



Without the GPIB interface, the next best backup procedure is to take a video while scrolling through the stored NVRAM values using the EXER 02 diagnostic routine (described in the service manual). If you need to restore the values, you will need to program the NVRAM out of circuit. The addresses of the calibration data are described in the above link.

I'm not a fan of doing a drop-in FRAM replacement, because electrically it is not compatible with the Dallas power-up and power-down requirements for which the circuit was designed. I won't re-hash all the reasons here again, but you can search for why in this forum.

-mark

Have a look at the DS1230Y/AB nonvolatile RAm it uses EEPROM or FLASH memory and NO BATTERIES REQUIRED!

On 3 Feb 2024, at 19:01, DaveH52 <ac2gl.dave@...> wrote:

Have a look at the DS1230Y/AB nonvolatile RAm it uses EEPROM or FLASH memory and NO BATTERIES REQUIRED!

The data sheet at mentions “lithium energy source” which is presumably the usual battery.

Hi all

Thanks for all your inputs. I found some Excel sheets about the capacitors and will go through the boards first. Maybe I'll also do the big main board.. I don't trust any late 80s until early 00s capacitors anymore I've seen too many failed ones.

When I'm done with this or hit a snag I'll come back to this thread. Regarding the Dallas, good idea recording the calibration data. I got a video with the data for the 2465B. I hope I can do the same with the other scope after I get it running again and nothing is lost yet.

The DS1230Y/AB still has batteries, that would have been to easy...

I found this document with several solutions for replacing the Dallas chips
(after going through that PDF I'll try to find the reasoning against and then make a decision)

Hi Luca,
I think 2465B and 2467B share the same supply schematics. Based on my experience with 2467B:
- Component diagram may have C1132 and C1115 swapped (wrong). While desoldering take a note of the original value to make sure.
- NTC resistors RT1010 and RT1018 drifted quite a bit on my unit and most importantly R1010 was open circuit with a burn mark, check R1019 too. I replaced them with flameproof resistors.

Ozan

Caution in desolder of NVRAM, easy to damage PCB

We place a machined pin low profile 28 pin socket for easy replacement or backup with EEPROM reader/ writer

Jon

In my experience all pins can be sucked clean from tin except pin14 (Gnd).
With the other pins I did the following:
Remove as much solder as possible, (braid, tin-sucker, etc.) then use a small pair of pliers to just wiggle the pin in the hole to loosen it, before pulling the Dallas.
Do this for all pins except 14.
To remove the Dallas you need to heat pin14 while pulling carefully.
I never got pin14 clear from solder, but heating while pulling worked well.

Just my 2cts,

Leo

I looked at this issue some time back. As far as I can tell CPU (6802) can't do two data reads without CS toggling because it needs to fetch an instruction in between.

FM28V020 seems to be a 3.6V part, CPU board is a 5V design. It won't be happy seeing 5V long term.

Alternative suggested is FM18W08, which is a 5V part. However, it still has a potential issue. Dallas chip includes a low voltage lock out but FM18W08 doesn't have such protection and needs user to keep CE and WE in defined states all the time. Following text is from FM18W08 datasheet "It is the user’s responsibility to ensure that chip enable is HIGH to prevent accesses below VDD min. (2.7 V)." Unfortunately, supervisor chip (TL7705) output is undefined until 3.6V, there is no deliberate mechanism to protect the memory.

Although it works for many, it is not robust by design. FYI, I also installed an FM18W08 to try it out and it didn't lose its data yet. Most likely I will add a lower minimum supply voltage supervisor chip to eliminate this risk.

There is also a logic level incompatibility, FM18W08 guaranteed Vih is 0.7*vdd=3.5V but CE comes from a PAL chip at TTL levels (Voh can be lower than 3.5V). A pull up may fix it but at guaranteed specs logic levels are not compatible.

Ozan

=====

Yes the FM28V020 is a 3.6V part. My "memory" failed me there...cannot remember what exactly I did to accommodate that part in my 'scope. I've deleted my message so as to not mislead anyone. Once I take a look at what I did I will post the results here. I checked the 2465A I am currently using and that has a FM1608 DIP package from ePray.

Just use Ramtron FM1608 as pin-compatible replacement for DS.... it works.

Hi all

I found some time to repair the 2445B. There was some damage on A5 board from the SMD capacitors. I replaced most electrolytics on PSU boards except the big blue Spragues and of course the RIFAs.

On first power-up after repairs it would display TEST 05 FAIL 44, but not anymore. It appears to trigger correctly. It only has 300hrs on its clock, the Dallas RAM is from 1992.

Next I will have a look at the 2465B. I think I'll replace the same capacitors in the PSU (A5 board doesn't have surface mounted components, fortunately). Then I'll check the above mentioned components mentioned by Ozan. This scope has many more hours on it, like 5000. I only get to keep one, it will be a tough decision.
It has a Keeper II LTC-7P 750mAh, date code 0489 instead of a Dallas chip. I assume it can't be replaced by a Ramtron part? I'm thinking of ordering here:

leaky SMD lytics will emit corrosive fluid that destroys components and PCB inner traces and vias.

See the may notes on both groups io tekscopes and tekscopes2 as well as EEV blog for proceedure to restoredamaged A5 PCB with SMD lytcs.

Also see Condor Audio in Isreal and Qservice in Greece.

Jon

Just curious, what are people doing on the 10μF 100V caps? I replaced a couple with the recommended caps on the list on the inverter board while I was recapping the rest of the scope PS on my 2445, when I got to the regulator board I decided to check the 10/100 caps against the new, much smaller ones and found the old caps to still be good, in tolerance and esr/loss factor was much better than the recommended replacement caps so I put the old 672D 10/100 caps back in. The 100/25s I did replace because their values were all across the board, and the new ones I had were all very close to spec and better.

Jason,

I put in higher value condensers, 15-22mfd UHE types. This gives stiffer filtering and I know the new ones are better than original. At the age the originals are, I felt better with all new. I have 2465/B which uses the same supply.

Mark

Hi all

I found this blog post:



Is this an acceptable way to parallel the batteries for the discrete SRAM boards? I have some of those 1/2AA batteries from Macintosh repairs.

It looks like those blue caps can leak so I'll change them all as per your recommended series (I thought of keeping the good ones, but not anymore).

Furthermore, what's up with that massive heatsink on U800, is this mod really necessary? I have some self-adhesive heatsinks (for RPis etc.), would those be sufficient as well?

Thanks

STOP!

Do not fool with U800 horizontal sweep custom Tek hybrid

It doesn't need a heatsink and the screws are at -80V.

The mechanical is very critical, touching the screws can result in a dead scope.

See the many thread's on U800 Tektronix 2465B here, and EEVBlog

Just leave it alone.

Jon

Eek! I put a T-wing on mine! Do I need to carefully try to rip it off or am I okay as long as it doesn't touch the screws?