Incorrect, 24 pin EPROMs *are* pin compatible with the mask ROMs.
That is the whole point of using them.

Ah, sorry, thanks for the clarification. Are those 16k x 8 24 Pin EPROMs? All of the references I saw to the combined ROMs are for 16kB EPROMs. thanks.

On Tue, Apr 28, 2020 at 08:25 AM, Chuck Harris wrote:

If you ever find a Panasonic, or a Rubicon, or Nichicons or a
Rong-forU, or who-flong-dong for the larger caps, it wasn't done
by tektronix.

-Chuck Harris

Chuck,

This made me laugh! This is why I always enjoy your posts.

Thanks!
--
Michael Lynch
Dardanelle, Arkansas

Good Morning to All:

I was hoping to get some input from members regarding the issue with my SG503. This is S/N B030719, so early model. When I first received this unit, I cleaned the main switch contacts and checked for missing or unseated components. I found some IC's that were not fully seated. These were all removed and re-seated. All socketed transistors were removed, tested on a 576 Curve tracer and reinstalled. After powering up, the unit showed no signs of life when plugged in. I found the main fuse was not making contact with the fuse holder on one end. After adjusting that fuse holder for a snug fit, the unit powered up, but the display flashed, indicating an out of level condition. This was without any sort of output connection or termination. I searched the archives for similar posts and came up with some that seemed potentially relevant, but these lead to dead ends.

I have the manual and have read the Circuit Description and studied schematics. I have a working SG503, so I am generally familiar with the operation of the unit. I do not want to start poking around inside that unit for fear that I might cause some kind of harm to it as well. I can verify that my testing setup does deliver the expected results on the "good" unit. I have the correct cable as specified on the face of the SG503.

Using a 50ohm TEK terminator, I began to make some measurements of the voltages on the boards. -22V Power supply was set to -22.01. 4.5 supply checked at 4.62 and 5.2 V supply checked at 5.33, so nothing seems out of order with the supplies. I found these remaining functional problems, measurements and observations (in no particular order):

1: Display flashing in all output frequency positions. Displayed frequency agrees with knob position and scope confirms that correct frequency is available at output.
2: Amplitude control variable control R260 has no effect on amplitude of signal. Signal is over 5V in every frequency range.
3: Disconnecting variable pot R260 has no effect. Pot checks good @ 2K with smooth and even resistance throughout the adjustment range.
4: U280 pins 2 and 3 voltages are as follows -1.06V and -.668V. Pin 6 at -3.7V. Replaced U280 with known good component, just because I could do so, no change.
5: R265 (.5V Amplitude Set) DOES affect Pin 3 voltage when moved, this was set at about mid range and was returned to the original position after observing its effect on U280 Pin 3
6: R255 (5V Amplitude Set) DOES NOT affect Pin 2 voltage when moved, again, it was set about mid-range and was returned to original position after observations.
7: With my TDS460A connected using 50 Ohm termination, I found that the output in almost every range was a truncated or clipped sine wave of about 7.0V p/p (varies slightly with frequency).
8: In the 4Mhz - 8Mhz range, the sine wave appeared normal (not truncated) while the amplitude was still a bit high at 5.3-5.4V p/p on the scope. R260 still has no effect. Truncation or distortion of the signal seemed to begin above and below this frequency range. The sine wave appears to be truncated or distorted much more at the top of the wave than at the bottom of the wave. In the higher frequency ranges, the bottom half of the wave appears almost normal.
9: Frequencies in each range were relatively accurate and the variable frequency control has full effect on the frequency, as expected. Each range output agrees with the knob position and frequency can be varied within each range as expected. Compared to the known good unit, both units frequency outputs generally agree when tested back to back.
10: In the 250Mhz range, maximum frequency displayed is about 229.0 Mhz or less, depends on frequency range adjuster position. I blamed this on the excessive clipping that was occurring.
11: The attenuation selector switch works in all 3 positions. Signal attenuates as expected.

This leads me too think that the leveling hybrid U225 is somehow "Bad". I do not fully understand how this circuit works, so forgive my ignorance. How can this device be tested? Or does someone have other ideas about this problem?? Any Advice is appreciated!

Sincerely,
--
Michael Lynch
Dardanelle, Arkansas

On Tue, Apr 28, 2020 at 7:12 AM Paul <devpool0@gmail.com> wrote:

This is not quite correct. If you use 24 pin EPROMs with the combined
images, you don't need the FPLA.

24 Pin EPROMs aren't pin compatible, so that'd be what I described as option 2, right?

Incorrect, 24 pin EPROMs *are* pin compatible with the mask ROMs.
That is the whole point of using them.

Are the 27128 & 2716 programmable in the TL866?

http://www.autoelectric.cn/MiniPro/MiniProSupportList.txt

Also, you can use the CY7C264 EPROM, which programs at 12.5V.
(Unfortunately it's still not supported by the TL866.)

The CY7C264 would be drop-in replacements for the original ROMs?

Yes, they are also 24 pin.

I do actually have a fully functioning 475A, with printed manual here.

On Sat, Apr 25, 2020 at 02:46 PM, Bill wrote:

Good thread.
https://groups.io/g/TekScopes/topic/tektronix_465_no_trace_no/7656979?20,1,20,0

Good info here to:
https://lazyelectrons.wordpress.com/2018/02/18/tektronix-475a-dm44-repair/

Bill

Thanks Bill,

those links were interesting but one was unresolved, and the other was for a 475A and had a dot once he had the LV rails sorted.
Mine has the LV sorted but still no dot. Not even with beam find. Only when the neons buzz.

So after appearing to stop, there is still intermittent buzzing from the neons, although only when the 5000µF, +5v filter cap is installed, which signals to me that something is (still) wrong on the +5v rail.
Strangest thing it that this issue only appears with the scope upside down (A9 interface board faces up).

I want to test the voltages but have arrived at the point where you cannot see the wood for the trees, so don't know whereabouts I should be measuring.

Doesn't help only having a .pdf of manuals which aren't very clear and having no access to a printer.

Think I just need a break. I have spent more days on this than I can count.

I recently recapped my 2445 and you'd definitely see the differences between mine and a factory. The new caps are much smaller and, typically, the lead spacing is smaller so they don't sit tight to the boards. I didn't really like that but it works so I left it along. :(

Thanks,
Barry - N4BUQ

And,

If you truly have two different power supplies with these
capacitors in different spots on the supply's circuit board,
you must get them both right, as an explosion is in your future.

A lot of these boards have had their capacitors replaced, and
anyone with a little talent can do the job so it is all but
indistinguishable from tektronix's original soldering.

But, many, many of these jobs were done in a dumb way, where
the worker removed all the capacitors and then used the manual
as the guide to put them back.

In all my years of working on tektronix equipment, I have found
that their manuals are terribly deficient in the circuit board
layout diagrams. It is rare to find one that is completely right.

I wonder how many of these 2465 power supplies have been recapped
multiple times? I would bet a whole lot.

The original supplies had Orange, or Green, and much later blue
capacitors for the 100uf, 180uf, and 250uf values. These were
generally without an obvious manufacturer's mark or logo.

The original smaller caps were all black Nichicon.

If you ever find a Panasonic, or a Rubicon, or Nichicons or a
Rong-forU, or who-flong-dong for the larger caps, it wasn't done
by tektronix.

-Chuck Harris

Siggi wrote:

Hi Dan -

I have firmware version 1.03, which is made up of the following ROMs:

U100 160-0408-01
U110 160-0409-01
U120 160-0445-02 (Signetics 3-state FPLA)
U200 160-0410-01
U210 160-0411-01
U400 160-0466-02 (8x2k EEPROM)
U410 160-0467-02 (8x2k EEPROM)

OK, so v1.03 has -01 suffix mask ROMs and -02 suffix FLPA / EPROMs.
I have -00 suffix everything. Do we know what version that would be? Is the version shown on boot, or are their any other markings that would indicate the version?

Interesting stuff re timing - I'm going to dig into that after work.

Cheers
Paul

Hello Holger!

Ah yes - that is the picture that I Klaus posted. Very excited to hear of your progress. Is Firmware 2.0 what was on the later, combined ROM/RAM board?
cheers,

Hi David -

This is not quite correct. If you use 24 pin EPROMs with the combined
images, you don't need the FPLA.

24 Pin EPROMs aren't pin compatible, so that'd be what I described as option 2, right?
Are the 27128 & 2716 programmable in the TL866?

Also, you can use the CY7C264 EPROM, which programs at 12.5V.
(Unfortunately it's still not supported by the TL866.)

The CY7C264 would be drop-in replacements for the original ROMs?
I've got a BP Microsystems EP-1... somewhere, but don't know it's working state or capabilities.
cheers

If you search through the archives, you'll find plenty of posts discussing
this. The manual has these reversed as I understand, see e.g.
http://w140.com/tekwiki/wiki/2465_Series_PSU_Repairs.

On Tue, Apr 28, 2020 at 2:22 AM Don N3DEB via groups.io <dbawatsonville=
yahoo.com@groups.io> wrote:

I am recapping a working 2465 to ward off any future failure, my second
recap of this model. This one seems to have the 2465A PS boards as the
layout is a bit different.
It also has a power wire next to A3C1115 that routes to the case fan
positive. The fan is a common square computer type. It has a factory shroud
holding the fan in place and is very low tech.

But most unusual is that I found two caps swapped but does not look like a
botched repair. The soldering looks factory, untouched just like every
other part. In fact I spot no repairs anywhere in this scope.

According to the service manual:

A3C1132, 10uF, 160V
A3C1115, 250uF, 20V

These are swapped in this scope. Replace per manual, right?

Thank you

If you check back in the archives for this group, you will
find that in some versions of the manuals the identification
numbers for two caps on the power supply are switched. If you
follow the book, you will make an explosion of capacitor guts.

-Chuck Harris

Don N3DEB via groups.io wrote:

The manual is wrong on these two caps. Also, it's not a 2465A power supply it's a later version of the 2465 power supply.i
Later versions of the 2465 have the muffin with the requisite changes to the LVPS for controlling the fan.

I would venture a guess that your scope is in the high B02xxxx s/n, most likely in the B05xxxx range.

--Victor

Hi Paul!
and all the others of course ;-)

I'm "Klaus's friend" ;-)

I've created the prototype for a new 7854 ROM board plus an overlay card - here are two more pics:

http://www.methodyn.de/p/proto11.jpg
http://www.methodyn.de/p/proto12.jpg

The ROM board will fit in all 7854 scopes (1) and with the help of a switch you can boot up into 4 different firmware images.
I've successfull tested the 1.03 firmware and the diagnostics rom (2). Testing of Firmware 2.0 and maybe older versions will follow in the next days.
At the moment the design is still in the prototype stage - and the "specs" may change for the final product.

Greetings Holger

(1) Yes, I'm aware of the design change in the 7854 starting at #100000
(2) http://w140.com/tekwiki/wiki/067-0961-00

Hi Christian,

As for PCB edge connector with "gold fingers", I've tried it with my TM500/TM5000 extender project.
JLCPCB offers them along with ENIG surface finishes and chamfer on edge.
Results have been quite good. And it's not that expensive, around an extra $20 for that option.
I got my 5 prototypes PCB (70mm x 107mm) for around $30 shipping included.
I would say it's economically feasable to design a new PCB.

Best regards,

Hello,

I browsed through all the files I had about the 7854 ROMs as well as all the A31 ROM board
surgery I did in the past. Having all the resources needed to reproduce the latest Tek
combined RAM/ROM/Battery A28 PCB (670-9520-02? difficult to read), I noticed that I
couldn't find anywhere the latest ROM images used on this board i.e. 160-3724-00 and
160-3725-00. They would find a good home on tekwiki anyway.

Does anybody have access to these ROMs and can post their content for posterity?

Something compatible but perhaps not as much bug free could be produced out of the
old images and board schematic but it would be lost time if the right info is readily available.

Designing a PCB is possible for me but producing it with hard gold fingers is quite expensive.
There are/were connectors essentially reproducing the gold fingers and ending in surface
soldered legs on the PCB (launchers?). If somebody finds a source with such compatible parts,
it would for sure be possible to design a PCB compatible either with hard gold plating
or connector adapter just by changing the PCB border path and production method.

Using chemical gold (ENIG) is perhaps acceptable for a single insertion board?
This is a very thin gold layer that is just meant for air protection and dissolves readily
in solder. In any case, it is not hard enough for repeated mating, but perhaps for a
single and careful insertion it would be a cheap acceptable alternative?

Christian.

Sorry, you're right.
The silkscreen is not what I was meaning to say, it's the location of the parts shown on the component layout in the manual that has the location of c1115 and c1132 mixed.

I have manual rev Jan 1989, in figure 10-13 is the mixup on the A3 board visible.

I usually replace c1113-c1116 by 330uF 50V, and c1120, c1130 and c1132 by 10uF 250V

Sorry for me being unclear.

Leo

The silkscreen does not identify the cap, only the polarity.
Apparently it has been working fine all these years with a factory assembly error!

My other 2456 had them as per the manual. Just wanted to make sure I did not miss a manual revision. The serial is B030879.

Manual is right, silkscreen is wrong.
Replace one cap at the time and your ok.