SR-52A rebuild project (SR-52A 942058 LTA4176)

[albertofenini]

Hi everyone

while restoring the SR.52 we have, a couple of spare units came out from our drawers
these are pretty beaten up, but we should have almost all the parts

we started yesterday with one of the two, and thanks to the contribution of
Klaus Overhage we also have pictures of how to re-connect the card reader

these models are different, probably earlier versions, from the two we restored last weekend

card reader is attached in a different position and components layout is also different

one doubt we have is the following : in our model close to the upper battery contacts there is a transistor,
but there are also markings for another one called Q4, this is missing on both our spare units

we don't recall if we removed or not, but looks like those marking are untampered ...

anyone can tell us what kind of transistor is ?

pictures of the restoration can be seen here : SR-52 942058 LTA4176

[Maximilian Hohmann]

Hello!

(03-05-2021 09:12 AM)albertofenini Wrote:  Q4 ... anyone can tell us what kind of transistor is ?

Did you look in the SR-52 troubleshooting guide? http://www.decodesystems.com/TI_SR-52_Tr...ooting.pdf

I have looked through it but it is difficult to tell what Q4 is - it is shown in one of the last pages.

Regards
Max

[albertofenini]

Thank you Max,

I have that document but it's not clear what kind of transistor is,
maybe this could be a PCB revision that doesn't need it ...
I do remember stripping some of the components but not that particular transistor
Will work on it probably this weekend, starting by re-soldering the missing ICs and will see !

thanks again take care !!!

(03-05-2021 01:07 PM)Maximilian Hohmann Wrote:  Hello!

(03-05-2021 09:12 AM)albertofenini Wrote:  Q4 ... anyone can tell us what kind of transistor is ?

Did you look in the SR-52 troubleshooting guide? http://www.decodesystems.com/TI_SR-52_Tr...ooting.pdf

I have looked through it but it is difficult to tell what Q4 is - it is shown in one of the last pages.

Regards
Max

[jebem]

Q4 is used with Q3 as a Darlington pair to drive the motor on the original SR-52 model PCB.
Q1 and Q2 are used as the Darlington pair to drive the motor on the SR-52A revisions.

Q4 do not have special requirements in this position, any npn high current type is adequate, see the Q2 specs on the SR-52A revision, it should be similar.
I would say a npn with IC of 1 ampere maximum and VCE of 20 volt would do the job.

[albertofenini]

Thank you very much
However, the SR-52 troubleshooting guide never mention a Q4,
it mentions a Q1, a Q2 and a Q3
I need to go back to the PCBs and take a good picture
On the other side, I don't remember removing a Q4 and the holes on the PCB look really untampered
Do you mean that if Q1 and Q2 are present, then Q3 and Q4 are not necessary ?
Please bear in mind that on both spare units Q3 is indeed present
Thanks again for help
If you have any picture that would be of help
In the pictures provided by another firm member, in order to reconnect the card reader, I can spot a Q4 ...

(03-05-2021 03:33 PM)jebem Wrote:  Q4 is used with Q3 as a Darlington pair to drive the motor on the original SR-52 model PCB.
Q1 and Q2 are used as the Darlington pair to drive the motor on the SR-52A revisions.

Q4 do not have special requirements in this position, any npn high current type is adequate, see the Q2 specs on the SR-52A revision, it should be similar.
I would say a npn with IC of 1 ampere maximum and VCE of 20 volt would do the job.

[albertofenini]

A closer look at the Troubleshooting guide reveals :

   

so it may be that the board is missing transistor is because of that
The document refers to this as a Q5 while on the PCB the marker says Q4 ...

Anyone knows where can I find the version of the board ?

[jebem]

Hi, Alberto,

The information I gave you is taken from the SR52 service guide that I bought on eBay long time ago and later I made it a available to all community thanks to Katie.
Please see the schematic diagrams for both versions of the 52.

I dare to link here to my own findings at the time, hope that this action will not be censured here as it was in the past with another project of mine.
Please browse the pages until you see the link to Katie's website where the service manual was uploaded.

Gene's thread hijacked by me on the SR-52

Wish you good luck with your project.
I didn't quite restored my SR-52 as other tasks were taking my time until I forgot about it.

[albertofenini]

Hi Jose

thank you very much for your message and your support

I had read all of the thread when I started to restore the two SR-52 that where complete and running
Those two units S/N 953114 LTA4176 and S/N 014131 4775DTA are of the same version of the one you have
pictured in your post, card reader is attached to the main board on the upper left corner (component side) of the PCB
What kind of version is this ? SR-52 or SR-52A (just to know)

The service guide you mention is the "SR-52 and SR-52A troubleshooting guide" ?
If that is the one, I have it and I have read it throughly, still I couldn't find a reference to Q4

These other two units, which I had dismantled almost fifteen years ago, and of which the working status is unknown ,
are however of a different type, they have four green capacitors in the upper left corner and the card reader
is connected closer to the battery terminals

   

These units S/N 942058 LTA4176 and S/N 086513 LTA5176 with the green capacitors which version of the SR-52 are ?

Also I looked in the Etienne section of the post but I'm afraid the links are
expired, images won't load and the link referenced is not working

What am I missing ?

Thanks for help !

(03-05-2021 05:16 PM)jebem Wrote:  Hi, Alberto,

The information I gave you is taken from the SR52 service guide that I bought on eBay long time ago and later I made it a available to all community thanks to Katie.
Please see the schematic diagrams for both versions of the 52.

I dare to link here to my own findings at the time, hope that this action will not be censured here as it was in the past with another project of mine.
Please browse the pages until you see the link to Katie's website where the service manual was uploaded.

Gene's thread hijacked by me on the SR-52

Wish you good luck with your project.
I didn't quite restored my SR-52 as other tasks were taking my time until I forgot about it.

[jebem]

Hi Alberto,

I can't really tell what version I have because I am temporally away from home, taking care of my old sick parents.

But I wouldn't worry to much about the version, as there are several releases of the 52 PCB (A to L, if my memory is not failing), and at least one version of the 52A, and of course several modifications were introduced, from circuit design, PCB layout, components selection (brand, floors, etc).

In the manual, look for the schematics diagrams, pages 37 and 39, you should be able to find on the right side of each page a symbol for the Motor, and one terminal is connected either to Q2 or to Q4, depending on the schematic version.
With a multimeter we can check where the motor is connected, it will be to a collector either to Q2 or to Q4.

[albertofenini]

Hi everyone

I have added few more pictures to the initial link
I have also mounted the TMC0501
First try to power up failed ?
Has the keyboard to be connected ???

Based on the components mounted this unit should be a SR-52A

Tomorrow we will try to measure few voltages and try to troubleshoot something
Any suggestion is welcome !!!

EDIT actually is not completely dead
For a while a 20000 was blinking in the left part of the display
When Turning off and on a faint -. In the most left part also lit
Then only a very faint . In the left part of the display stays on
I have added video of the power on to the pictures album
Please keep in mind the keyboard is disconnected

Pictures and videos here : SR-52 Rebuild project

[albertofenini]

Hi Jose, best of luck with your parents !!

(03-05-2021 08:26 PM)jebem Wrote:  Hi Alberto,

I can't really tell what version I have because I am temporally away from home, taking care of my old sick parents.

But I wouldn't worry to much about the version, as there are several releases of the 52 PCB (A to L, if my memory is not failing), and at least one version of the 52A, and of course several modifications were introduced, from circuit design, PCB layout, components selection (brand, floors, etc).

In the manual, look for the schematics diagrams, pages 37 and 39, you should be able to find on the right side of each page a symbol for the Motor, and one terminal is connected either to Q2 or to Q4, depending on the schematic version.
With a multimeter we can check where the motor is connected, it will be to a collector either to Q2 or to Q4.

[albertofenini]

Hi guys
We have attached a keyboard
Didn’t change much but something happens
At first we have got a blinking number on the left
Then pushing the LRN key make a 0 to show up

We started to measure and while VGG is about - 11.95 VDD is about - 6.18
and what I think is Vss (+ terminal of C10) is about VBatt

WhAt do you think ?

Check pictures and video here : SR-52 Rebuild project

[albertofenini]

Differences between SR-52 and SR-52A, testing Vdd, Vgg, Vss, Vbatt

Hello Everyone, few updates for today :

we are almost certain that this unit is a SR-52A, while the two we restored are most probably SR-52 REV. D thru L

we tested all of the voltages from this unit and we compared the values with those from a working SR-52
the differences are
1. a SR-52 uses a TMC0524 where a SR-52A uses a TMC0534
2. a SR-52 uses a CD4011 AND a SN96239 where a SR-52A uses only a CD4011
but all the voltages measured at every IC where identical between the two units
we have also noted that Vgg in the documentation is expected to be -15 V and actually is about -12 volts for both units
while Vdd in the documentation is expected to be about -10 V while in both units is about -6.24
Vss is about Vbatt for both units so we believe is ok

we attached a scope and we have found the SR-52A (the one that doesn't work)has a good Clock 1 and Clock 2 signal
exactly as the working SR52 in all the points where it is supposed to be

current consumption is also identical between the two and is about 170 mA when showing a 0 (or for the SR-52A what is should be a 0)

We have found however different waves around the TMC0501 in the non working unit
However, since this is the area where the PCB was badly ruined, before removing and trying to replace that chip we would
appreciate some suggestions on the possible cause of non working.

Any idea ?
Thanks for help !!!
Take care !!!

[albertofenini]

Replacement of the Display Driver

Another step forward ...
After replacing the TMC0534 and the TMC599 with no effects
we have found out that one of the SN27882 had a corroded pin which broke ...
Replaced that the display turns on but ...
None of the numerical keys work, it goes in LRN mode and some of the keys like the first column is ok, sto and rcl seems ok with few others ...
Now the question is how can we understand if it’s a keyboard problem or a TMC534 or a TMC501 issue ??
Thanks for help !!!!

[albertofenini]

How to find a keyboard failure

If we short with a thin wire rows and columns at the pcb side the calculator works
and numbers are displayed and operations can be done

However, when the few working keys are pressed on the keyboard
the corresponding row and columns are not shortened together as we were expecting

As an example : the LRN key works and is obtained with column 4 and row 8
If we put an ohmmeter between this two points when we press the LRN key [/align]they don’t get shortened

I think we are missing how the keyboard works and this make difficult the repair

Any idea ?
Thanks for help !!![align=justify]

[albertofenini]

Rebuild of the keyboard

Hi everyone !!
Another small step forward

We have completely dismantled the other spare unit keyboard and
cleaned every single dome
First tests show that all the keys are now functional
We are using the wires that usually come with a breadboard
in order to replace the original cable connector

Next steps are now to glue back the facelift using double sided tape
And reconnecting the card reader

The card reader is mechanically working
We have rebuilt the gummy wheel and a card
is transported with constant speed across the card reader

Electronically tests still to be done

AAA batteries springs are on the way and will be used to replace the broken battery contacts

Update pictures link here : SR-52 rebuild project

[albertofenini]

The repair of the battery contacts, rebuild of the card reader, faceplate

Hi everyone

This is the current situation

Using the AAA springs we have rebuilt the battery connectors
We have also glued back with double adhesive the front plate
It will take now 24 hours to strengthen but it looks ok

We have also reconnected the card reader
However when a card is inserted nothing happens
Basically the engine doesn’t start

We have cleaned the card switch which was always open but still the engine doesn’t start
We had previously checked the engine and if powered externally it works fine

Tomorrow will check the card reader circuit starting from the U7 and will see

Suggestions and ideas are very much welcome
Take care !!!

Update album is here : SR-52 rebuild project

[albertofenini]

Card reader kind of working, keyboard connected, faceplate almost done

Hi everyone

today we replaced the original keyboard with the restored one
Since we didn't want to fiddle too much with the pcb we decided to use a SIL socket
This will be the first SR-52 with a removable keyboard
At this stage there are two connectors, one will be removed before closing the unit
It will also probably be necessary to modify the lower half of the case in order to
accomodate the thickness of the SIL

We have also cleaned the card switch and re-soldered the cables
Cleaned the head and lubricated the card reader motor

The good news is that card reader now start and transport the card quite well
The bad news is that it doesn't read ...
Will investigate what the problem could be between these possible causes :
- head dirty or not working
- not enough pressure between the card and the head
- amplifier not working

We have also given a look at the faceplate, it's not bad but it tends to detach
from the upper side of the frame so we have put it under pressure again ...

take care !!!

Few more pictures at the usual link : SR-52 rebuild project

[albertofenini]

Card reader works, reads and writes

Hello Everyone, the card reader is now working

First we disconnected the card reader and checked the resistance for every channel
Yellow with Black : 681 Ohm
Green with Black : 675 Ohm
Orange with Black : 700 Ohm
White with Black : 718 Ohm

we do not have (yet) an Impedance Meter so we couldn't check those values as well
but never mind, the head looked ok, we polished the face of the magnetic head with
a Dremel and a cotton tool, is less aggressive than using the cleaning card which is
abrasive and has the same effect as for removing the dirty patina

one thing we learned todays is that rather then putting oil in order to lubricate
the card reader motor (we were using WD-40) is way better to use a contact
cleaner (we uses Deoxit D5)

we think this is because probably the reason for a noisy and slow motor is that the electric brushes
that can be seen from the bottom removing the small black cover are oxidized and the contact cleaner
makes miracles, now the motor is fast and way more silent than before

Then we removed the TMC0595 (our is a version D, it was printed on the bottom)
We cleaned underneath and we also removed and checked all the capacitors C12,C2, C3, C4, C5
checked the nominal value and in the end we used those from the other spare unit as they were .004 microF
which was closer than the original ones to the nominal value of .005 microF

Meanwhile we discovered and fixed (again) the keyboard that had a loose joint for the fifth column which made
Impossible to do any calculation being that the column with the operation keys and the equal key

Re mounted everything and ... voila

It reads all of the BA Libray and we have also been successfully copying the card BA-1
Diagnostic cards also produce the expected result

Next step : check the faceplate and close everything ....

We may as well try the same operation on the other spare unit, but first we need to find a good
SN27882 because we took one from that unit to repair this ...
It's available new on line or it can be found on all of the SR-50 models

Picture and video updated here : SR-52A rebuild project (SR-52A 942058 LTA4176)

[Gene]

Real real shame the TI model card readers are 1) so comparably difficult to repair and 2) a lot fewer people care and have skill / experience repairing them.*

Put together, these two things mean most TI models with card readers that die stay dead. That's one reason I recommend the TI-58C. Most of the benefit without the dead card reader.

It's also a reason my four SR-52 units will never read a card again... :-)

Gene

* I totally understand #2 here, just pointing out the reality.