BT Cheetah similar to LO3000 - Repairing.

[M1ECY]

Hi all,

So, I have looked a little deeper into the BT Cheetah, from what I can see it is almost a perfect copy of the LO3000 - pictures to follow.

I have cleaned a lot of the dust and dirt from the PCBs inside the machine, and have repaired a problem with the X2 capacitor fitted inside the power supply.

This far, the power supply is giving all the correct supply rails to the motherboard (tested by removing the line interface card to get to the test points on the motherboard).

I have substituted the battery supply from the battery back up with my bench PSU just to make sure that everything is getting power where it should.

However, this is a poorly machine THe screen displays lots of random characters, and the illuminated keys on the keyboard are all illuminated.

I think there might be a problem with the CPU at the moment - either the eprom containing the data for the TP is dead, or the processor has a problem.

Does anyone with experience of the LO3000 have any ideas where to turn?

Thanks
Sean

[DF3OE]

The Cheetah and the Lo3000 are absolutely identical. It's like Opel and Vauxhall models.
It was a joint development of SEL and Creed, both ITT companies back then.
Therefore you should be able to use all the available Lo3000 documentation for repair
attempts.

Good luck!

[M1ECY]

Hi Henning, Thanks.

The manuals as uploaded here have no schematics - perhaps these do not exist.

So far I think it has to be one of the three possibilities.

1, reference oscillator for CPU, or other parts of controller defective

2, corrupted Eprom containing program for machine

3, defective processor

In all cases, none of the keyboard keys work.

There is a green lamp illuminated on the CPU board, so I think the CPU is doing something.

This is one area where I have little or no experience - there are no tubes other than the CRT!

[M1ECY]

I am looking at the Lo3000 service manual, Section 6.6.

I think, as a combination of my very poor German, and some help from Google translate, there are instructions there regarding how to perform a cold start reset?

Perhaps this will be required on my machine due to the back up battery being defective after so many years without use?

Am I correct?

Thanks
Sean

[Patrick]

I am looking at the Lo3000 service manual, Section 6.6.

Hi Sean,
the LO3000 service manual will not give you detailed schematics, just function blocks. Chapter 6.6 attached below.

Regards
Patrick

[M1ECY]

Thanks Patrick, I have "read" (well, google translate has) that part of the manual, but I think my problem lies deeper.

The green lamp on the CPU board is now not functioning, so I think that perhaps the processor is not happy.

I include a picture of the processor card

I will pop a hopeful post in the parts wanted section to see if anyone has a set of PCB cards for the LO3000

[Patrick]

Hi Sean,
as long as your power supply is still good, you can be lucky. I have blown 2 of my LO3000's with some fireworks inside the casing. Almost all parts on the primary side of the power supply burnt down.

Does anyone with experience of the LO3000 have any ideas where to turn?

LO3000:
In case the battery is emtpy, you need to remove it and switch the teleprinter on (without having the battery installed). Once the unit started without the rubbish on the screen, you need to plug-in the battery (while the unit is still on).
This procedure is described in the manual (item 6 and 7 below). Complete initializing as per chapter 2.2.2:

Erstinbetriebnahme (Initialisierung des Geräts)
1. Netzstecker stecken (Batterie und Service-Stecker
dürfen nicht gesteckt und Service-Schalter muß
ggf. in Stellung »Normalbetrieb« sein!).
2. Service-Stecker stecken bzw. Service-Schalter auf
»Servicebetrieb« umschalten.
3. Editieren der Techniker-Wahlfunktionen und ab
speichern im CDP (s. 2.5.).
4. Service-Stecker ziehen bzw. Service-Schalter auf
»Normalbetrieb« umschalten.
5. Netzstecker ziehen.
6. Netzstecker stecken (wie bei 1.).
7. Batterie stecken.
8. Editieren der Bediener-Wahlfunktionen.


Regards
Patrick

[Patrick]

Sean,
in case I find some time next days I can double check with my LO3000 which LEDs turn on when starting the machine. My LO3000 has a DIY power supply which is not 100% in line with the original PSU, but the teleprinter works with it.

[M1ECY]

Hi Patrick,

Thanks for the news

The one thing that does work properly in my machine is the power supply!

So, it would seem for testing, there really is not a need for the battery to be present at all.

Certainly, the processor board in this machine is not working as it should.

I have tried to power the machine up both without the "battery" (in my case I have substituted a power supply because the cells are defective)and with this auxilliary power supply connected.

In all cases, the rubbish on the screen is all I can see.

Does this mean that you may have some spare parts available?

Sean

[Patrick]

Does this mean that you may have some spare parts available?

Hi Sean,
not really as I need to save the parts for the current working machines. I only have a LO2000 as spare / partly cannibalized already

I know there are other members in this group with similar power supply damages, not sure if they ever plan to repair the unit or sell the other components to salvage/ help other LO3000 users.

hopefully they have not scrapped the units

Regards
Patrick