Temperature alarm in POD

[sebastian]

Hi all,

after restoring my sinclair c5 (https://plus.google.com/photos/102914470871796640086/albums/5800744213002721249) I have not used it for three month, now I wanted to reactivate it and it shows a motor temperature alarm. The left side of the POD is flashing. I have found the exact alarm here:

http://c5alive.co.uk/forum/index.php/topic,723.msg5860.html#msg5860

After reading this I have replaced all electrolyt capacitors in the POD, but the error is still alive. Opening the control box all seems fine. Fuses are ok, and the C2 capacitor seems to work. Now I have checked the two thermal resistors by disconnecting it and checking the values. First: Do they work as normal resistors? Because the inner sensor have 16kOhm, the outer seems to have 0Ohm. Very strange. Do anyone know the "normal" values?

What I want to check next is to replace the thermal sensors with static resistors. Can this work for a test? But what values...

Next is to replace C2 in the control box, but this I want to do after all the other testing.

Anyone have better ideas to check where the alarm comes from?

Thanks a lot!
Sebastian

[sebastian]

Ok, I have now replaced the C2 on the Control Board, and I have tried to replace the temperature sensors with two 10kOhm resistors. Same alarm  Now I have no new ideas where the mistake could be. Next is to check all wires between CB and POD. But anyone more ideas?

Thanks, Sebastian

[radiomarty]

Hi check the op amp in the control box- Regards Marty

[gertk]

The outside 'sensor' is a simple thermal switch (like a thermostat) and should read 0 ohms when cold.

[sebastian]

Hi,

thank you, I will replace the IC now, and look what happens! Will inform you again, thanks ;-)

[sebastian]

No success...  I have now replaced all Elcos in POD and CB, and changed the LM358N to a new one (in a nice socket ;-)). But it shows the alarm when switching on.

Are there any possibility to override a part of the circuit to check which part is out of order?

Thanks, Sebastian

Edit: I have now tried to simulate the thermistor with an variable resistor, in the range from 900 to nearly 1100 Ohm (I found this as the "normal" values). In this range, the lights are flashing too, but the POD is beeping, too. Another reaction, same failure.

Any more ideas? How can I bridge this failure?

[radiomarty]

Hi I have known this fault when the thermal sensors are in the wrong position - make sure the orange wires are in the middle position - and the violet on the outer edges - there are only a few more faults  really which is the 3 transistors in the control box or sadly the ULA chip has suffered some form of static damage. As this should reset its self have you left it on for a couple of hours ?

[sebastian]

After month I have give it a new try, same failure. Then I have bridged the POD with a resistor (2,2k) between PIN 3 and 7. No POD but it runs again. It seems that the POD is giving the alarm. I have changed the capacitors to new models, but same failure. Any more ideas? Next step is to change all elements in the POD, any idea where to start?  THX!

[dansretropod]

Sorry to say it but its most likely the ula and there aint no replacement for that other than taking one from another pod.  I did make a ula replacement module using an arduino nano but have not got any left.