EBME Forums Forums Maintenance Technical Assistance Ohmeda 3800 SpO2 Monitor

I'm trying to restore a Ohmeda 3800 SpO2 monitor for preservation reasons.

I have manged to fix almost every fault it had including missing segments on the front display due to dry solder joints,and got the oximeter working again - again due to dry solder joints.

The only thing that isn't working is the alarm tone. If the desat/HR alarm is activated the visual alarm goes off (the display figures flash, and the yellow/red alarm lights come on), but no tone is made.

During POST the machine emits the correct test tones, and it also makes the pleth tone with each detected pulse beat during normal opperation. The alarm tone is also audible as a demonstration of the volume when you turn the volume up and down.

It's very annoying to say the least.

So from what I can tell, the alarm activation circuitry is working, as well as the speaker, amplifier, and tone generator, but there seems to be a broken link between the alarm circuitry and the tone generator?

Does anybody have any circuit diagrams or schematics of this machine? Or ever encountered this fault before?

I know I could just replace the controller board, but the only one I can find is in the US, and is going to cost a fortune to ship over - especially as it looks like a very simple fault to fix if I can track down the broken link!

Send me a PM malrdaw@gmail.com

Malcolm.

Welcome to the forum, James.

That's an interesting project; and it sounds like you're having fun.

Here is the manual. No circuit diagrams, unfortunately - but Test Points are shown (and listed).

Those were (are) nice little units. Orange displays rule!

Good Luck!

Thanks everybody

After getting hold of a replacement board for the monitor as described in the service book it still did exactly the same thing!

On further digging it seems that all audible alarms are deliberately silenced for the first 2 minuets from the time it is turned on! To overcome this you have to do an all mute then turn turn off the all mute function to enable all alarms.

How very strange!

But ... as mentioned in the User's Manual!