LCD display on exercize bike troubleshooting.

If something is dragging the voltage at the batteries down 5 volts that's going to consume a huge amount of current seeing it's almost a short circuit. I doubt any of the internals would be able to sustain such a current draw without making a little smoke. I'd check for a bad connection within the battery cage itself. Maybe where the contacts are riveted to a supporting structure. This makes more sense to me.

Yes, except for the problem didn't occur until I pressed the start button on the panel. a soft button, btw. That kind of leaves out a constant short from the battery box.

Check for a cap that is leaking in the display circuit. It should be easy to determine, but might require one lead be lifted in order to do so.

Didn't say a short. I said a poor (bad) connection. Learn the difference.

Before you get all tangled up, try a set of NEW batteries. If you are testing with a digital meter you are putting essentially no load on the batteries. Where in the circuit did you access the voltage reading? If the batteries are truly good, just probe along the connections from the batteries to the display to find the high resistance culprit.

Charlie

Are you looking at the batteries themselves? Or, someplace else in the circuit? 4 cells won't drop to 1/4V each (on average) unless they are *shorted* (otherwise, several would have to be "completely flat" -- in which case, they wouldn't read as 6V open circuited).

Are the battery terminals corroded?

I did test at the battery contacts in circuit. They are new batteries. I could try some other new batteries but I suspect these batteries should work. That said I did plug in an ac adapter, 6v 2A, and it acts the same with or without the batteries installed.

I checked the voltage at the ends of the set of 4 batteries as installed by probing the ends of the batteries in circuit. There is no corrosion. They are new alkaline batteries.

I haven't taken the whole thing apart to get a look at the PCB, the problem may be evident when I get home and try that.

I liked the leaking cap suggestion from earlier. It could be something like that.

Can you insert a DC ammeter in series with the b+ line to the board and report back as to the current draw?

I took the whole thing apart. I found a broken ceramic disk capacitor. Actually broken. Near the display area. I replaced it, it was a .1 mfd, same as it was.

That didn't help. Inspection didn't reveal anything else obvious.

While I had the LCD out I tried it on the board a little moved it around. It has those rubber conductive connections. I did get bright flashes on some parts of the display, the word "AGE" lit up brightly, so the display works

" snipped-for-privacy@my-deja.com" wrote in news: snipped-for-privacy@4ax.com:

a new set of cells? This low V is why your LCD is dim.

If the display "works",but it's light,the drivers are probably OK. It might be a bad Vcc regulator IC.

perhaps bad electrolytic caps? they can be a common failure. do you have an ESR tester,such as the ANATEK/Dick Smith model?

" snipped-for-privacy@my-deja.com" wrote in news: snipped-for-privacy@4ax.com:

ah,perhaps you need new rubber connector strips. where to get them,I don't know. Maybe MCM,maybe the manufacturer of the exerciser.

So, it's drawing (considerably) *more* than 2A (in order to drag the 6V supply down to 1V)? What exactly *is* it drawing?

I don't see an obvious regulator IC, or anything that looks to be power supply, really. This is a cheaply made chinese board, one ic under a glob of epoxy connected directly to the LCD. Lots of diodes and caps. No obvious stuff for making the LCD work, seems integrated in the one ASIC.

Only three electrolytic caps on the board. I tested them with an EDS-88A cap tester. They seem OK.

So I dunno.

Let's apply Sherlock Holmes' rule about eliminating the obvious.

If the display flashes or briefly displays "something", the problem might be the contacts.

Try carefully cleaning the contacts on the board. You might also try cleaning the conductive-rubber contacts on the LCD, but this requires using a lint-free swab, and "rolling" (rather than rubbing) the swab over the contact surfaces. Be vewy, vewy kehful.

Duh... I meant impossible.

It's likely that there will be a warm/hot component on the board, where the majority of the current is being dissipated. That may indicate the vicinity of the fault.

If you power the circuit on for 5-10 seconds (with good batteries or AC/DC adapter) then power the circuit off (disconnect the AC/DC adapter), you may be able to detect a heated component with your fingertips. A longer power cycle may be needed, but avoiding excess on-time may be beneficial.

I only mention this method for this low voltage, battery powered circuit, because there is essentially zero chance of any electrical shock hazard with the power turned off, after a brief power-on period.

Feeling around for warm components on any line powered equipment circuit boards could very likely be hazardous, even with the power off, and should not be done as a troubleshooting method.

There is a plastic sheet product that indicates thermal changes, but I don't remember what it's called. The sheet is placed on a circuit board, and warm areas change color.

If you know anyone with a thermal/Flir scanner-camera, it would likely show a heated component on the board.

I doubt that an infrared sensitive surveillance-type video camera would be sensitive enough to spot heated components with, but if you have access to one, it may be worth a try, with the test area lighting turned off.

-- Cheers, WB .............