help!! no tach, no output from CD

[jpnovak]

I am trying to get my tach working. I have a problem with the CD.

There is no output from Td pin on the CD. I opened it up and also measured from the TD spot on the circuit board. Still no signal.

ACtually, I get 0.09V output but its supposed to be a 30%duty cycle 12V squarewave. I calculate this about 2.6V when measured RMS on DC out for my DVM.

Who has a schematic for the CD unit so I can trace this output?

Any suggestions for where to start?

[Grady Clay]

Jamie,

The engine runs OK but no tach?
Where are you measuring?
Can you set your DVD to AC P-to-P? That should read 12V+/-.
I assume you looked over the entire circuit board for bad solder joints, broken traces, or distressed components.

Try working your way back from the TD connection, checking components.

Best,
Grady

[jpnovak]

the engine runs fine except for some timing issues.

I am measuring the output at Td on the 6-pin CD to ground. I get no signal on V(AC) either. I do not detect any bad joints or otherwise problems on the board. I wonder if there is a fried resistor or cap somewhere. The donor was hit hard up front to total the car. It suold not surprise me if there was some other internal problem.

I guess I need to find local donor to swap CDs before I go further.

How do you take the board out of the CD? I did not want to break a wire tugging on them. Something is screwed to the housing and a glued connection on the front side.

[jpnovak]

new week. to the top.

[dukhunter20]

I wanted to bump this thread, I am having the exact same prob. No signal from the box, and I also am unsure how to take the circuit board out.

[rick-l]

if you go here (6-pin CDI ) you will see the TD output has a diode in series with it so it will source no current.

If you hook it up to the tach or a suitable pullup resistor (I'd guess 5-10 k) to 12V you may see an output.



edit; Ooops I take that back. I don't know what the TD ouptut should look like.

[rick-l]

I was curious how this worked. I don't know if this right or not.





What in the world does the Tach circuitry look like?

Linear Technology SPICE is fun to play with and its free.

[jimmcc]

Originally Posted by rick-l

I was curious how this worked. I don't know if this right or not.





What in the world does the Tach circuitry look like?

Linear Technology SPICE is fun to play with and its free.

I just finished answering a tach question in the 930 section and then started scanning for a tach schematic. Have one?

To answer your question, the tach has a pullup to 6 volts that the CD unit then takes to ground. They for some reason made the tach function like it was driven from points where the negative transistion and not a pulse triggers the counter.

Jim

[80-911SC]

until the third post i thought you guys were kidding the i really thought you were talking C ompact D isc player and D igital Video D isc, keep reading thinking it was a who's one first , what on second type of banter with an end result.

keep reading , now just confused with a headache ... thanks guys , i think

[ischmitz]

Rick is correct: Use a 2kOhm pullup resistor between TD and +12 Volts. You should see a perfect square wave on the oscilloscope. A DVM will not be suitable here. Without pullup resistor you won't see much.

Ingo

[T77911S]

the board is very hard to get out. the wires are usually crimped in the terminals so you have to heat them up and spread the middle"finger". imagine holding 3 fingers up like you are a boy scout, the wire goes between your fingers then the middle one is sometimes squeezed against the wire. if you put too much heat for too long, the whole pin comes out. not too big a deal, you just have to re solder it when you get the board out. the wires are not very well colored so keeping track of where the wires go is a little hard until you have taken a few apart. the board does have labels by the terminals, but you just have to understand where the wires are coming from. get a good solder sucker and 3 hands.

i have never done it this way but i suppose you could leave the wires on the terminals and just pull the terminals out and hope they solder back in good when you put them back.