USB device not recognised (CY7C68014A woes)

Hosted forum for UMDK related questions

Moderators: BigEvilCorporation, prophet36

Post Reply
amushrow
Interested
Posts: 42
Joined: Mon Jan 02, 2017 12:56 pm

USB device not recognised (CY7C68014A woes)

Post by amushrow » Sun Mar 19, 2017 6:43 pm

I've been putting together a couple of boards but one of them is giving me jip.
One of them enumerates properly and the usb device shows up, the other does not.
There are no dry joints (that I could find, obviously). There are no shorts between any of the pins on anything anywhere, i've looked with a microscope and probed it with a meter.
I've replaced the CY7C68014A IC (actually I have CY7C68013A, but they're identical apart from power consumption it seems).

The only clue I have is that the oscillator doesn't seem to be running, I don't have a scope though so I can only see some voltages, but on the board that works the CLK testing point is at 1.6v (which makes sense I guess, if the meter is giving me an average) and in the one that doesn't it has 0v.
Pin 11 of the CY7C68014A has 3.3V (tested on the crystal's leg) but Pin 12 gets 0v.

If anybody has any insight it would be appreciated. I just can't find what's up with the bugger.

User avatar
prophet36
Very interested
Posts: 234
Joined: Sat Dec 13, 2008 6:58 pm
Location: London, UK
Contact:

Re: USB device not recognised (CY7C68014A woes)

Post by prophet36 » Sun Mar 19, 2017 7:46 pm

I have tried CY7C68014A and CY7C68013A, and both work fine, so your swap shouldn't cause problems.

Do you see the same behaviour if you remove the EEPROM links from both boards? Can you compare the levels on all pins, comparing the working board with the non-working board? That might give us a better idea. Aside from that, check that you put the right value capacitors and resistors in the reset circuit, the oscillator circuit, and the EEPROM circuit.

amushrow
Interested
Posts: 42
Joined: Mon Jan 02, 2017 12:56 pm

Re: USB device not recognised (CY7C68014A woes)

Post by amushrow » Sun Mar 19, 2017 10:45 pm

All voltages match on the boards, resistors are correct.
Quite by chance I've managed to replicate the behaviour on the working board. If I measure the voltage at the crystals leg and hold the probes long enough (5-10 seconds), that stops the crystal until the device is reset. The leg now shows as 3.3v, and the USB device in windows switches to an "Unknown USB Device (Device Descriptor Request Failed)" all the same as the non-working board.

User avatar
prophet36
Very interested
Posts: 234
Joined: Sat Dec 13, 2008 6:58 pm
Location: London, UK
Contact:

Re: USB device not recognised (CY7C68014A woes)

Post by prophet36 » Sun Mar 19, 2017 11:03 pm

I would try de-soldering the 22pF caps on the oscillator circuit and replacing them.

amushrow
Interested
Posts: 42
Joined: Mon Jan 02, 2017 12:56 pm

Re: USB device not recognised (CY7C68014A woes)

Post by amushrow » Sun Mar 19, 2017 11:25 pm

They've already been replaced.
Increasing the capacitance gets the crystal going but it's unstable. I'll have to pick up some different values and see what it needs.
The boards are identical though, I can only guess that the working board is just scraping by.

amushrow
Interested
Posts: 42
Joined: Mon Jan 02, 2017 12:56 pm

Re: USB device not recognised (CY7C68014A woes)

Post by amushrow » Wed Mar 29, 2017 8:31 pm

So I got an oscilloscope (always nice to have an excuse to buy some new gear), the crystal is oscillating fine (with the 22pf caps)
It seems that the reset pin is outputting 3.3v (which for sure is not supposed to happen) I disconnected the resistor at R2 to verify, and sure enough it's getting some juice from somewhere.

At some point I'll move the chip to a working board and see if it's damaged or there is just a short somewhere on this board (or both).

Post Reply

Who is online

Users browsing this forum: No registered users and 1 guest