Help Reverse Engineering Simple control circuit on Hitachi Plasma Logic Board - Page 1
Forum section: electronics / repair

author: canadaboy25
author_rank: Regular Contributor
timestamp: January 28, 2021, 09:56:31 pm
content: Hey everyone,I am working on a Hitachi plasma that will not power on. According to the service manual, two enable signals should be present from the main board in order to enable the PSU. However, I am only getting one enable signal. The main board is receiving all of the standby voltages it requires but it is just not outputting the second enable signal.I have followed the signal back to the small area shown in the attached image. However, since SMD component markings are pretty much useless, I am unsure what the two components pictured are doing. They are labelled "R33" and "G8WB" if that helps at all.I have added some markings to identify the ground pins. The via marked as PSU enable is the output going to the connector for the PSU that I am missing. This is a multilayer board and I haven't yet been able to track down where the top left pin of "R33" or the top right pin of "G8WB" goes. I would suspect they are just transistors but I am unsure of exactly what they are since they have 5 pins.Also, the thin trace that runs under "G8WB" and through a 0 ohm link, connects to pin 31 of a CY22391 clock generator chip which is the frequency select pin on the chip.Any help is appreciated!

author: RomDump
author_rank: Regular Contributor
timestamp: January 28, 2021, 10:29:31 pm
content: Quote from: canadaboy25 on January 28, 2021, 09:56:31 pmI don't know if this will help.

author: canadaboy25
author_rank: Regular Contributor
timestamp: January 28, 2021, 10:44:04 pm
content: Quote from: RomDump on January 28, 2021, 10:29:31 pmVery helpful!I don't suppose you'd be willing to share the entire document you took that snippet from?Thanks!

author: RomDump
author_rank: Regular Contributor
timestamp: January 28, 2021, 10:51:39 pm
content: Quote from: canadaboy25 on January 28, 2021, 10:44:04 pmYou said, you had the service manual for this TV. I just googled "Hitachi IG04" and Hitachi L37X01E popped up. I then googled "Hitachi L37X01E "service manual"" and downloaded the manual from one of the links. No idea what Hitachi model you are fixing.

author: canadaboy25
author_rank: Regular Contributor
timestamp: January 28, 2021, 11:22:43 pm
content: Quote from: RomDump on January 28, 2021, 10:51:39 pmHmm, very strange. I am working on a P45H4011 and the service does not include any schematics for the main board. I looked up the service manuals for two other Hitachi plasma's I have and neither did they.Maybe the L37X01E will be similar enough to help me figure something out.

author: fzabkar
author_rank: Super Contributor
timestamp: January 28, 2021, 11:36:01 pm
content: https://elektrotanya.com/hitachi_l37x01e_no_0237e.pdf/download.htmlhttp://www.smdmark.com/en-US/search/code?id=r33http://www.smdmark.com/en-US/search/code?id=g8w

author: RomDump
author_rank: Regular Contributor
timestamp: January 29, 2021, 01:33:02 am
content: Quote from: canadaboy25 on January 28, 2021, 11:22:43 pmA closer model. Google "Hitachi P50T01E "service manual"" similar schematic to L37X01E but plasma. Most companies use same boards in multiple devices.btw: fzabkar posted the chip datasheets. Same part numbers in the snippet. R33 is Toko 3.3V LDO and g8w some delay circuit.

author: canadaboy25
author_rank: Regular Contributor
timestamp: January 29, 2021, 06:18:25 am
content: So it turns out that the Power2 enable signal is generated by a EPM240T100C5N CPLD. I expected it to be generated by the M306H5FGFP microcontroller that the Power1 enable signal is generated from. The circuit I was looking at does not actually generate the signal, but rather uses it as an input. Since I am missing the signal entirely, it is irrelevant.I verified that the chip has power but it it just not outputting the enable signal. However, when I press the power button, nothing happens. The power button is connected to the microcontroller so perhaps the microcontroller is not getting an input that it wants so it is not enabling the CPLD.Is there any way to dump the ROM from the microcontroller or the CPLD? The datasheets for both of the chips are available.