GW Instek GSP-827 - Page 1
Forum section: electronics / repair

author: tombi
author_rank: Regular Contributor
timestamp: February 10, 2017, 12:39:59 am
content: Hello,I got a new project! I went all Signal Path and bought a broken spectrum analyzer (relatively cheaply). Ok I have somewhat less skills than Shariar. Oh and there are no service manuals for this thingIt's got a couple of problems - I get no trace when I put in an RF signal and also half the screen is garbled. I thought I would go after the screen problem first as then I can see what I am doing!.I initially thought it was just the hot-bar attachments onto the LCD and I started re-flowing these. This didn't change much and then I noticed that the last digit of the date at the top of the screen is often wrong (i.e. a < symbol).That makes me think the screen is fine but the signal generation for the screen is not.Here is a shot of the screen with the fuzz on the bottom half. Note the last character in the date (middle top)https://photos.google.com/share/AF1QipNRvJEpkFLPn_ie7yjEtUo897Zp_c_2b0hRz8QOzUBK2gs7b5piEds9YSCdcb6uQQ/photo/AF1QipMb8pIsBS8xdeLd-0t5nRU-axI_Z4XRel-je0C_?key=ZThQZGtBQndKSVpNY0RfQWtRZ01NSFBpcFpHU093This is the main boardhttps://photos.google.com/share/AF1QipNRvJEpkFLPn_ie7yjEtUo897Zp_c_2b0hRz8QOzUBK2gs7b5piEds9YSCdcb6uQQ/photo/AF1QipNyhb4dSk70JZZDNWZxcMLUw1w82R_J1oxLOHay?key=ZThQZGtBQndKSVpNY0RfQWtRZ01NSFBpcFpHU093The LCD connector is at the far left.The chip top left is a LVTH16245 bus transceiver and all the LCD signals go through that. I think the EPSON D1370500A1 is what drives the LCD and its connected to the Cypres CY62137VLL-70Zi SRAM.I have half-a-mind to replace the SRAM but wanted to know what you think. It will be at least a couple of weeks until I can get a replacement. Can you think of a way of identifying if it is the main board or the LCD? I think if I look at the LCD signals it won't tell me much. I have a decent MSO to work with.The unit was ex-TAFE. Tafe did a partial repair and wrote it off. There was a note on the outside saying 'R15 burnt out (missing) and C48 replaced'. I think these are in the switching converter circuit on this board somewhere.BTW the build quality of the box is awesome - lots of ferrites, threaded screws into machined holes, metal inserts into plastic for screws. Really nice encoder and keys on the panel. I suspect its pretty slow and the phase noise not awesome but I bought it to play with mostly.Other interesting bits - it has the TG option!! And it works (I can see it on my scope at low frequencies). Also I can see 10MHz ref signal out the back. I can see the top half of the diagnostics page that says both LOs are locked (so that's good!). Hopefully just something in the front-end dead. All the software functions I have tried (that I can see) seem to work so the firmware is pretty much intact.Thanks,Tom

author: tombi
author_rank: Regular Contributor
timestamp: February 10, 2017, 01:17:21 am
content: Ok wait - the Epson chip is a S1D13700 and contains integrated Video RAM and character generator ROM.https://www.crystalfontz.com/controllers/Epson/S1D13700/82So its probably the LCD controller?

author: tombi
author_rank: Regular Contributor
timestamp: February 10, 2017, 01:42:41 pm
content: Ahh! Now I'm even more confused. If I lower the LCD contrast then the noise at the bottom of the screen disappears way before the graphics/text - so maybe the LCD is faulty?