ISO-TECH / GWINSTEK range - Oscilloscope Schematic - Page 1
Forum section: electronics / projects

author: gm0otb
author_rank: Contributor
timestamp: September 16, 2011, 08:57:28 pm
content: HI,My first post.. Woohoo!Just bought a ISO-TECH SRI658 from ebay, only had it on for 5 minutes and the trigger stopped working, apparently ISO-TECH is really GWINSTEK.After locating a schematic diagram (nightmare), the thing was up and running in no time.Thought I would make the Schematic available to anyone who needs it, just PM me, its too large to attach.Ray.

author: saturation
author_rank: Super Contributor
timestamp: September 16, 2011, 09:33:01 pm
content: Welcome! Was it something like this?http://www.ebay.co.uk/itm/ISO-Tech-ISR-50-MHz-Dual-Trace-Oscilloscope-/170675519695Glad you got it working, it looks worth repairing and fairly low cost. What was wrong with it?

author: gm0otb
author_rank: Contributor
timestamp: September 16, 2011, 10:52:24 pm
content: Exactly like that one.. lolReceived it and within no time the thing stopped triggering on "Auto" and "Manual", it would trigger on the "Ext" from the front panel, the bloke I bought it from was excellent, great com's and offered to send manuals etc.After chasing around the net for 2 days, found a diagram, the scope had popped a PNP transistor on the Trigger switch circuit , just before hitting the trigger amp section. I was lucky, easy fix.Happy days!

author: saturation
author_rank: Super Contributor
timestamp: September 17, 2011, 12:47:45 pm
content: Enjoy. In electronics, I find most fixing is easy, the harder part is finding the defect or the replacement part. That you got it quickly is excellent.Quote from: gm0otb on September 16, 2011, 10:52:24 pm

author: ptp170
author_rank: Contributor
timestamp: June 18, 2013, 08:11:35 pm
content: I know this is an incredibly long shot since the OP only has 10 posts since 2011 but if you have that manual or, even better, a photo of the location of the PNP transistor then I would love you all forever!Just got hold of an ISR622 with exactly the same issue and it would be great if I could fix it!Kind regardsChris

author: ptp170
author_rank: Contributor
timestamp: June 18, 2013, 08:56:43 pm
content: Think I may be getting somewhere....Downloaded the 'GOS_600G_60MHz.pdf' manual from this link..http://www.eserviceinfo.com/index.php?what=search2&searchstring=GOS+523%2F623.. am currently staring at the schematics on pages 16/17??Anyone like to take a punt on which PNP could be the likely cause??Kind regardsChris

author: SeanB
author_rank: Super Contributor
timestamp: June 19, 2013, 04:04:10 pm
content: Most likely Q401/2 are faulty, as they are on the input and can get cooked easily. Replace as a matched pair with 2 matched to be close in gain at least, so use 10 and choose 2 in the middle of max and min gain. 2SA838B can be found athttp://pdf.datasheetcatalog.com/datasheet/panasonic/SJC00005BED.pdfNothing special other than being a PNP 30mA 20V usable to 200MHz.

author: ptp170
author_rank: Contributor
timestamp: June 19, 2013, 08:24:18 pm
content: Hi SeanB,You are indeed correct. Ray (the OP) kindly emailed the fix as I had also been eyeing up Q401/Q402. I have replaced the two PNP's with a couple of generic ones I had lying around and IT WORKS!I have ordered two 2N3906's as this was the recommended replacement with the slight caveat being the Base and Collector need to be swapped over so I will swap then out when they land on my doorstep.Thank you to everyone and especially Ray for taking the time to email me back.Kind regardsChris