Power Supply TEKTRONIX TDS340A ZYTEC 22917399 - Page 1
Forum section: electronics / repair

author: Mr Lurpak
author_rank: Contributor
timestamp: January 23, 2025, 10:31:10 pm
content: Hi I have a TEK TDS340 with faulty power supply ZYTEC 22917399.Unfortunately my service manual/schematic does NOT cover the POWER SUPPLY. I have 4 component missing/burned/blown out (when I bought it).U3: is this LM393P as the others on board or anyone knows what this is? 80% sure it is LM393 P/NQ5: Large transistor (mos fet I guess) value? *This is blown and can't read any text on casingVR9: Zener diode value??? *This is blown and can't read any text on casingand the LARGE CAP is 450V but cant find the uF value. (update as I found a picture in a blog this is 470uF/450V)I have uploaded a photo (I found on the internet) to help locate the parts. IF anyone knows of where to find schematics for Power Supply TEKTRONIX TDS340A ZYTEC 22917399?My hope is that some else has a repair project going on (TDS320/340/360) and don't mind having a look at the component values!!! - I think finding a scematics might be a bit optimistic as 3rd party PS. Despite I found schemtics for the other boards - but NOT power supply.Cheers

author: Smoky
author_rank: Frequent Contributor
timestamp: January 23, 2025, 11:09:37 pm
content: A little off topic but on a TDS420, there was a primary on/off switch on the back of the scope. The front panel of the scope has a power switch too but I read that if you just turn the front panel switch off you're really just putting the scope into "standby" mode because the power supply is still running and under power.On the TDS340, I don't see that power switch on the rear panel. Is it possible that the power supply in the TDS340 is put into "standby" mode the moment the power cord is plugged into the wall?After fixing a couple of these scopes, I never leave them plugged into the wall when they're not being used.

author: PwrElectronics
author_rank: Regular Contributor
timestamp: January 24, 2025, 01:48:34 am
content: Was this made in the mid 90s? If so, I was working as a product/test engineer at the plant where this was likely made. Unfortunately, I was not assigned to this product line but Tek supplies were made in the plant, although this one does not look familiar (and its been ~30yrs ago).In general, Zytec used a lot of Unitrode switching regulator ICs in that era. Looks like your bad parts are all on the AC input rectifier/filter/primary side of the SMPS. There may be a power factor correction circuit there as well.

author: Mr Lurpak
author_rank: Contributor
timestamp: January 24, 2025, 07:59:18 am
content: My tech problem here is ONLY to find value/replacements for the components that I am unable to read value of. I have not even gone to power up yet. - Looks like a lighting damage or it literally blew up as several component burn/blew the casing.So very specific on parts replacements. However, every info helps and I am sure it will still require more trouble shooting after replacment of these components.Cheers

author: Mr Lurpak
author_rank: Contributor
timestamp: January 24, 2025, 09:52:58 am
content: OK, a bit of OSINT and looking at pictures from related content I managed to find most (I hope and guess) values based on people posting pics.only main issue is the ZENER DIODE.VR9: Zener diode value???*This is blown and can't read any text on casing.Also, I read someone accidentially blew their PS and mentioned a BUZ355 - does this sound likely to be the main MOSFET on this power supply? anyone ever fixed or replaced one?Cheers