UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio and TV Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > General Vintage Technology > Components and Circuits

Notices

Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

Reply
 
Thread Tools
Old 23rd Nov 2020, 6:02 pm   #1
Whaam68
Hexode
 
Join Date: Feb 2007
Location: Luton, Bedfordshire, UK.
Posts: 310
Default Understanding transistor tester readings

Well specifically are these devices testing as good or not?
First the background...around 2012 I built a diy class A kit amp the Nelson pass Amp Camp....one of the first amps I built. I brought it down from its 10 year resting place in a box in the loft on Saturday to use it in the spare bedroom (now my office). All was well and it sounded great. Stupidly I moved a speaker with the amp on and heard a bit of static and the channel driving that speaker died and the heating cooled rapidly. I removed the board from the duff channel and de soldered the two output mosfets and the other mosfet and transistor. I had recently picked up a cheap transistor checker and it is recognising the n channel mosfets. If anyone can confirm the readings seem ok or not it would be appreciated as a start in my figuring out what went wrong. The outputs are IRFP240 the ďdriver?Ē Is a 2sk170 jfet and there is a ztx450 transistor.
Thanks
Mike
Mods please move if this is in the wrong section! Thx
Attached Thumbnails
Click image for larger version

Name:	0998A04C-5FDC-4219-B3E1-8AFD4F09E0FF.jpg
Views:	92
Size:	32.4 KB
ID:	221112   Click image for larger version

Name:	13F20A95-08CF-4AD4-87DA-A6BEDBC77F86.jpg
Views:	78
Size:	60.8 KB
ID:	221113   Click image for larger version

Name:	E164BC13-E2A9-46B8-A338-D0C42DDC8F5E.jpg
Views:	74
Size:	80.7 KB
ID:	221114   Click image for larger version

Name:	35B5BBE3-1B4D-4231-8A50-40A712C7188B.jpg
Views:	78
Size:	75.5 KB
ID:	221116   Click image for larger version

Name:	FBB27FFD-636B-4E73-B11C-1A93094989FF.jpg
Views:	61
Size:	72.6 KB
ID:	221117  


Last edited by Whaam68; 23rd Nov 2020 at 6:19 pm. Reason: Wrong section?
Whaam68 is offline   Reply With Quote
Old 23rd Nov 2020, 7:58 pm   #2
MotorBikeLes
Octode
 
Join Date: Dec 2012
Location: Kirk Michael, Isle of Man
Posts: 1,656
Default Re: Understanding transistor tester readings

If they are in the order you listed them, first two probably OK (somebody may disagree), the third looks OK, a MOSFET with a diode across source to drain, the final one looks like two diodes (which a transistor CAN look like), but it rather looks like a dead transistor to me. Not sure without getting a book out, but I think the ZTX450 may well be a pnp transistor. Get one and see what that shows on the tester, different I am sure, with a proper identification given.
Les.
MotorBikeLes is offline   Reply With Quote
Old 23rd Nov 2020, 8:03 pm   #3
paulsherwin
Moderator
 
paulsherwin's Avatar
 
Join Date: Jun 2003
Location: Oxford, UK
Posts: 20,889
Default Re: Understanding transistor tester readings

ZTX450 is a medium power NPN transistor - pretty standard bipolar driver in a power amp.
paulsherwin is online now   Reply With Quote
Old 23rd Nov 2020, 8:08 pm   #4
buggies
Heptode
 
buggies's Avatar
 
Join Date: Jan 2009
Location: West Lothian, UK.
Posts: 536
Default Re: Understanding transistor tester readings

Certainly should not be Emitter - Collector 0.08 Ohms.
Where's me Avo...
__________________
George
buggies is offline   Reply With Quote
Old 23rd Nov 2020, 9:07 pm   #5
Whaam68
Hexode
 
Join Date: Feb 2007
Location: Luton, Bedfordshire, UK.
Posts: 310
Default Re: Understanding transistor tester readings

Thanks all and for clarity pic 1 is the 2sk170 jfet
Pics 2&3 are the same IRFP240 MOSFET (havenít se soldered the other yet)
Pic 4 is the ztx450...the cheapest part by far to replace.

De soldering the mosfets was a pig as the board is high quality which is why Iím keen to figure out their condition before re fitting.

The full circuit if anyone is interested is on page 5 of this short paper.

http://www.firstwatt.com/pdf/art_amp_camp_1.pdf

At the mo the consensus seems to be the ztx might be iffy. At least itís by far the cheapest part to replace not that any of these are that pricey...I just ordered some spares.
Attached Thumbnails
Click image for larger version

Name:	7DD08DB5-E841-496B-88DA-BE65F7BDE6D3.jpg
Views:	35
Size:	71.7 KB
ID:	221128  

Last edited by Whaam68; 23rd Nov 2020 at 9:33 pm. Reason: Add a pic
Whaam68 is offline   Reply With Quote
Old 5th Dec 2020, 8:25 pm   #6
Whaam68
Hexode
 
Join Date: Feb 2007
Location: Luton, Bedfordshire, UK.
Posts: 310
Default Re: Understanding transistor tester readings

Just to thank everyone for the guidance. The ztx transistor on the one channel was correctly ID ‘d as suspect but turned out to be the only thing blown. I de soldered all including the outputs checking with a multi meter after finding a very thorough YouTube tutorial. I fitted a replacement last week and the amp is singing perfectly again.

Last edited by Whaam68; 5th Dec 2020 at 8:47 pm.
Whaam68 is offline   Reply With Quote
Reply

Thread Tools



All times are GMT. The time now is 11:20 pm.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2021, vBulletin Solutions, Inc.
Copyright ©2002 - 2020, Paul Stenning.