| Author |
Message |
macgyver655
Joined: 22 Aug 2007
Posts: 8508
|
| Posted: Thu Mar 27, 2014 1:13 pm Post subject: |
|
|
Are you testing in circuit, out of circuit or both?
What is the part number on those?
|
|
| Back to top |
|
 |
AFryia
Joined: 09 Mar 2006
Posts: 965
Location: S.E. Michigan VPH-G70Q
|
| Posted: Thu Mar 27, 2014 11:28 pm Post subject: |
|
|
All are out of circuit. I'm testing IRFP250N (511L EO 55)
_________________
My Volt Blog
|
|
| Back to top |
|
|
macgyver655
Joined: 22 Aug 2007
Posts: 8508
|
| Posted: Fri Mar 28, 2014 12:52 am Post subject: |
|
|
Set DMM to diode scale. FET laying flat with pins towards you. Left to right is G,D S.
Put neg probe on D and pos probe on S.
It should read either somewhere around .5 or around .1
Take neg probe and just touch G for 1 second and then back to D and note reading.
Then take pos probe and touch G for 1 second and then back to S and note reading.
If you keep going back and forth your readings should also switch back and forth.
This is the FET switching.
If there is no switching or most legs just read close to zero then it is no good.
|
|
| Back to top |
|
|
AFryia
Joined: 09 Mar 2006
Posts: 965
Location: S.E. Michigan VPH-G70Q
|
| Posted: Fri Mar 28, 2014 9:35 pm Post subject: |
|
|
" FET# 1 2 3 4 5 6 7 8"
" drain to source .740 0 .736 0 .739 .737 .734 .735"
"G- drain to source .745 0 .742 0 .742 .742 .742 .742"
"G+ drain to source .320 0 .274 0 .279 .266 .274 .267"
So # 2 & 4 are toast. Can I assume the rest are fine?
What kind of tolerance can one expect. Is #1 borderline?
|
|
| Back to top |
|
|
macgyver655
Joined: 22 Aug 2007
Posts: 8508
|
| Posted: Fri Mar 28, 2014 11:23 pm Post subject: |
|
|
Well if it was me, and the replacement parts were fairly cheap, I would probably replace 1 also but I would not trash it. If the parts were pricey then it would be ok to use.
Also check those zener diodes in the power supply. They are also known to blow.
|
|
| Back to top |
|
|
AFryia
Joined: 09 Mar 2006
Posts: 965
Location: S.E. Michigan VPH-G70Q
|
| Posted: Sat Mar 29, 2014 6:16 pm Post subject: |
|
|
| macgyver655 wrote: | Well if it was me, and the replacement parts were fairly cheap, I would probably replace 1 also but I would not trash it. If the parts were pricey then it would be ok to use.
Also check those zener diodes in the power supply. They are also known to blow. |
Will Do!
Thanks for the help, it's really appreciated!
|
|
| Back to top |
|
|
macgyver655
Joined: 22 Aug 2007
Posts: 8508
|
| Posted: Sat Mar 29, 2014 8:00 pm Post subject: |
|
|
Your welcome. 
|
|
| Back to top |
|
|
AFryia
Joined: 09 Mar 2006
Posts: 965
Location: S.E. Michigan VPH-G70Q
|
| Posted: Thu Jun 05, 2014 11:07 pm Post subject: |
|
|
back again;
For a FET mounted to a large heat sink do you apply the thermal paste to both sides of the mylar insulator (FET>>mylar, maylar>>sink)?
_________________
My Volt Blog
|
|
| Back to top |
|
|
macgyver655
Joined: 22 Aug 2007
Posts: 8508
|
| Posted: Fri Jun 06, 2014 2:13 am Post subject: |
|
|
|
A very, very thin coat on all mating surfaces, almost transparent, will suffice.
|
|
| Back to top |
|
|
chinslip
Joined: 08 Jun 2014
Posts: 1
|
| Posted: Sun Jun 08, 2014 11:47 am Post subject: |
|
|
Hi guys...I'm new here. If been searching madly to find some kind of online help as my BKA 4A as also bought the farm. I know absolutely nothing about electronics but I know what a bubbled cap looks like and looks like I have about 8 of those. My dad was a TV repair man from the 60's to the mid 90's and I've seen many schematics. I can't read them but my dad can. Has someone managed to get their hands on a schematic?? I may be able to convince my 75 year old dad to pull out his old soldering gun.
thanks Norm
|
|
| Back to top |
|
|
Curt Palme
CRT Tech
Joined: 08 Mar 2006
Posts: 24396
Location: Langley, BC
TV/Projector: All of them!
|
| Posted: Sun Jun 08, 2014 2:57 pm Post subject: |
|
|
Hey Norm, welcome to the forum! Not sure if the schematics are out there, probably not, as companies either release them freely, or hold onto them like they're the best thing since sliced bread. <rolleyes>
Post a pix of the caps (you probably need 5 posts, so go down to the post testing area and post 4 more times). There's a difference between bad caps and ones that have the plastic top bubbled up a bit due to age (which can happen on larger caps without being bad).
what is the amp doing? Any power? No power?
|
|
| Back to top |
|
|
AFryia
Joined: 09 Mar 2006
Posts: 965
Location: S.E. Michigan VPH-G70Q
|
| Posted: Sun Jun 08, 2014 10:37 pm Post subject: |
|
|
I have the schematic specifically for my Amp version as there were a few. But unfortunately no BOM.
If you email Guitmer with your SN they should forward you the schematic for your amp. At least up till now they have.
_________________
My Volt Blog
|
|
| Back to top |
|
|
|
|
