Help with K7000 Hot

MKplayer1start

New member

Donor 2011
Joined
Dec 10, 2009
Messages
1,207
Reaction score
11
Location
Toronto, Ontario, Canada
hey guys,

I got this K7000 popping fuses so I got a Bob Roberts K7000 kit and replaced all the caps, Flyback, and the Hot. Still popping fuse right away. I suspect the Hot. first of all, the hot that comes in the Bob Roberts Kit has legs that are too short. I had to drill a new hole in the heatsink so I could lower the new hot enough to solder the legs. I didn't think that would be an issue but maybe I'm wrong and that's my problem?

I checked the hot with a dmm (Set the dmm to 200k) and I get a reading of 1.4

does that mean a low reading and shorted? or should I set the dmm to 20k?

any help much appreciated, I was gonna send it out for repair, then things got crazy at work and now I got a little free time and I think I can fix it with the help from you guys.
 
Last edited:
from the faq it looks like I should check the voltage regulator and maybe C36 cap.

can anybody tell me the location of the Voltage Regulator? and how to test?
 
Alright, I'll try to explain it to you the best I know. Basically, the fuse blows when you have the ground shorted to the voltage. If you look at the bottom of that entire area, the ground is basically the edge where the frame is, and there's a huge fat 'river' trace that runs up under the area the hot is in. Anything that touches that, and the other traces, but is shorted, will blow your fuse.

Things that fit the bill.

Flyback
HOT
Voltage Regulator
Any of the huge caps behind the Hot
Any of the diodes in the power section

The voltage regulator is in the corner, bolted to the side of the frame. If you look on the bottom, you'll see that one of the legs is connected to the ground of the board we were talking about. If you check resistance between that ground leg, and all the other legs, if it's shorted, one of those will be shorted and bad. You may remove it from the board, and it's fine, but something else is shorted on the board giving you a bad reading.

Any of those large mylar caps could be shorted, you could remove them one at a time and test them to see if they are connected end to end, if so they're shorted.
 
Alright, I'll try to explain it to you the best I know. Basically, the fuse blows when you have the ground shorted to the voltage. If you look at the bottom of that entire area, the ground is basically the edge where the frame is, and there's a huge fat 'river' trace that runs up under the area the hot is in. Anything that touches that, and the other traces, but is shorted, will blow your fuse.

Things that fit the bill.

Flyback
HOT
Voltage Regulator
Any of the huge caps behind the Hot
Any of the diodes in the power section

The voltage regulator is in the corner, bolted to the side of the frame. If you look on the bottom, you'll see that one of the legs is connected to the ground of the board we were talking about. If you check resistance between that ground leg, and all the other legs, if it's shorted, one of those will be shorted and bad. You may remove it from the board, and it's fine, but something else is shorted on the board giving you a bad reading.

Any of those large mylar caps could be shorted, you could remove them one at a time and test them to see if they are connected end to end, if so they're shorted.

thanks I'll start checking everything suggested
 
try theses parts as well.

C 36, 37, 38 or ( 39 if this model has it) could have gone bad.
the H.O.T. could have took a shit.
any one of D 13-24 could have failed.
the fly went bad.
the VR totally shorted out.

theses are some of the usual things that will make the fuse blow.

check all of them for shorts and see what you come up with.

Peace
Buffett
 
Thanks guys for all the info. Probably gonna work on it tonight. Lucky I have a working K7000 on my bench I can compare readings on. Will check everything

Ken - Yes I made sure I used the thermal grease and mica insulator. But I will re-do it if the hot isn't shorted. I read on here some people don't even use thermal grease and have no issues? Weird
 
I recently ran across a K7000 that gave me a shorted HOT reading - until I pulled it out and it was no longer shorted. Put it back in and it wasn't shorted. powered up and blew the fuse and it was shorted again. Pulled it out and it wasn't shorted. Repeat.

C36 turned out to be the culprit. Even though it wasn't measuring as shorted, as soon as you powered up it went to a short state until you removed something from the circuit (with power off of course). Replacing the C36 fixed that problem. HOT was still good, btw.


But in your case, if the HOT and VR check as good, the next most likely culprit is C38...
 
Well I took readings of everything still attached to the chassis and looks like the VR is shorted, Hot is shorted, and diodes 19-22 are shorted.

However like modessitt said, I'll pull everything out 1 at a time and take a reading of them while they are out and see if they are actually shorted.

just to make sure I'm doing this right, I have my DMM set to 200ohms is that correct?
 
if your checking diodes you have a diode setting on you DMM. if your checking for shorts you have a continuty setting for that. sometimes diode and continuty are the same on you DMM sometimes they are their own setting depending on your model.
 
Last edited:
this is what I got:

d51a27cb.jpg


is this the setting to use if I want to check for shorts?
 
you are going to want to use the lowest setting to test for shorts "200" ohms. if shorted it will read 00.0 or 00.1. I recommend upgrading your DMM, makes life easier if you do alot of this type work. get one that beeps at you when there is a short.
 
you are going to want to use the lowest setting to test for shorts "200" ohms. if shorted it will read 00.0 or 00.1. I recommend upgrading your DMM, makes life easier if you do alot of this type work. get one that beeps at you when there is a short.

Thanks will pick one up tomorrow that is better for continuity
 
Had to drill a lower hole? This is news to me. Dumb question but are you sure you arent stuffing a hot into where the vreg goes? Evwen if not, dud you use a mica insulator? Check all your diodes yet?
 
Had to drill a lower hole? This is news to me. Dumb question but are you sure you arent stuffing a hot into where the vreg goes? Evwen if not, dud you use a mica insulator? Check all your diodes yet?

Not a dumb question, but yes I'm sure I replace the hot with a new hot in the right place. I used thermal paste, mica insulator, and thermal paste again. The new hot I got had really short legs though.

I will pull everything off the board and test again with a dmm that is better suited for continuity.
 
Just to help you: Since the ground connects to all the stuff we're talking about, if any 1 of those is shorted, they'll ALL test shorted on the board (which is what's going on with yours). So you need to pull one off, and keep testing the board to see if it's shorted until whatever you pulled off, leaves the board testing not shorted. Start with the HOT.
 
1) sounds like you were putting a 5-leg HOT in a 4-leg slot. If you paid attention to your old one, you'd see that 5th leg was cut off and not used. Or your trying to replace an STR3130 with an STR30130, which aren't the same thing.

2) if D19-22 are shorted, then this chassis was (or is) powered up without an isolation transformer, which would explain blowing fuses and other stuff...
 
The hot is 3 legs.

The STR30130 is the VOltage regulator no?

The history of the chassis is that it was in my friend's MK cab working and definately was using the original ISO in the cab. He said it stopped working so I swapped it out and installed a working chassis for him.
 
Okay, I just reread your note about drilling a hole (now that I'm awake), and I understand what you meant. Usually there is a lower hole already for a replacement with shorter legs, but as long as the insulator is used, that should be fine....
 
okay I got a new DMM that has more functions. Diode, Resistance, and Continuity (with Beep)

when checking for shorts I set it to continuity? I pulled out my hot and with the DMM set to continuity it beeps on the 2 outer legs, but doesn't beep with 1 outer leg and middle leg.

does that mean it is shorted?

is this the proper way to test a Hot, and can I test the VR the same way?
 
Back
Top Bottom