P538 K7191 Diode Numbers maybe a couple other questions

Broodwich

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P538 K7191 Diode Numbers maybe a couple other questions

Was wondering if i could get a confirmation on these numbers i got from diode checking the diodes on my P538 K7191 chassis here. It's been forever since i've been to electronics class and i'm getting 2 different answers when I search (one says open one direction and some small number the other, and the other says .400-700 one way and 1200 the other).

(Measurements in volts)

D16 1.150/.465
D17 Open/.465 (this one is in a burnt area and i'm guessing is bad)
D18 2.120/.479
D19 2.141/.512
D20 2.127/.516
D21 2.127/.516
D22 2.141/.508
D23 .538/.523
D24 .538/.523


Other questions:

-This chassis has a spot for a cap at C7 but looks to have been cut off. another p538 chassis i have doesn't have this location at all.... ???

-Is there a way to test the VR without having the chassis powered? (i must be blind not being able to find this...)
 
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they all look like good readings to me from memory.

if all else fails pull one leg of each diode and measure it.

one way it will read .400-.700 the other it will read open.


C7 needs to be there.

on some revisions it was soldered on the bottom of the chassis.
the later versions had a spot for it on the chassis.

Peace
Buffett
 
Thanks, tho that still makes me wonder about 17/23/24. I'm sure they're good but on the side of the large heatsink it says "NO High voltage" tho R97 was completely broken free of the solder joint.

C7 is definitely missing (not on the solder side) any idea's what it's value is? i didn't see it on modessitt's site/caplist (Edit: the sheet schematic I have say 022 under the C7 location).

also i did test the hot and it tested good at .478
 
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the 3 you are concerned about are fine.
i measured them to be sure on a chassis i have here.

C7 is non electrolytic and the value i have on one here reads 223J 100

it is a mylar cap the spec sheet says it is a .022uf 50v cap

on the 25" it seems to be a 100v cap.

Peace
Buffett
 
the 3 you are concerned about are fine.
i measured them to be sure on a chassis i have here.

C7 is non electrolytic and the value i have on one here reads 223J 100

it is a mylar cap the spec sheet says it is a .022uf 50v cap

on the 25" it seems to be a 100v cap.

Peace
Buffett

.022uf 100v looks like bob carries that (4) for $1.00 thanks for checking on that and the other diodes. Guess once i replace that mylar cap i could give it a test fire pre capkit/flyback to see if it even does anything...
 
i used to do a pre firing job to see when i was new to the repair gig, but after it was a 90% failure to a 10% work rate i never bothered to fire it up till after the check list i have and the rebuild and re flow is done.

i now have about a 95% success rate of the chassis working fine and only needs adjustment to be 100% after the rebuild.

this all depends if the customer said that there were other problems or not.

but on a complete unknown chassis i never bother till after the rebuild.

so i would not bother if it were me.

you could loose another fuse of smoke un smoked parts in the process.

Peace
Buffett
 
i used to do a pre firing job to see when i was new to the repair gig, but after it was a 90% failure to a 10% work rate i never bothered to fire it up till after the check list i have and the rebuild and re flow is done.

i now have about a 95% success rate of the chassis working fine and only needs adjustment to be 100% after the rebuild.

this all depends if the customer said that there were other problems or not.

but on a complete unknown chassis i never bother till after the rebuild.

so i would not bother if it were me.

you could loose another fuse of smoke un smoked parts in the process.

Peace
Buffett

so basically your saying cap it and cross my fingers? :D

personally i'm just worried about blowing $20+ in HOTs or VRs and i just want to knock down the amount of waste money as possible if that makes any sense. (normally i take the shotgun approach..)

I reflowed about 90% of the board (definitely hitting the standard trouble spots, as well as the neckboard).

I definitely appreciate the replies
 
if you measure everything for shorts before you fire up the chassis after the cap and fly, you will see if there are any major problems any way.

i have a 20+ part check list i go thru before i even cap and fly a chassis, ( no i am not going to list them out it has all been covered by me and others on here already:) ) this way i know the general condition of it and know what and where to focus my attention.

you do not have to shot gun anything if you measure all the problem parts first.

caps and fly are a must any way on a K7000 so start there and measure the rest before you fire it up.

Peace
Buffett
 
if you measure everything for shorts before you fire up the chassis after the cap and fly, you will see if there are any major problems any way.

i have a 20+ part check list i go thru before i even cap and fly a chassis, ( no i am not going to list them out it has all been covered by me and others on here already:) ) this way i know the general condition of it and know what and where to focus my attention.

you do not have to shot gun anything if you measure all the problem parts first.

caps and fly are a must any way on a K7000 so start there and measure the rest before you fire it up.

Peace
Buffett

That's what i'm trying to accomplish and avoid shotgunning every part. I've read through the sticky and done my search i've probably done 1/2 of what's on your list but there isn't a complete list that i've found yet. only partial things here and there, I've actually made the sticky my best friend and probably read over it 10-12 times (it actually could use some updating/more info (ex. testing the VR and the not so clear diode test instructions).

Personally i'd love to skip the flyback as well if possible as that's $20 more left in my pocket but even without cracking/yellow stuff leaking everyone still says just change it out.... kinda defeats the no shotgunning theory.

As I said, I do appreciate your replies!
 
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Heck, get the fly back, it will be used at some point.

oh there's no doubt about that, and i was going to get one anyways. I just didn't want to use it on this chassis if i don't need to (I think you and I both know i'm running on borrowed time on a couple of my other chassis with cracks and 1 with white knobs). One of those would be a much better suited recipient.
 
not even borrowed time really.

i treat theses the same as a G07 fly replace now or replace later with other parts.

so 20.00 of the top now or 20.00 and other parts when it goes.

also so what if it is bad now and you still smoke good parts. you still have to order a fly the new parts and pay more shipping.

do it once do it rite and game happy.

just my thoughts on the subject.

Peace
Buffett
 
not even borrowed time really.

i treat theses the same as a G07 fly replace now or replace later with other parts.

so 20.00 of the top now or 20.00 and other parts when it goes.

also so what if it is bad now and you still smoke good parts. you still have to order a fly the new parts and pay more shipping.

do it once do it rite and game happy.

just my thoughts on the subject.

Peace
Buffett

yea the more i'm looking at it the more i figure just do it. and yea i read about the fact that even the new one can come bad and smoke parts :( FML

So yea, this chassis just got a bath and is drying in my oven right now. I really just don't want to smoke a new fly or the existing good tested HOT.

any pointers on testing the VR without power?
 
use your diode test and if any combination of the legs are shorted it is most likely bad.

the big test is when you fire up the chassis and it is either running like it should or it is in HV shutdown.

if you get the correct B+ then your VR is good.

if you are in HV shutdown then pull one leg of D10 if the chassis comes back to life then your VR is most likely toast.

the good news is if your VR is bad only rare occasions will it smoke the fuse.

Peace
Buffett
 
hmm awesome, I've never fired this chassis personally. I bought it used off the bay as a spare/back-up/parts/whatever. The fuse in it was good although it said "No High Voltage" because i robbed it to test another chassis at one point i'll go test the VR right now sans power.

Personally i'm thinking the reason it had "No High Voltage" was due to c7 being missing and r97 having destroyed solder joints (causing the board to brown/burn a little in this area) R60's joints weren't that great either. I guess we'll find out after the flyback and other parts come in.
 
yea if you got it from the bay that is a no brainier to do the works.

yea R97 not being in there solid will cause it to shutdown along with R101.

you will not need C7 in there to see if it works or not but it will need replacing.

now if those parts were missing i would check it over really well as a parts chassis off the bay could have anything wrong/missing on them.

Peace
Buffett
 
yea if you got it from the bay that is a no brainier to do the works.

yea R97 not being in there solid will cause it to shutdown along with R101.

you will not need C7 in there to see if it works or not but it will need replacing.

now if those parts were missing i would check it over really well as a parts chassis off the bay could have anything wrong/missing on them.

Peace
Buffett

Just checked the VR and only got slight resistance (momentary beep from my fluke MM) from the middle pin to the one directly to the right of it (about 680ohm) all the other combinations were open

and R101 was also the other one with a bad joint and brown/discoloration below it. (here's a pic of the chassis being discussed).


My first chassis bath :D by Broodwich518, on Flickr
 
what does your yoke measure.

you have the alternate low impedance yoke chassis that wells made.

your yoke needs to measure between .5-2.5 and 5.5-7.5

i had one like yours that would not work on a standard yoke.

Peace
Buffett
 
Fml

what does your yoke measure.

you have the alternate low impedance yoke chassis that wells made.

your yoke needs to measure between .5-2.5 and 5.5-7.5

i had one like yours that would not work on a standard yoke.

Peace
Buffett

really??? is that what that little remote resistor/capacitor board is mounted to the frame left of the flyback? (mecha and i were wondering about that, and out of the 8 chassis/tubes i have i have 1 other like this one).

I'm not sure what the yoke measurements are on any of these unfortunately :( I hope you deduced that from the lil remote board as one of the other chassis i'm about to work on is the one with the same.
 
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