Sharp XM1801 - B+ takes a nose dive after a few minutes

blkdog7

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Sharp XM1801 - B+ takes a nose dive after a few minutes

I have a Sharp XM1801 in my RED TENT that has fresh caps, filter caps, HOT, and a new flyback. I have double and triple checked my work. However, I have some odd B+ issues. I don't think it's the B+ pot. But, not positive.

I set the B+ to 108v and the monitor is perfect. Then, after a few minutes, sometimes 10 or 20, the B+ drops to 50v or somewhere similiar and the monitor shuts down. I hear this click click click sound coming from the flyback area when it does this. I see no arcing or other similar stuff. Did I get a bad flyback? What else would cause the B+ to nose dive? I have a second repro flyback I could try. Just getting really sick of taking this monitor apart!!! :)

Any ideas?
 
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HI John,

I have not worked on 100's of red tents to know your scenario as for instance the g07 or k7000..
I would never look at a NEW flyback replacement as the cause of a problem first. I wouldnt worry about that just yet.
There are a many other things that can cause you issue from a power supply section of your monitor to horizontal driving.

If it helps you feel better another customer was wondering if his red tent flyback was bad.. was not the case in the end he sent the replacement I fronted him back to me. Sounds like it was the same problem you are having now. Turned out not to be my red tent flyback at all as the problem.

Conversation bits:
"I don't know if you remember this transaction, but awhile back I borrowed a Nintendo red tent flyback to possibly check and see if one of my purchased replacements was defective. I just got around to trying it out, and it turns out that my flyback is not the culprit, but something else is....Just giving you a heads up and letting you know I'm returning your replacement . I'll also include cash to cover the original replacement shipment.
"

"Greetings Chad,

I don't know if you remember this transaction, but awhile back I borrowed a Nintendo red tent flyback to possibly check and see if one of my purchased replacements was defective. I just got around to trying it out, and it turns out that my flyback is not the culprit, but something else is....Just giving you a heads up and letting you know I'm returning your replacement . I'll also include cash to cover the original replacement shipment."

Good luck.
Thanks.
Chad.
 
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A bad repro fly won't drop like a rock. Suspect your REG or your IC601 equivalent to be failing causing your shut down.

Yes Chad, it would appear that there may be some bad repro flybacks out on the market.
 
A bad repro fly won't drop like a rock. Suspect your REG or your IC601 equivalent to be failing causing your shut down.

Yes Chad, it would appear that there may be some bad repro flybacks out on the market.

What is the REG?

Does the XM1801 have an IC like the 20EZ does? Where is it?

What about that clicking noise? Odd?
 
What is the REG? I701 is the reg and SCR701 is the power out

Does the XM1801 have an IC like the 20EZ does? Where is it? Yes, located just above the B+ pot close to the BJ / TP

What about that clicking noise? Odd? HV Shutdown

Answered above in the quotes. The XM1801N is just like the 20EZV, and they are notorious for crapping out the yokes.
 
Answered above in the quotes. The XM1801N is just like the 20EZV, and they are notorious for crapping out the yokes.

Ok, cool. Thanks!

I have a parts board coming from Bob Roberts along with a B+ pot. I'll try swapping out the REG and the IC too from the parts board. Do they make those parts new?
 
Which part numbers are the reg and IC? Anyone know? Gonna tackle this before the weekend.

Cheers.
 
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Well, I fixed this. Just thought I would share what I did...

The monitor got a cap kit, new HOT, and new flyback. STILL was going into HV shutdown. I would often get a ticking sound during the shutdown. During shut down (no picture on screen) my voltage would drop to 50v and then freak out and go from 50 to 60 to 70 to 60 to 80 to 90v, etc. Prior to shutdown, the monitor would usually work fine for 10-15 minutes or longer and then just shut down. Sometimes it would run for less than a minute. Sometimes it would work for up to an hour before shutting down. I was able to dial in the B+ to 110v with no problem. It was fairly steady and would hold around 110v until shut down.

Next, I replaced the B+ POT, I601 chip and the voltage regulator with parts from a donor chassis.

STILL was going into HV shutdown.

So, I checked to make sure my tube didn't have a short with my sencore tube rejuver/analyzer. No shorts. Ok, cool.. tube is good.

Now, I was stuck...

Well, I thought maybe it was the new flyback. So, I replaced it with another I ordered from Chad.

Wrong! HV shutdown still.

Then..

I decided to replace the HOT again AND I reflowed the solder all over the chassis board. Any joint that looked cloudy or just not shiny got reflowed. And, well, that and the new HOT fixed it (I did both at the same time). So, either I had a bad new HOT (not likely) or I had a bad solder joint. Either way, I am going to be reflowing solder joints more often on monitors when I am trying to get them working.

So, yeah, it works. Good luck future monitor repair forum searching people that find this thread. I spent 10 hours of my life fixing this damn monitor. I can now take one of these monitors apart in my sleep. I swear to god I must have taken this monitor apart 20-30 times. Ugh!
 
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Thanks. Will be ordering.

Kind of OT but related to my Red Tent issue -- can a monitor chassis malfunction cause a PCB to reset? I've changed the switching power supply and swapped PCBs but the reset is still occurring. Started happening after I capped one of the monitors (which is now shutting down). I've hit a brick wall with it.
 
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