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ArcadeMachinist

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Good day, masters!

I have recently aquired 2 nice Naomi Universal Cabs and one of them has weird monitor problems.
The picture is compressed when it is just powered on, but after a few minutes, when it warms up - it becomes so wide and tall that it does not fit the screen.
I have tried front panel adjustments, I can scale the picture while it is cold to look normal, but when it has warmed up - even if I turn the pots to shrink it to the minimum - it is still to big to fit.

Cold start:
tn_Sanwa_1.jpg

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Warmed up:
tn_Sanwa_2.jpg

Zoom in

Any ideas where to look at?
As it depends on cold-warm state of the tube - I suspect it is not just adjusments, but some failed components.

Also if anyone has understanding on CRT chassis <--> Tube matching, I would be grateful to hear.
I understand that yoke V&H resistance should match, but what else makes tube compatible with a given chasis?
 
I had a similar issue. It was the flyback going out. This said, start with cap kit. Caps are cheap, flyback isn't.

I understand that yoke V&H resistance should match, but what else makes tube compatible with a given chasis?
You really should measure inductance, not just resistance. Yoke specs have to match, as well as the neck connector and heater voltage. For the last two, there's Tubular.
 
Hmmm... My second monitor, which worked perfectly before, today also started behaving weird, this time horizontal overscan.

tn_Sanwa_3.jpg

Zoom in
 
anytime the picture on your monitor changes once they "warm up" it's a good indication that you have a faulty component somewhere, at that point its a good idea to start with a cap kit and then re-assess and troubleshoot once that's done.
 
OK, recap done!

tn_SanwaRep1.jpg

Zoom in

Helped with startup/warmup picture distortions.

tn_SanwaRep5.jpg

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Didn't help with picture not fitting into the screen.
Slightly not fitting at startup, and about 1.5cm over each margin after 20 minutes of beeing powered on.
Adjustment pots are set to the minimum width and height possible.

Any ideas where to look next?
 
I don't know much about this particular chassis but the next most likely culprit is the HOT (Horizontal Output Transistor)

Conventional wisdom is that the HOT is generally 100% working or 100% not working but I've seen them do some funny things just before failure. It could also be a flyback issue, but the HOT is way cheaper and easier to replace.

it also couldn't hurt to just physically inspect the adjustment pots and the width coil, make sure they aren't damaged and that the solder and traces around them look good. I've had quite a few adjustment pots fail on me (one of my MS8s needed 12 of them replaced). usually it's pretty obvious when they're dead because they wont respond to adjustment or they'll make huge jumps in output to only minor tweaks to their position.

A lot of times when I'm doing a cap kit I just retouch the solder on ANY joint that looks even remotely suspect... it wont hurt anything to put some fresh solder on there.
 
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Full kit should be 64 capacitors or 63, without C242, which is hard to get (470uF 160V high ripple).
Site says 60 + 2 optional, so I don't know what are 2 that missing and how critical they are.

I have ordered everything from local radio shop, it was 2 times cheaper than eBay (even not counting shipping).
For some caps they didn't have exact values and I used like 400v instead of 160v, but with same uF.
Well, also had to use 10uF+22uF soldered together instead of one bi-polar 33uF.

$27.50 is a good price, if you need to re-cap just 1 monitor.
If you have 3+, it may be would be better to buy bulk from the radio shop.
 
Talking of cap kits, is there a go to place you guys would recommend or do you just adhoc order caps?
If I'm re-capping a monitor I tend to just buy a kit that someone else has already put together. generally the price isn't much more than you'd pay buying a shipping caps piece-meal (in some cases it's even significantly less) and it will save you time hunting things down and will come with a nice printed cap list and in some cases the caps pre-organized.

if you're doing a lot of monitors, capping something where there is no good kit available, or simply want to have caps on hand then I use an electronics supplier like digkey. This will allow you to buy all or at least most of the parts you need from 1 shop, which will save on shipping and if you're buying in bulk you'll get really great prices too.
 
supplier like digkey.
Just be careful not to choose "USPS shipping - price unknown" option.
It means that they would rip you off.

I was expecting to get a calculation of shipping costs to my location,
instead I was just charged 67$ shipping for $27 parts order, which is like 150 grams and real shipping would be around $15.

Edit: Digikey refunded shipping costs as a sign of customer satisfaction importance.
Just wish it was more clear on the website, as here usually DHL/UPS is 4-5 times expensive than normal post.
 
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Well Digikey is a USA supplier, usually USPS delivery is the cheapest option (usually about $5 for me) inside the USA.

if you're not in the USA I would recommend finding an electronics supplier in, or closer to your country.
 
DHL was $30 on the same page.
Given that - could not expect they would just silently bill me $67 for USPS
DHL typically has the cheapest international shipping rates.

USPS "Priority" international service is extremely expensive, I could see it costings $67 given the price of other things I've shipped. Digikey doesn't up-charge their shipping services, you pay what they pay, and the price should be on the USPS label so you can confirm.

It sucks but maybe a lesson learned to not agree pay for things when the price is unknown ¯\_(ツ)_/¯
 
Yeah digikey has always been $$$$$ when shipping outside the US unfortunately.

So when people use the general term of 'service' the chassis are we basically referring to a recap and then progress from there if it is still faulty? or is there an actual process i.e things that should be measured etc
 
I don't think anyone who makes a living out of servicing these does a full recap for a faulty chassis. Doing one takes a ton of time, probably not worth it to the customer if you're charging by the hour.

I recapped two 29E31S chassis just recently, and I tested some of the caps with an ESR meter and they were fine. I only remember the two 330uf 35V caps being out of spec.

I bet guys like jomac and grantspain change only capacitors that they know can go bad unless asked otherwise. The AO wiki has a page on some common MS8 faults:

https://wiki.arcadeotaku.com/w/Nanao_MS8-29

"Change C911 C913 C442", not "do a full recap".
 
Yeah fair point Nem. Change bad caps, test unit and rinse repeat as required.
 
Today I have tried connecting external control panel from other Sanwa I have here.
And magick - with this panel I can adjust vertical size to fit the screen.

Investingation shows that Vertical Size pot on the second board is different version (looks different as well) and it is not full 1K Ohms, but 0.9K.
So for now I have added 2K bypass resistor on top of 2.2K, which is right after the pot (R315), and now it works.

Horizontal size is still too large to fit.

Dying flyback?
Faulty transistors?
(visual inspection does not show any cracks, burns, etc)
 
Actually, if your picture is not going out of focus, then it probably isn't the flyback.

Since you have two chassis, you could try swapping the HOT.
 
Given that a different remote board fixed the vertical issue, I wonder if the chassis was intended for a different model tube and either the tube or the chassis was throw in that cab just to get it "working" for sale.

Before you get too much further into this I would recommend writing down the Tube model number and measuring the resistance (and impedance if you can) of the yoke on BOTH of your machines.

just to make sure they're in-spec.
 
Tubes are the same (73SX701Y22-DC23), chassis boards are identical as well.
It is just the front panel pots, that are different. (Front pcbs are also identical, just different pot batch, it seems).

Unfortunatly it is not reasonable to swap something from the second monitor for testing, as it is not working as of now.
It was ok, when it arrived, than after a few days it started showing horizontally overlaped image.
I have recapped it half an hour ago - still same behaviour.
 
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