Help with Old InterTan (Tandy) Monitor

[roadrash]

Something unfortunate happened recently when I was looking into my InterTan monitor after the On/Off switch stopped latching. I was going to put a cable tie round it to keep in turned on at the switch perminantly and just turn it on & off at the wall. But I dropped the end out of my screwdriver into the open monitor when it was turned on. It fell down by the on/off switch and I would guess it must have shorted the Live & Neutral wires that are right beside it. It did pop the fuse but it just pops a new fuse if I put one in so somethingelse is blown as well.
Not sure what make this monitor is but I bet its not Tandy made. Anyway I have uploaded a whole lot of photos of it here for you to see.
https://drive.google.com/open?id=1ZA...OHIe7UWmJDOvmS

I have it stripped on my bench and so far all diodes I have checked including the one right near the Switch are OK.

https://drive.google.com/file/d/17M5...ew?usp=sharing

I would really appreciate if someone please help me track down what it is I have popped as I really need this monitor and I feel so stupid now for leaving it opened up while it was turned on.

[R_J]

Re: Help with Old InterTan (Tandy) Monitor

Any model or chassis number on the back? Its a good chance the regulator ic is bad, (looking from the back, the ic is mounted to the aluminum heatsink), could be a str???? Also check the horz. output transistor if its not shorted I would go after the regulator or the bridge rectifier

[roadrash]

Re: Help with Old InterTan (Tandy) Monitor

Thanks RJ for the help, you have helped me a few times now in the past and I am very grateful.
The main PCB has the following numbers:

9979800219-07
1V0-0
201KY15661

On the back of the monitor cabinet is has the following info:

Model VCM-100
25-9090A
2A2
February 1992
Made in Korea.

Those heatsinks are large, just hope my soldering iron will be able to get hot enough to desolder them from the PCB. Unfortunately it looks like at least one of them will need removing to allow access to the components.

[R_J]

Re: Help with Old InterTan (Tandy) Monitor

If you can take a couple pictures on the bottom of the board, and post them here that would help, that way some checks could be done, maybe the heat sinks don't need to be removed, if they do it is likely there are small pins that are connected and go through the baord.

[roadrash]

Re: Help with Old InterTan (Tandy) Monitor

Got the heatsinks off, it wasn't that bad actually. The rectifier is a LB56 & the Regualor like you saaid is a STR73410.II.
Ive got the data sheet with Schematic for the STR so I think I can work out how to test it. Am I right in saying I check all the diodes that are in circuit between pins. Sorry for being dumb but where is the "horz. output transistor" ?

[R_J]

Re: Help with Old InterTan (Tandy) Monitor

The horz. output is likely ok since the screwdriver was droped in the switch area (its the transistor mounted to the heatsing that wraps around the flyback transformer)
I would check the bridge rectifier first, it is just 4 diodes in one case.
That is STR74310 and not STK74310 correct?

[roadrash]

Re: Help with Old InterTan (Tandy) Monitor

The LB156 10A is OK. I thought it was open circuit until I realised the "Hold" button was pressed. So it must be the Regulator is there a particular way I test the Regulator? Is that other transistor you mention on the heatsink a AN5515 integrated circuit?

[R_J]

Re: Help with Old InterTan (Tandy) Monitor

The AN5515 is the vertical output ic, The horizontal output is on the heatsink that is next to the highvoltage transformer (flyback)
I could'nt find much information on the STR73410.II But it seems to be a smps ic not just a simple regulator ic

[petehall347]

Re: Help with Old InterTan (Tandy) Monitor

bringing back memories of old tv.s .. H.O.T first port of call with most of them .

[roadrash]

Re: Help with Old InterTan (Tandy) Monitor

Ive found replacement STR73410 and AN5515 and they are not expensive so I will get some and replace them now its stripped. What are the chances the HOR transisor could be gone as well because I found one of these to and also cheap. Please elaborate on H.O.T.???

[petehall347]

Re: Help with Old InterTan (Tandy) Monitor

horizontal output transistor

[roadrash]

Re: Help with Old InterTan (Tandy) Monitor

Thanks when the new parts arrive I will reassemble it and let you know if it works again
(I really hope so).. Thanks

[sean0118]

Re: Help with Old InterTan (Tandy) Monitor

I wouldn't replace the horizontal output transistor, unless you test it out of circuit and find it's shorted. You know the one in there now is legitimate, while one you buy may be counterfeit and create more problems.

With it unplugged from the wall, have you tried measuring the resistance from the secondary side of the fuse to neutral?

[roadrash]

Re: Help with Old InterTan (Tandy) Monitor

the new STR73410 regulator arrived today along with the AN5515 HOR transistor. What a job soldering in that new regulator. There was a transformer and Large capacitor in the way and I could not get the legs to line up with the holes and if I put it in before fitting the heatsink that transformer and capacitor were in the way of the screws. Anyway I removed those bits and fitted the regulator and HOR transistor. All went well except 2 pads on the regulator lifted from the board but when I check them they do not seem to join to any track so maybe they are not used. The pins were 3 & 4 and I notice pin 6 also has no track to it.
Can someone please check that this makes sense, Here is a link to the datasheet for the STR73410 which has a schematic. https://drive.google.com/open?id=1ZO...2p21pa56b-GtcV

[R_J]

Re: Help with Old InterTan (Tandy) Monitor

The AN5515 is the VERTICAL OUTPUT IC, Not the HOR transistor. It looks like those pins (3 & 4) are not be used.
If you look at the internal schematic of the stk ic you should be able to check the tr3 and tr2 transistors to see if they were shorted

[roadrash]

Re: Help with Old InterTan (Tandy) Monitor

Thanks for correcting me there RJ. Could you please answer me a question ive wondere for a long time regarding electronic components. Using this short as an example,
can components be weakeed by a event such as a short? Sorry thinking as mechanic (like I am) If this is the case it would make sense to repace such componenets to save them possibly failing prematurly in the future. Or are components just either good or bad and cannot be weakened.

[R_J]

Re: Help with Old InterTan (Tandy) Monitor

I would say the other parts would be fine, the fuse blew so nothing else should have a problem, ie: the bridge and main cap. would be fine, maybe if you replaced the fuse with a 1/4" bolt it might have damaged the bridge but everything else should be ok. If a part is weak it will likely fail within a short time of operation, thats why we usually run a product for a while after a repair.
I still don't know what parts are damaged, but a short in the secondary somewhere or around the ic would have likely caused the switching transistor in the ic to exceed its current capability and short out. that blew the fuse like it should.

[roadrash]

Re: Help with Old InterTan (Tandy) Monitor

Thank you for clarifying that for me. So parts can be weakened. I'm Glad I replaced all three of the parts that could have been damaged no.

Anyway, the good news is that the last parts (rectifier) arrived today and it works!.
Many thanks to everyone once again, you are stars!
Cheers!!

I would say the other parts would be fine, the fuse blew so nothing else should have a problem, ie: the bridge and main cap. would be fine, maybe if you replaced the fuse with a 1/4" bolt it might have damaged the bridge but everything else should be ok. If a part is weak it will likely fail within a short time of operation, thats why we usually run a product for a while after a repair.
I still don't know what parts are damaged, but a short in the secondary somewhere or around the ic would have likely caused the switching transistor in the ic to exceed its current capability and short out. that blew the fuse like it should.

[roadrash]

Re: Help with Old InterTan (Tandy) Monitor

Well that didnt last long. After all that I hooked it up to the old Tandy computer it goes with and It seemed to be completely fine with a good dispaly. The as I was standing there watching it boot up I heard a dull sounding "POP" and it went dead again. There was no smell or any smoke just the POP.
Today I looked at and could see nothing external and the fuse was OK, so I undone everything I did to it ,removing all components & heatsinks again and inspecting them all for visible damage but can see nothing wrong with any of them. I tested the LB156 bridge Rectifier and it checks out as OK. Here are a few pictures of the PCB with the components and items in the way removed like a large capacitor and a transformer otherwise its just the rectifier, regulator, vertical transistor and heatsinks that are removed. Can someone tell me what the black box in one of the pictures is and how i test it (PR01).

Pictures here

Well now I am stumped. What could have caused the pop and it going dead?? any ideas anyone.

[R_J]

Re: Help with Old InterTan (Tandy) Monitor

If you post the pictures in the thread. Use the Go Advanced and click on the paper clip to attach them.
Pr01 is the degausing thermistor, it is a ptc, likely around 10 ohms cold, It is only used for degausing the crt, it won't effect the operation of the power supply
Check the 1Ω resistor