Help with Old InterTan (Tandy) Monitor

[roadrash]

Re: Help with Old InterTan (Tandy) Monitor

Ok sorry about that I wondered what happenend to the paper clip.
Aany idea what could have happened?

[R_J]

Re: Help with Old InterTan (Tandy) Monitor

I have no idea, did you check the voltages opn the secondary to see if they were correct after replacing the ic? Is that 1Ω ok or is it open? where is it in the circuit? was the ic running hot?
Since there is no schematic, Can you now provide a picture of the trace side of the board.

[roadrash]

Re: Help with Old InterTan (Tandy) Monitor

Can you point out where the 1Ω resistor your talking about, I can only see a 100Ω item? I didnt notice anything getting hot and there are no burning or dicolorations on the board anywhere. Here is a picture of section of the board where these parts were located in RED plus one of the whole PCB. Here too is a picture of the parts I removed to gain access and the 3 parts I replaced wuth New items. This was a mystery because there was no apparent reason for this and no clues it was about to happen.

[R_J]

Re: Help with Old InterTan (Tandy) Monitor

I thought I did point out the resistor, seems to go between pin 8 and ground. Also check that 47Ω ½w R007
Did you check the transistors in the bad stk to see which ones were shorted?

[roadrash]

Re: Help with Old InterTan (Tandy) Monitor

Yes you were right about the 1Ω resistor being open and the one close to it 100Ω is also open. Actually you can just make out a dark spot on it, which is from it going "POP".
Can you tell me what type & wattage those resistors are, also they are on extra posts I notice, do I need to reuse these for reinforcement or whatever they are for?
you asked me did I check the voltages opn the secondary to see if they were correct after replacing the ic. Please can you explain what voltages I am looking for and where. I dont understand "opn on the secondary" I'm sorry I am still learning all the terms..

[R_J]

Re: Help with Old InterTan (Tandy) Monitor

voltages opn the secondary = voltages on the secondary, just a typing error.
I believe the 100Ω is likely 1 watt flame proof, the 1Ω could be a 2 watt flame proof
You should be able to remove the standoffs, I would reuse them, it makes mounting the resistors easier as the holes are quite large for the resistor leads otherwise.
Did you check the other resistors in that circuit? I would also replace those two elec. caps,
As for the voltages, I don't know what they should be but just make sure they are not exceding the cap voltages, If the picture width and height were ok I suspect the voltages were close to what they should be.
If the voltage was too high I suspect the picture would also be stretched.

[roadrash]

Re: Help with Old InterTan (Tandy) Monitor

Both the resistors are the same physical size so I thought they were both 3 watt and have ordered them? I could only find metal film ones I'm afraid, will they still do?
Yes I did check all the resistors & diodes after that.
Ok will replace those 2 caps as well.
Was it a case of these components being weakened as I mentioned earlier, that caused this failure? Is it likely that these resistors blowing have damaged the STK Regulator and that Vert transistor again? I checked the rectifier and it was still ok.
I did notice something I didnt before and that was the STK73410II that I ordered came as a STK73410, I hope this is still compatabe? or I will have to get the seller to refund or send the right one.

[R_J]

Re: Help with Old InterTan (Tandy) Monitor

The vertical ic will be fine, I asked you before to check the stk transistors, I suspect the stk transistors shorted, blowing the resistors.
Maybe one of the resistors was open before, If you check the original stk, that might tell you if the transistor was shorted which resistor it my have damaged.

[roadrash]

Re: Help with Old InterTan (Tandy) Monitor

You are reffering to the internal transistors in the STK I gather? That was a brand new component I put in there so it couldn't be that which blew the resistors surely? I will test the STK's diodes and transisors as best I can and as shown on the data sheet and if they are suspect I will order another I wil order another one.

The vertical ic will be fine, I asked you before to check the stk transistors, I suspect the stk transistors shorted, blowing the resistors.
Maybe one of the resistors was open before, If you check the original stk, that might tell you if the transistor was shorted which resistor it my have damaged.

[R_J]

Re: Help with Old InterTan (Tandy) Monitor

The ORIGINAL stk shorted, correct? so when IT shorted it likely opened or increased the value of one of the resistors, when you replaced the stk with the new one, the resistor being open may have caused the transistor to be poorly biased and may have caused the stk transistor to short again.
If the original stk's output transistor was shorted, it would have damaged the 1Ω resistor. 160 volts on the collector, it shorts to the emitter applying 160v across 1Ω. If that happened the resistor may have increased to 10Ω or more. the ic worked for a short time then the transistor likely shorted again.

[roadrash]

Re: Help with Old InterTan (Tandy) Monitor

I thought that 1Ω resistor went "pop" after I replaced all the IC's reg & Rect and after I had it working again for the 1st time. I have no idea if the original STK73410II was blown after the original short as I just replaced everything with new items (The STK, Rect & Vert transistor) but I never checked the resistors at that time although I did check all diodes. Maybe thats where I slipped up as not only was the 1Ω resistor blown with a hole but the 100Ω 3w one near it is also testing as faulty so maybe it was a faulty 100Ω one that caused the 1Ω to go pop too.
Anyway ive now replaced The STK again along with those 2 resistors and all the 1uf & 10uf caps there too. The rectifier I tested and is still ok so ive left it and the vertical transistor you say will still be ok too.
I am just waiting on a proper "STK73410II" coming any day. As I mentioned the one I was sent from ebay was a STK73410 with no other markings or brand name so I dont know if it was 100% compatable now and cant find anything online about what the difference was between the 3 versions of this chip were. This too may have been a cause of the failure. Anyway I will know very soon now when I get that New "STK73410II" soldered in. I might need advice on checking these voltages you mentioned when I get it working gain.

The ORIGINAL stk shorted, correct? so when IT shorted it likely opened or increased the value of one of the resistors, when you replaced the stk with the new one, the resistor being open may have caused the transistor to be poorly biased and may have caused the stk transistor to short again.
If the original stk's output transistor was shorted, it would have damaged the 1Ω resistor. 160 volts on the collector, it shorts to the emitter applying 160v across 1Ω. If that happened the resistor may have increased to 10Ω or more. the ic worked for a short time then the transistor likely shorted again.

[roadrash]

Re: Help with Old InterTan (Tandy) Monitor

A result at last. This time its been running for hours no problem. That will teach me to check all the resistors as well as the diodes. Thanks RJ. Here's a picture of the old vintage Tandy (Intertan) working again with its maching monitor.
Its running the first version of windows.