Recent content by Hugo Holden

One interesting thing I found with the corrosive nature of leaked electrolyte, initially at least after it leaks, is pH is fairly close to neutral, it has very low electrical conductivity. But, after it has come into contact with solder and pcb tracks for a while, it undergoes an alkaline shift...

suddenly: the monitor lost control of its brightness, and the horizontal & vertical sizes went out of whack, There is no CRT (tube) fault that will cause this. It is an electronic fault, your CRT itself will likely be fine. If the H + V scan sizes went "out of whack" proportionally that...

If I were you I would buy a GQ-4x programmer that can support the 2532's and a number of other vintage computer chips you will come across if you are interested in vintage computers, they are reliable, work well, are in a proper housing , not a bare pcb waiting to be shorted out on the desk, and...

Do you ever get the feeling you have seen something before, but cannot remember exactly where ? When I saw the PET's 4 state machine I had a feeling I had seen the circuit configuration before with the JK flip flops. Looking at it again recently I noticed that its two outputs resulted in a 90...

Likely you do have ROM issues, since you have excluded most of the other common issues. There are different approaches, one is to look a the ROM checksums, or read them (you can set the programmer to TMS2532 to read them) compare their files to the ones at Zimmers. With these original ROM's...

One problem driving cables is that they have distributed capacitance and inductance per unit length. This sets up the conditions for oscillations or ringing and that can corrupt data. The lower the resistance value in the LCR combination, the more likely oscillations occur. And with longer...

Great simulations. Anything that can help create a database of how the PETs operate will assist repairs. I was also very interested in the early non CRTC PETs and the generation of video from TTL devices. One reason is that I had worked extensively with early video games from the 1970's such as...

Line driver IC's that interface between different pieces of equipment are highly vulnerable to damage. Not just from cable shorts, wrong connectors or peripherals grounding or applying voltage to pins, but other issues even when all is normal. Any peripheral apparatus that does not have its...

In some of these VDU's the original 7812 was held down by a rivet. That distorted the tab around the hole and then it relied much more on the thermal paste and it then gave trouble later when it dries out. Thermal paste is not the most wonderfully thermally conductive substance, despite the...

It sounds very much like the regulator is going into over-temperature thermal shut down mode. In this VDU they pushed the 7812 to ts limits thermally, in that its dissipation is high. It relies on adequate heat sinking, meaning it has to be screwed down firmly to the heat sink with fresh heat...

Good thing it wasn't a cmos chip, they can often work most of the time with the power pin not connected because they can source power by inputs and the substrate diodes, until, some logic condition occurs where all the input pins are low at the same time and the circuit malfunctions.

No it is not the voltage multiplier capacitance that determines what current you would get in the de-powered state, it is the reverse leakage of the final diodes in the chain. I am not sure where you are getting these ideas. All of the capacitors in the multiplier have a voltage rating that...

Sorry to disagree, it is not dangerous at all to disconnect the external dag on a CRT (with the set de-powered) regardless if it a multiplier, or simple rectifier at all and if the CRT bulb is charged. There is an insufficiently low resistive pathway via the multiplier's rectifiers to receive...

The same thing I said applies to voltage multipliers or single diode EHT, the reverse leakage current is far too low to sustain any significant current via the external dag and ground, if it was a leakage current of any significance the bulb capacitance would have already been discharged after...

If you click on that "Pardon our Interruption" remark, it goes to the page I linked. Can anyone explain what that message means and why it comes about ? It reminds me of a remark on Star Trek when Spock said to Nero: "Pardon me, I do not believe we are acquainted"