Wang 700b help

[jk31454]

We got a Wang 700 series calculator a while ago, and we tried to fix it. We are at a standstill and need help. The 5v (I think) regulator is broken, and one of the display cards is also. There may be more issues that we are not aware of. If anyone needs more info, I can take more pictures for them. Also, with a power supply hooked up, I do believe we weren't having display issues.

Here is a video without the variable power supply hooked up.

 

[BlaBla1985]

Heey, welcome to the forum!

I'm going to shamelessly plug the thread on my 700B. There is a link to the schematics on page 2 (in case you need those). Thread on my 700B

Hoping @durgadas311 sees this thread too, he was a big help when I was working on mine.

 

[durgadas311]

Lots of things will cause a blank display, since the display must be refreshed constantly in order for anything to appear. Basically, anything that prevents the microcode from running. Unfortunately, the microcode ROM in the 700s is of the wire-weave technology, which can be particularly fragile. I've been working with Andrew to get his 600 and 700s going. His 600 required a great deal of work, and a lot of custom microcode got written to help test bits of hardware. His 700s came up easier. However, in all cases he was not able to use the wire-weave ROMs. He's done a great job of documenting his progress, and he designed some hardware to dump the wire-weave ROMs (partially successful) and also to replace the wire-weave ROM with modern EPROM/EEPROM. Start with the documentation here: https://dopecc.net/latest/

You'll need to good logic analyzer, or at least a very capable multi-channel oscilloscope. Then it's a matter of tracing through and verify critical signals. You probably want to start collecting what's needed to build Andrew's "ROM Emulator" because you will need to assume that part of your problem is the wire-weave ROM not working 100%.

 

[jk31454]

Lots of things will cause a blank display, since the display must be refreshed constantly in order for anything to appear. Basically, anything that prevents the microcode from running. Unfortunately, the microcode ROM in the 700s is of the wire-weave technology, which can be particularly fragile. I've been working with Andrew to get his 600 and 700s going. His 600 required a great deal of work, and a lot of custom microcode got written to help test bits of hardware. His 700s came up easier. However, in all cases he was not able to use the wire-weave ROMs. He's done a great job of documenting his progress, and he designed some hardware to dump the wire-weave ROMs (partially successful) and also to replace the wire-weave ROM with modern EPROM/EEPROM. Start with the documentation here: https://dopecc.net/latest/

You'll need to good logic analyzer, or at least a very capable multi-channel oscilloscope. Then it's a matter of tracing through and verify critical signals. You probably want to start collecting what's needed to build Andrew's "ROM Emulator" because you will need to assume that part of your problem is the wire-weave ROM not working 100%.

Currently, the issue with the display is the lack of current going to the logic circuits. After I am able to fix that, I will replace the ROM if that's the issue.

 

[oldsarah]

Have you checked all the power supply voltages coming into the display board? Sometimes, a filtering cap needs replacing.

 

[jk31454]

Have you checked all the power supply voltages coming into the display board? Sometimes, a filtering cap needs replacing.

We checked the caps, they are all good. So is the 5v coming into the board (I think at least)

 

[oldsarah]

I see. Maybe the regulator is the problem.

 

[durgadas311]

I'm not exactly sure what your current problem is, but I assume you've got the schematics downloaded?

Keep in mind there are key components that use voltages other than 5V, so you'll want to examine the power supply schematics and other notes and verify that all voltages are present and within range. There are also higher voltages involved in lighting the nixie tubes, so use caution. It might even be prudent to get the power all working with no logic boards installed (as others have done during initial testing), and possibly even try to simulate a load on various voltages to confirm the power supply is functional. There are some delicate and fragile boards, particularly the core memory. As Andrew experienced with his Wang 600, some of these old ICs are susceptible to trauma and subsequent failure - and are not always easy to find replacements for. Given the number of blown chips on Andrew's 600, it certainly went through something traumatic before he acquired it.