A question from the unwashed relative to: I built a TM500 mainframe tester, and updated the design. Someone might find this useful?

#175733

TM500 - Ok, it fits a very large set of modules.  Why?  Are there modules that do things that can only be done using a particular module?  Yes, I could read the specs for dozens and dozens of the modules, but that would confuse my unwashed brain even further.  Is this admirable project useful in a way that my R&S RTB2000 and my Tek2465b would find it useful?

I do not want to in any way diminish the project.  I looks to be a true work of art and engineering.  But I have no 'modules' and certainly no power supply for same.  My oldest scope is my pride and joy: 2465BDM.  Why would I accumulate these modules?

I hope no-one hammers me into the ground.  I'm simply TOTALLY IGNORANT of these modules and the power supply for same.

Thank you,            larry

#175736

Ok, perhaps I can clear up a bit of this.

Remember that in the 70's to 90's (roughly) there were no (to speak of) FPGA IC's so digital design was lots of 14, 16, 20, and maybe 40 pin chips, depending on the design.? The more (and perhaps most) complicated chips were 8 bit microprocessors, 64K address space, etc.? If you don't know exactly how this maps out, consider that the processor in your smart phone is a genius, and the processors of that time were, if at all, clever chimpanzees (with apologies to Ham and Bonzo).

So we have designs with a lot of chips, lots of discrete parts, and so on.? Tektronix was doing well in oscilloscopes, but had no share (much) in the test equipment market.? You'd need pulse generators, sine wave generators, function generators, meters, power supplies, and others.

So Tektronix looked at the market for test equipment, and likely noticed several things:? 1) a lot of test equipment setups needed a function generator, meters, power supplies and other goodies. 2) they weren't making any of them, 3) these things were expensive and they were fairly large in size.? 4) a small size test setup, rack mount, desk top, or even portable (look up TM515), well, that could be useful., and 5) if they could figure out a way to sell bits 'n' pieces, and allow people to just buy what they needed, well, maybe there's a market there.

Enter the TM500 series.? Very few have microprocessors, having been designed before the widespread use of such (now, if it DOESN'T have one, it's worthy of note).

Most are discrete circuitry, some have ICs, some have some complex digital circuitry (a counter is not absolutely a simple design..... especially period and time measurements).

So what Tek did is to design a standard sized frame (same width as the 7000 series), same height as the 7000 series, but more shallow.? (saved manufacturing costs).? They provided three DC supplies, a + 11, a +35 and a -35.? Once regulated down, each bulk supply could be used for a number of projects.? They also supplied, *per plugin slot*, three AC windings which could be connected and used to make isolated power supplies in each module (and you need this for meters, for instance).? The DC supplies were all pretty much referenced to a common ground.? In addition, the connector (per module) had a LOT of unused pins.? Those pins could connect to individual circuits in the module, and would allow the backplane to be wired in such a way that the front panel connections would be duplicated on the backplane.? This would allow dedicating slots to a particular configuration, and minimizing front panel connections.? An example would be wiring the output of a power supply to a DMM, or? wiring the output of a frequency source to a counter.? All done under the table.

For power supplies, there are 1,2,3,4,5 and 6? slot frames.? The 5 slot frame is in a luggage style sealed enclosure, and was designed to be able to be shipped on an aircraft, so you could take your test equipment with you.? Tektronix also had oscilloscope modules ranging from small, low bandwidth modules, to storage, to 80 Mhz dual channel scope plugins (double width).

Modules evolved in capability as time went on, so you have 3.5 digit DMMS without autoranging, 3.5 digit DMMs with autoranging, simplified lower cost DMMS, and the like.? Pulse generators went from general purpose to 250 Mhz generators to a specialized 70+ volt output generator with variable rise times.? Function generators were sine, square wave, triangle wave, ramp, pulse, etc.... All depended on which one.? Some had built in frequency modulators and could do (to an extent) pulse trains.

There were power supplies, single, dual, and triple outputs, oscilloscope modules, function generators, pulse generators, meters, frequency counters, digital delays, logic analyzers, and so on (check the TEKWIKI for a good idea, or look in the catalogs).

One problem (at least one) was the development of ATE (hereinafter known as Automatic Test Equipment), in other words, run by a computer.? Tek brought out the TM5000 series, with a slightly different design, but including two very specific extras, a microprocessor controlling everything, and an IEE-488 (GPIB/HPIB) interface.? This allowed the test equipment to make measurements, set up conditions, and such under computer control. They had computer controlled switches and digital input/output modules.

Other modules would include such specialized things as optical (fiber optics) measurements, and the like (don't have any of them!)

So in short:? A modular equipment system consisting of a rack, and plugin modules designed to be used in test equipment setups, very capable of being customized.? Need a rack with 5 DMMS?? go for it.? Rack with 3 counters and 3 signal generators?? Easy. Next setup?? unplug the modules, put them back in stock, get the new modules out, plug them in, and you've reconfigured the whole thing.

WIthin the limits of the equipment and the technology of the time, it was a very good idea.

Harvey

Show quoted text

On 1/1/2021 6:52 PM, Lawrance A. Schneider wrote:
TM500 - Ok, it fits a very large set of modules.  Why?  Are there modules that do things that can only be done using a particular module?  Yes, I could read the specs for dozens and dozens of the modules, but that would confuse my unwashed brain even further.  Is this admirable project useful in a way that my R&S RTB2000 and my Tek2465b would find it useful?

I do not want to in any way diminish the project.  I looks to be a true work of art and engineering.  But I have no 'modules' and certainly no power supply for same.  My oldest scope is my pride and joy: 2465BDM.  Why would I accumulate these modules?

I hope no-one hammers me into the ground.  I'm simply TOTALLY IGNORANT of these modules and the power supply for same.

Thank you,            larry

#175737

Thank you very much, Harvey, for that great historical summary!

— Happy New Year
Tom

Sent from my iThing, so please forgive typos and brevity.

Show quoted text

On Jan 1, 2021, at 5:10 PM, Harvey White <madyn@...> wrote:

?Ok, perhaps I can clear up a bit of this.

Remember that in the 70's to 90's (roughly) there were no (to speak of) FPGA IC's so digital design was lots of 14, 16, 20, and maybe 40 pin chips, depending on the design.  The more (and perhaps most) complicated chips were 8 bit microprocessors, 64K address space, etc.  If you don't know exactly how this maps out, consider that the processor in your smart phone is a genius, and the processors of that time were, if at all, clever chimpanzees (with apologies to Ham and Bonzo).

So we have designs with a lot of chips, lots of discrete parts, and so on.  Tektronix was doing well in oscilloscopes, but had no share (much) in the test equipment market.  You'd need pulse generators, sine wave generators, function generators, meters, power supplies, and others.

So Tektronix looked at the market for test equipment, and likely noticed several things:  1) a lot of test equipment setups needed a function generator, meters, power supplies and other goodies. 2) they weren't making any of them, 3) these things were expensive and they were fairly large in size.  4) a small size test setup, rack mount, desk top, or even portable (look up TM515), well, that could be useful., and 5) if they could figure out a way to sell bits 'n' pieces, and allow people to just buy what they needed, well, maybe there's a market there.

Enter the TM500 series.  Very few have microprocessors, having been designed before the widespread use of such (now, if it DOESN'T have one, it's worthy of note).

Most are discrete circuitry, some have ICs, some have some complex digital circuitry (a counter is not absolutely a simple design..... especially period and time measurements).

So what Tek did is to design a standard sized frame (same width as the 7000 series), same height as the 7000 series, but more shallow.  (saved manufacturing costs).  They provided three DC supplies, a + 11, a +35 and a -35.  Once regulated down, each bulk supply could be used for a number of projects.  They also supplied, *per plugin slot*, three AC windings which could be connected and used to make isolated power supplies in each module (and you need this for meters, for instance).  The DC supplies were all pretty much referenced to a common ground.  In addition, the connector (per module) had a LOT of unused pins.  Those pins could connect to individual circuits in the module, and would allow the backplane to be wired in such a way that the front panel connections would be duplicated on the backplane.  This would allow dedicating slots to a particular configuration, and minimizing front panel connections.  An example would be wiring the output of a power supply to a DMM, or  wiring the output of a frequency source to a counter.  All done under the table.

For power supplies, there are 1,2,3,4,5 and 6  slot frames.  The 5 slot frame is in a luggage style sealed enclosure, and was designed to be able to be shipped on an aircraft, so you could take your test equipment with you.  Tektronix also had oscilloscope modules ranging from small, low bandwidth modules, to storage, to 80 Mhz dual channel scope plugins (double width).

Modules evolved in capability as time went on, so you have 3.5 digit DMMS without autoranging, 3.5 digit DMMs with autoranging, simplified lower cost DMMS, and the like.  Pulse generators went from general purpose to 250 Mhz generators to a specialized 70+ volt output generator with variable rise times.  Function generators were sine, square wave, triangle wave, ramp, pulse, etc.... All depended on which one.  Some had built in frequency modulators and could do (to an extent) pulse trains.

There were power supplies, single, dual, and triple outputs, oscilloscope modules, function generators, pulse generators, meters, frequency counters, digital delays, logic analyzers, and so on (check the TEKWIKI for a good idea, or look in the catalogs).

One problem (at least one) was the development of ATE (hereinafter known as Automatic Test Equipment), in other words, run by a computer.  Tek brought out the TM5000 series, with a slightly different design, but including two very specific extras, a microprocessor controlling everything, and an IEE-488 (GPIB/HPIB) interface.  This allowed the test equipment to make measurements, set up conditions, and such under computer control. They had computer controlled switches and digital input/output modules.

Other modules would include such specialized things as optical (fiber optics) measurements, and the like (don't have any of them!)

So in short:  A modular equipment system consisting of a rack, and plugin modules designed to be used in test equipment setups, very capable of being customized.  Need a rack with 5 DMMS?  go for it.  Rack with 3 counters and 3 signal generators?  Easy. Next setup?  unplug the modules, put them back in stock, get the new modules out, plug them in, and you've reconfigured the whole thing.

WIthin the limits of the equipment and the technology of the time, it was a very good idea.

Harvey

On 1/1/2021 6:52 PM, Lawrance A. Schneider wrote:
TM500 - Ok, it fits a very large set of modules.  Why?  Are there modules that do things that can only be done using a particular module?  Yes, I could read the specs for dozens and dozens of the modules, but that would confuse my unwashed brain even further.  Is this admirable project useful in a way that my R&S RTB2000 and my Tek2465b would find it useful?

I do not want to in any way diminish the project.  I looks to be a true work of art and engineering.  But I have no 'modules' and certainly no power supply for same.  My oldest scope is my pride and joy: 2465BDM.  Why would I accumulate these modules?

I hope no-one hammers me into the ground.  I'm simply TOTALLY IGNORANT of these modules and the power supply for same.

Thank you,            larry

#175740

I should mention one other thing.? To make the inboard power supplies more possible, and to remove heat from the module, TEK put in a general purpose PNP power transistor and a general purpose NPN power transistor in the frame.? They put in one per slot.? The general idea was to use them for the pass transistors for an on-board regulated positive supply, and an on board regulated negative supply.? The regulator controllers were on the board, the pass transistors were on a nice metal frame that got rid of a lot of heat easily.? These need to be tested.? Your average module tester needs to make sure that the AC windings are properly phased and connected, the DC supplies are within spec (they're all bulk supplies with the exception of the TM5000 low voltage supply: regulated).? The last item is to make sure that the pass transistors are isolated from the frame, and are operational.? Plugins needing more 5 volts or so than could be well built may have a switching supply from 11.5 volts.? Other supplies needed may have 3 terminal regulators or not, but a power supply design for any module generally had to do something.? 11.5 volts unregulated with a 3 volt minimum drop across a 7805 drops down to 8.5 volts, and the regulator is good for an amp or so, so about 7.5 watts/amp drawn, and the case could be the heatsink IF the NPN transistor were not used.

Harvey

Show quoted text

On 1/1/2021 8:09 PM, Harvey White wrote:
Ok, perhaps I can clear up a bit of this.

Remember that in the 70's to 90's (roughly) there were no (to speak of) FPGA IC's so digital design was lots of 14, 16, 20, and maybe 40 pin chips, depending on the design.? The more (and perhaps most) complicated chips were 8 bit microprocessors, 64K address space, etc.? If you don't know exactly how this maps out, consider that the processor in your smart phone is a genius, and the processors of that time were, if at all, clever chimpanzees (with apologies to Ham and Bonzo).

So we have designs with a lot of chips, lots of discrete parts, and so on.? Tektronix was doing well in oscilloscopes, but had no share (much) in the test equipment market.? You'd need pulse generators, sine wave generators, function generators, meters, power supplies, and others.

So Tektronix looked at the market for test equipment, and likely noticed several things:? 1) a lot of test equipment setups needed a function generator, meters, power supplies and other goodies. 2) they weren't making any of them, 3) these things were expensive and they were fairly large in size.? 4) a small size test setup, rack mount, desk top, or even portable (look up TM515), well, that could be useful., and 5) if they could figure out a way to sell bits 'n' pieces, and allow people to just buy what they needed, well, maybe there's a market there.

Enter the TM500 series.? Very few have microprocessors, having been designed before the widespread use of such (now, if it DOESN'T have one, it's worthy of note).

Most are discrete circuitry, some have ICs, some have some complex digital circuitry (a counter is not absolutely a simple design..... especially period and time measurements).

So what Tek did is to design a standard sized frame (same width as the 7000 series), same height as the 7000 series, but more shallow.? (saved manufacturing costs).? They provided three DC supplies, a + 11, a +35 and a -35.? Once regulated down, each bulk supply could be used for a number of projects.? They also supplied, *per plugin slot*, three AC windings which could be connected and used to make isolated power supplies in each module (and you need this for meters, for instance).? The DC supplies were all pretty much referenced to a common ground.? In addition, the connector (per module) had a LOT of unused pins.? Those pins could connect to individual circuits in the module, and would allow the backplane to be wired in such a way that the front panel connections would be duplicated on the backplane.? This would allow dedicating slots to a particular configuration, and minimizing front panel connections.? An example would be wiring the output of a power supply to a DMM, or? wiring the output of a frequency source to a counter.? All done under the table.

For power supplies, there are 1,2,3,4,5 and 6? slot frames.? The 5 slot frame is in a luggage style sealed enclosure, and was designed to be able to be shipped on an aircraft, so you could take your test equipment with you.? Tektronix also had oscilloscope modules ranging from small, low bandwidth modules, to storage, to 80 Mhz dual channel scope plugins (double width).

Modules evolved in capability as time went on, so you have 3.5 digit DMMS without autoranging, 3.5 digit DMMs with autoranging, simplified lower cost DMMS, and the like.? Pulse generators went from general purpose to 250 Mhz generators to a specialized 70+ volt output generator with variable rise times.? Function generators were sine, square wave, triangle wave, ramp, pulse, etc.... All depended on which one.? Some had built in frequency modulators and could do (to an extent) pulse trains.

There were power supplies, single, dual, and triple outputs, oscilloscope modules, function generators, pulse generators, meters, frequency counters, digital delays, logic analyzers, and so on (check the TEKWIKI for a good idea, or look in the catalogs).

One problem (at least one) was the development of ATE (hereinafter known as Automatic Test Equipment), in other words, run by a computer.? Tek brought out the TM5000 series, with a slightly different design, but including two very specific extras, a microprocessor controlling everything, and an IEE-488 (GPIB/HPIB) interface.? This allowed the test equipment to make measurements, set up conditions, and such under computer control. They had computer controlled switches and digital input/output modules.

Other modules would include such specialized things as optical (fiber optics) measurements, and the like (don't have any of them!)

So in short:? A modular equipment system consisting of a rack, and plugin modules designed to be used in test equipment setups, very capable of being customized.? Need a rack with 5 DMMS?? go for it.? Rack with 3 counters and 3 signal generators?? Easy. Next setup?? unplug the modules, put them back in stock, get the new modules out, plug them in, and you've reconfigured the whole thing.

WIthin the limits of the equipment and the technology of the time, it was a very good idea.

Harvey

On 1/1/2021 6:52 PM, Lawrance A. Schneider wrote:
TM500 - Ok, it fits a very large set of modules.? Why?? Are there modules that do things that can only be done using a particular module?? Yes, I could read the specs for dozens and dozens of the modules, but that would confuse my unwashed brain even further.? Is this admirable project useful in a way that my R&S RTB2000 and my Tek2465b would find it useful?

I do not want to in any way diminish the project.? I looks to be a true work of art and engineering.? But I have no 'modules' and certainly no power supply for same.? My oldest scope is my pride and joy: 2465BDM.? Why would I accumulate these modules?

I hope no-one hammers me into the ground.? I'm simply TOTALLY IGNORANT of these modules and the power supply for same.

Thank you,??????????? larry

#175741

On Fri, Jan  1, 2021 at 03:52 PM, Lawrance A. Schneider wrote:

Ok, it fits a very large set of modules. Why? Are there modules that do things
that can only be done using a particular module?
My perspective being an electronics, amateur radio and RF engineering born again newbie with more from a chemist, with a chemometrics, programming, lab qualification/validations and leadership perspective was to lead on my calibrations equipment development so I'd have a way to utilize the CG5001 as well as have a more analog system for whatever came next, like the 7904. 

I wound up investing in a TM5006 which came with the DMM and power supply modules.  I've since invested in the Function Generator. 

Harvey couldn't of said any better.   

I also have a goal to make a module, though most likely for the 7904 that's a NIR-Vis-UV spectrophotometer.  I do have a PMI 1038 with a range of SNA modules... that inspired (or corrupted me) to set a goal to make microwave related spectrum analysis modules also.  So technically, I do have the D14 where I can possibly have a go at a 5000 serial module also.

Reminds me to look into an excuse for investing in a HP9836 not only for, the NS20/NS201's, a Tektronix application.  Hhhmmm, maybe a custom module?

Now, the TM500/5000 series mainframe tester is on my mind as a "must have at some time" and will fit in to the project plans as convoluted as they can.

Why would I accumulate these modules?I'm not a mind reader... for whatever you find useful or enjoyable or as a goal in this life.

#175747

On Fri, Jan  1, 2021 at 06:08 PM, Harvey White wrote:


... needs to make sure that the AC windings [on the frame] are
properly phased and connected...
But why? (Surely, frames didn't leave the factory, with miswired phasing [it's been mentioned plug-in were non-disposable back in the day!] )
And as to all the gremlins, re-arranging the wiring, before the frame hits the GoodWill... is that a thing?
Hands up if that's happened to you.

#175749

On Fri, Jan  1, 2021 at 06:08 PM, Harvey White wrote:


..the pass transistors were on a nice metal frame that got rid of a lot of heat
easily.? These need to be tested.
Yes... but, do they have to be "tested" by incorporating a "fuse tester" in the tester. Seems inelegant to me.

#175751

On Fri, Jan  1, 2021 at 03:52 PM, Lawrance A. Schneider wrote:


Is this admirable project useful in a way that my R&S RTB2000 and my Tek2465b
would find it useful?
....
Why would I accumulate these modules?
For the scopes... probably not... unless you had a frame... and needed a relatively rough source source of +_ 15V, or +5 volts, for an active probe... so probably not.
For the why of the accumulation?... well in my case... I tell myself that I'm interested in the engineering that went into the plug-ins... of which there's plenty of, to learn from...  but, I think the real reason is that they're so darn cute... with all those knobs, dials, and push buttons thingys. (Some people collect stamps, or turtles ... I don't judge.)

#175752

I think I did hear that this happened to someone.? However, a phasing test is simple to do amongst other tests.

Harvey

Show quoted text

On 1/1/2021 11:03 PM, Roy Thistle wrote:
On Fri, Jan  1, 2021 at 06:08 PM, Harvey White wrote:

... needs to make sure that the AC windings [on the frame] are
properly phased and connected...
But why? (Surely, frames didn't leave the factory, with miswired phasing [it's been mentioned plug-in were non-disposable back in the day!] )
And as to all the gremlins, re-arranging the wiring, before the frame hits the GoodWill... is that a thing?
Hands up if that's happened to you.

#175753

If you remember the initial problem, and I think I do, one problem is that the transistors had either broken or missing insulators.? Considering what people can do to "fix" things, some sort of resistance to frame tests seems to be a good idea.

*How* you test for this, and beta, and if the transistors are even properly connected, that's another matter.

All depends on what you do.

Harvey

Show quoted text

On 1/1/2021 11:06 PM, Roy Thistle wrote:
On Fri, Jan  1, 2021 at 06:08 PM, Harvey White wrote:

..the pass transistors were on a nice metal frame that got rid of a lot of heat
easily.? These need to be tested.
Yes... but, do they have to be "tested" by incorporating a "fuse tester" in the tester. Seems inelegant to me.

#175757

Interesting commentary on a test test fixture for TM500 mainframes. it seems there is interest in stuff like this. I'm working on an interface board to enable powering and getting the signal out of a Tek 7000 plugin. Its possibly morphing into a test fixture for them as well. Once its all working I'll share it here.

#175759

I have heard anecdotal evidence that it was something that was occasionally found in early mainframes.
When so many mainframes were produced, I'm sure a few slipped through on a tired Friday afternoon or a hungover Monday morning... :D

A few modules flat out won't work if one phase is miswired, the FG504 is one of these due to how it uses the transformer windings in its onboard power supply.
There is actually a note about it and how to test it in the FG504 manual, so at least Tektronix was aware of the possibility.

Show quoted text

On Sat, Jan  2, 2021 at 01:03 PM, Roy Thistle wrote:


On Fri, Jan  1, 2021 at 06:08 PM, Harvey White wrote:


... needs to make sure that the AC windings [on the frame] are
properly phased and connected...
But why? (Surely, frames didn't leave the factory, with miswired phasing [it's
been mentioned plug-in were non-disposable back in the day!] )
And as to all the gremlins, re-arranging the wiring, before the frame hits the
GoodWill... is that a thing?
Hands up if that's happened to you.

#175761

This is correct. I have an FG504 and such a TM504 that I had to correct the phasing on. The FG504 in trying to reach a +-050VDC rail stacks a 32VDC and a 25VAC on top of each other for both positive and negative rails, and if the 25VAC windings are out of phase it never gets there, so the regulator is below its dropout voltage and you get major hum. 

EJP

#175775

Thank you Harvey!  That is pretty much what I had surmised but I was not sure.  So, I have three function generators and a few DMM etc...  My RTB also has a generator and frequency counter and more.  Clearly, I paid for my RTB, but it seems to have almost everything I've needed to learn and explore SO FAR!

Clearly I laud the effort that went into the project.

Again, thank you Harvey!      larry

#175793

On Fri, Jan  1, 2021 at 08:47 PM, demianm_1 wrote:


I'm working on an interface board to enable powering and getting the signal
out of a Tek 7000 plugin
This had been done, many times... and there is much ink spilled about it, on this forum... and on the Web... that is... if you are mentioning about something (a cable, or board) that plugs into the connector at the back of a bay, in a 7000 frame, and then allows one to attach (and "run/test") a 7000 plug-in.
To see... search this forum on "extender."

#175794

On Fri, Jan  1, 2021 at 11:02 PM, EJP wrote:


I have an FG504 and such a TM504 that I had to correct the phasing on.
If you might indulge a few inquiries...
Did incorrect phasing damage the FG504?
Is that something you did to the TM504?... or was it miswired at the factory... or during a "repair, someone else?"
Do you know... was the TM504... and early manufacture... or a later one?

#175799

A few things are missing from the descriptions.
1. There was a blank module available2. The modules could be user keyed for certain slots3. They could be interconnected unseen in the rear.4. There is/was a high power compartment (mentioned)5. Every module had their own separate power supply6. Uncommitted pass transistors were available for use.
It was a very nice system.? A one bay TM500 module could house a scope current probe for instance.
You could design your own test instrument with the various modules.

We made a laser scanner that mapped the output of a solar cell by position using two function generators, a power supply module, a multimeter and a glue module.? This drove a storage medical display scope from tek and mirror galvanometers.

The glue module selected x and Y modulation, it set the blanking level and x or xy scanning.? Anyway, the modules electronics were minimal.? All of the interconnections were behind the scenes.

Later, we were able to capture the data with a PDP-11 and A/D converters.? The display was then a VT100 with a board and CRT to turn it into a TEK display terminal.
The main purpose was to scan for defects and up the power of a laser to remove the defects.

The 5000 series added IEEE-488 to the mix.? 

take a look here: 

Show quoted text

On Saturday, January 2, 2021, 3:44:30 PM EST, Roy Thistle <roy.thistle@...> wrote:
 
 On Fri, Jan? 1, 2021 at 11:02 PM, EJP wrote:


I have an FG504 and such a TM504 that I had to correct the phasing on.
If you might indulge a few inquiries...
Did incorrect phasing damage the FG504?
Is that something you did to the TM504?... or was it miswired at the factory... or during a "repair, someone else?"
Do you know... was the TM504... and early manufacture... or a later one?

#175807

If you might indulge a few inquiries...
Did incorrect phasing damage the FG504?No. It just caused a large hum at low output levels.

Is that something you did to the TM504?... or was it miswired at the
factory... or during a "repair, someone else?"I fixed it. I'm sure it was done at the factory. Hard to believe it could have been done during a repair: why? The FG504 manual mentions all this as a known problem with some early TM504s. It didn't matter a damn about consistent phasing until someone designed the FG504.

Do you know... was the TM504... and early manufacture... or a later one? I am assuming it was an earlier one. Serial number is inaccessibl without heavy lifting, as there is a fully populated TM506 on top of it. I have a later TM504 that never exhibited the problem. Would have swapped them but I had wired the back panel of that one for three PS503As in series and a DM502.

I mis-spoke earlier when describing the FG504 PSU. It uses the 17.5VAC and two 25VAC windings connected in series after the bridge rectifiers. The +11.5VDC rail also comes into this somehow. I'm not clear why the phasing error causes this problem but it does.

EJP

#175811

Out of about 30 TM 500 power frames I have had 7 that had misphased AC windings in at least one slot, no sign of any post-factory work in them.
Failed pass transistors are pretty common.
I have not seen any misphased AC windings in TM5000 series frames.
-Mac

开云体育

A question from the unwashed relative to: I built a TM500 mainframe tester, and updated the design. Someone might find this useful?