TI-99/4A Peripheral Expansion Box - Voltages
Does anyone here have much experience with these? I picked one up recently and I've been going over it before plugging things in. I tested the unloaded voltages with the transformer set to 115VAC and got the following on the unregulated DC output rails: +8V rail: 14.4V +16V rail: 25.2V -16V rail: -25.3V It looks like a previous owner had it apart -- there are hand-written labels on the various input taps for the transformer, so I thought that perhaps it was mis-wired on reassembly. But testing the other taps the best result I can get is with the 220VAC tap at approx. +7.5V and +/- 12V on the unregulated outputs. My analog circuits knowledge is pretty thin, so I'm hoping someone here might be able to help out. My questions are: 1) I've measured the output taps from the transformer for each of the various input taps and they match what I'd expect to see as inputs given the various rectified outputs (RMS AC -> Peak AC, minus a diode drop) so I don't *think* the problem is on the power supply board. Am I missing something? The schematic I've been referencing: http://www.mainbyte.com/ti99/schematic/peb_power.jpg (I have the -2 version) 2) Is just a case of not having a load on the outputs causing them to run high? I know that the linear regulators that are likely to be used on any cards can technically handle these inputs, but I wouldn't want to assume that they have heat sinks large enough to dissipate the extra power for very long. 3) Is this actually normal? Thanks in advance for any help.
Just realized I missed a half a sentence (in my defence it's a been a late night). The corrected sentence: 2) Is just a case of not having a load on the outputs causing them to run high? I know that the linear regulators that are likely to be used on any cards can technically handle these inputs, but I wouldn't want to assume that they have heat sinks large enough to dissipate the extra power for very long, so I haven't been brave enough to test the system with cards in it to present a load. Thanks On Sat, Oct 3, 2020 at 7:19 AM Mark Whittington <markwhi@gmail.com> wrote:
Does anyone here have much experience with these? I picked one up recently and I've been going over it before plugging things in. I tested the unloaded voltages with the transformer set to 115VAC and got the following on the unregulated DC output rails:
+8V rail: 14.4V +16V rail: 25.2V -16V rail: -25.3V
It looks like a previous owner had it apart -- there are hand-written labels on the various input taps for the transformer, so I thought that perhaps it was mis-wired on reassembly. But testing the other taps the best result I can get is with the 220VAC tap at approx. +7.5V and +/- 12V on the unregulated outputs.
My analog circuits knowledge is pretty thin, so I'm hoping someone here might be able to help out. My questions are:
1) I've measured the output taps from the transformer for each of the various input taps and they match what I'd expect to see as inputs given the various rectified outputs (RMS AC -> Peak AC, minus a diode drop) so I don't *think* the problem is on the power supply board. Am I missing something?
The schematic I've been referencing: http://www.mainbyte.com/ti99/schematic/peb_power.jpg (I have the -2 version)
2) Is just a case of not having a load on the outputs causing them to run high? I know that the linear regulators that are likely to be used on any cards can technically handle these inputs, but I wouldn't want to assume that they have heat sinks large enough to dissipate the extra power for very long.
3) Is this actually normal?
Thanks in advance for any help.
My experience is with Heathkit, not TI, but on an H8 this would not be unusual on an unloaded chassis. With cards installed the voltages come down. Sent from my iPad
On Oct 3, 2020, at 7:25 AM, Mark Whittington via vcf-midatlantic <vcf-midatlantic@lists.vcfed.org> wrote:
Just realized I missed a half a sentence (in my defence it's a been a late night).
The corrected sentence:
2) Is just a case of not having a load on the outputs causing them to run high? I know that the linear regulators that are likely to be used on any cards can technically handle these inputs, but I wouldn't want to assume that they have heat sinks large enough to dissipate the extra power for very long, so I haven't been brave enough to test the system with cards in it to present a load.
Thanks
On Sat, Oct 3, 2020 at 7:19 AM Mark Whittington <markwhi@gmail.com> wrote:
Does anyone here have much experience with these? I picked one up recently and I've been going over it before plugging things in. I tested the unloaded voltages with the transformer set to 115VAC and got the following on the unregulated DC output rails:
+8V rail: 14.4V +16V rail: 25.2V -16V rail: -25.3V
It looks like a previous owner had it apart -- there are hand-written labels on the various input taps for the transformer, so I thought that perhaps it was mis-wired on reassembly. But testing the other taps the best result I can get is with the 220VAC tap at approx. +7.5V and +/- 12V on the unregulated outputs.
My analog circuits knowledge is pretty thin, so I'm hoping someone here might be able to help out. My questions are:
1) I've measured the output taps from the transformer for each of the various input taps and they match what I'd expect to see as inputs given the various rectified outputs (RMS AC -> Peak AC, minus a diode drop) so I don't *think* the problem is on the power supply board. Am I missing something?
The schematic I've been referencing: http://www.mainbyte.com/ti99/schematic/peb_power.jpg (I have the -2 version)
2) Is just a case of not having a load on the outputs causing them to run high? I know that the linear regulators that are likely to be used on any cards can technically handle these inputs, but I wouldn't want to assume that they have heat sinks large enough to dissipate the extra power for very long.
3) Is this actually normal?
Thanks in advance for any help.
Also I’m assuming you downloaded the manuals and the schematic for the power supply first before plugging in? Sent from: My extremely complicated, hand held electronic device.
On Oct 3, 2020, at 7:24 AM, Mark Whittington via vcf-midatlantic <vcf-midatlantic@lists.vcfed.org> wrote:
Just realized I missed a half a sentence (in my defence it's a been a late night).
The corrected sentence:
2) Is just a case of not having a load on the outputs causing them to run high? I know that the linear regulators that are likely to be used on any cards can technically handle these inputs, but I wouldn't want to assume that they have heat sinks large enough to dissipate the extra power for very long, so I haven't been brave enough to test the system with cards in it to present a load.
Thanks
On Sat, Oct 3, 2020 at 7:19 AM Mark Whittington <markwhi@gmail.com> wrote:
Does anyone here have much experience with these? I picked one up recently and I've been going over it before plugging things in. I tested the unloaded voltages with the transformer set to 115VAC and got the following on the unregulated DC output rails:
+8V rail: 14.4V +16V rail: 25.2V -16V rail: -25.3V
It looks like a previous owner had it apart -- there are hand-written labels on the various input taps for the transformer, so I thought that perhaps it was mis-wired on reassembly. But testing the other taps the best result I can get is with the 220VAC tap at approx. +7.5V and +/- 12V on the unregulated outputs.
My analog circuits knowledge is pretty thin, so I'm hoping someone here might be able to help out. My questions are:
1) I've measured the output taps from the transformer for each of the various input taps and they match what I'd expect to see as inputs given the various rectified outputs (RMS AC -> Peak AC, minus a diode drop) so I don't *think* the problem is on the power supply board. Am I missing something?
The schematic I've been referencing: http://www.mainbyte.com/ti99/schematic/peb_power.jpg (I have the -2 version)
2) Is just a case of not having a load on the outputs causing them to run high? I know that the linear regulators that are likely to be used on any cards can technically handle these inputs, but I wouldn't want to assume that they have heat sinks large enough to dissipate the extra power for very long.
3) Is this actually normal?
Thanks in advance for any help.
Thanks Glenn and Mike for the responses. I did download the schematic, and I found and read the technical information here: http://www.unige.ch/medecine/nouspikel/ti99/pebox.htm before powering the unit, but I was unable to find a manual. If you know where I can find one I'd appreciate a link. I'll check the capacitors and put a load on the various supply rails and see if that brings the voltages down. Thanks again. Mark On Sat, Oct 3, 2020 at 10:10 AM Sentrytv <sentrytv@yahoo.com> wrote:
Also I’m assuming you downloaded the manuals and the schematic for the power supply first before plugging in?
Sent from: My extremely complicated, hand held electronic device.
On Oct 3, 2020, at 7:24 AM, Mark Whittington via vcf-midatlantic < vcf-midatlantic@lists.vcfed.org> wrote:
Just realized I missed a half a sentence (in my defence it's a been a late night).
The corrected sentence:
2) Is just a case of not having a load on the outputs causing them to run high? I know that the linear regulators that are likely to be used on any cards can technically handle these inputs, but I wouldn't want to assume that they have heat sinks large enough to dissipate the extra power for very long, so I haven't been brave enough to test the system with cards in it to present a load.
Thanks
On Sat, Oct 3, 2020 at 7:19 AM Mark Whittington <markwhi@gmail.com> wrote:
Does anyone here have much experience with these? I picked one up recently and I've been going over it before plugging things in. I tested the unloaded voltages with the transformer set to 115VAC and got the following on the unregulated DC output rails:
+8V rail: 14.4V +16V rail: 25.2V -16V rail: -25.3V
It looks like a previous owner had it apart -- there are hand-written labels on the various input taps for the transformer, so I thought that perhaps it was mis-wired on reassembly. But testing the other taps the best result I can get is with the 220VAC tap at approx. +7.5V and +/- 12V on the unregulated outputs.
My analog circuits knowledge is pretty thin, so I'm hoping someone here might be able to help out. My questions are:
1) I've measured the output taps from the transformer for each of the various input taps and they match what I'd expect to see as inputs given the various rectified outputs (RMS AC -> Peak AC, minus a diode drop) so I don't *think* the problem is on the power supply board. Am I missing something?
The schematic I've been referencing: http://www.mainbyte.com/ti99/schematic/peb_power.jpg (I have the -2 version)
2) Is just a case of not having a load on the outputs causing them to run high? I know that the linear regulators that are likely to be used on any cards can technically handle these inputs, but I wouldn't want to assume that they have heat sinks large enough to dissipate the extra power for very long.
3) Is this actually normal?
Thanks in advance for any help.
Mark: I ran that PEB for an hour last week, with no problems. Mike Loewen mloewen@cpumagic.scol.pa.us Old Technology http://q7.neurotica.com/Oldtech/ On Sat, 3 Oct 2020, Mark Whittington via vcf-midatlantic wrote:
Thanks Glenn and Mike for the responses.
I did download the schematic, and I found and read the technical information here: http://www.unige.ch/medecine/nouspikel/ti99/pebox.htm before powering the unit, but I was unable to find a manual. If you know where I can find one I'd appreciate a link.
I'll check the capacitors and put a load on the various supply rails and see if that brings the voltages down.
Thanks again.
Mark
On Sat, Oct 3, 2020 at 10:10 AM Sentrytv <sentrytv@yahoo.com> wrote:
Also I?m assuming you downloaded the manuals and the schematic for the power supply first before plugging in?
Sent from: My extremely complicated, hand held electronic device.
On Oct 3, 2020, at 7:24 AM, Mark Whittington via vcf-midatlantic < vcf-midatlantic@lists.vcfed.org> wrote:
Just realized I missed a half a sentence (in my defence it's a been a late night).
The corrected sentence:
2) Is just a case of not having a load on the outputs causing them to run high? I know that the linear regulators that are likely to be used on any cards can technically handle these inputs, but I wouldn't want to assume that they have heat sinks large enough to dissipate the extra power for very long, so I haven't been brave enough to test the system with cards in it to present a load.
Thanks
On Sat, Oct 3, 2020 at 7:19 AM Mark Whittington <markwhi@gmail.com> wrote:
Does anyone here have much experience with these? I picked one up recently and I've been going over it before plugging things in. I tested the unloaded voltages with the transformer set to 115VAC and got the following on the unregulated DC output rails:
+8V rail: 14.4V +16V rail: 25.2V -16V rail: -25.3V
It looks like a previous owner had it apart -- there are hand-written labels on the various input taps for the transformer, so I thought that perhaps it was mis-wired on reassembly. But testing the other taps the best result I can get is with the 220VAC tap at approx. +7.5V and +/- 12V on the unregulated outputs.
My analog circuits knowledge is pretty thin, so I'm hoping someone here might be able to help out. My questions are:
1) I've measured the output taps from the transformer for each of the various input taps and they match what I'd expect to see as inputs given the various rectified outputs (RMS AC -> Peak AC, minus a diode drop) so I don't *think* the problem is on the power supply board. Am I missing something?
The schematic I've been referencing: http://www.mainbyte.com/ti99/schematic/peb_power.jpg (I have the -2 version)
2) Is just a case of not having a load on the outputs causing them to run high? I know that the linear regulators that are likely to be used on any cards can technically handle these inputs, but I wouldn't want to assume that they have heat sinks large enough to dissipate the extra power for very long.
3) Is this actually normal?
Thanks in advance for any help.
Hey Mike, I appreciate the info. I'm sure it'll work -- the expansion cards all have their own voltage regulators, and they're expecting unregulated voltage from the PEB. The apparent problem is that the PEB's unregulated voltage rails are way out of spec -- the 8v rail is running at 14.4v, and the +/- 16v rails are running at +/-25v. While the voltage regulators in the expansion cards /can/ regulate those voltages down to 5, 12 and -12, and the cards will work, they're going to be dissipating a lot more power than they're designed for. It may be that there's actually no problem at all -- under load the voltages might come down to within the expected ranges. I'm going to test that this evening. I didn't suspect that you'd sold me a broken box :) The console itself works great. I just want to make sure that the system is going to continue to work for another 30 years before I start using it for hours at a time! Best, Mark On Sat, Oct 3, 2020 at 3:41 PM Mike Loewen via vcf-midatlantic < vcf-midatlantic@lists.vcfed.org> wrote:
Mark:
I ran that PEB for an hour last week, with no problems.
Mike Loewen mloewen@cpumagic.scol.pa.us Old Technology http://q7.neurotica.com/Oldtech/
On Sat, 3 Oct 2020, Mark Whittington via vcf-midatlantic wrote:
Thanks Glenn and Mike for the responses.
I did download the schematic, and I found and read the technical information here: http://www.unige.ch/medecine/nouspikel/ti99/pebox.htm before powering the unit, but I was unable to find a manual. If you know where I can find one I'd appreciate a link.
I'll check the capacitors and put a load on the various supply rails and see if that brings the voltages down.
Thanks again.
Mark
On Sat, Oct 3, 2020 at 10:10 AM Sentrytv <sentrytv@yahoo.com> wrote:
Also I?m assuming you downloaded the manuals and the schematic for the power supply first before plugging in?
Sent from: My extremely complicated, hand held electronic device.
On Oct 3, 2020, at 7:24 AM, Mark Whittington via vcf-midatlantic < vcf-midatlantic@lists.vcfed.org> wrote:
Just realized I missed a half a sentence (in my defence it's a been a late night).
The corrected sentence:
2) Is just a case of not having a load on the outputs causing them to run high? I know that the linear regulators that are likely to be used on any cards can technically handle these inputs, but I wouldn't want to assume that they have heat sinks large enough to dissipate the extra power for very long, so I haven't been brave enough to test the system with cards in it to present a load.
Thanks
On Sat, Oct 3, 2020 at 7:19 AM Mark Whittington <markwhi@gmail.com> wrote:
Does anyone here have much experience with these? I picked one up recently and I've been going over it before plugging things in. I tested the unloaded voltages with the transformer set to 115VAC and got the following on the unregulated DC output rails:
+8V rail: 14.4V +16V rail: 25.2V -16V rail: -25.3V
It looks like a previous owner had it apart -- there are hand-written labels on the various input taps for the transformer, so I thought that perhaps it was mis-wired on reassembly. But testing the other taps the best result I can get is with the 220VAC tap at approx. +7.5V and +/- 12V on the unregulated outputs.
My analog circuits knowledge is pretty thin, so I'm hoping someone here might be able to help out. My questions are:
1) I've measured the output taps from the transformer for each of the various input taps and they match what I'd expect to see as inputs given the various rectified outputs (RMS AC -> Peak AC, minus a diode drop) so I don't *think* the problem is on the power supply board. Am I missing something?
The schematic I've been referencing: http://www.mainbyte.com/ti99/schematic/peb_power.jpg (I have the -2 version)
2) Is just a case of not having a load on the outputs causing them to run high? I know that the linear regulators that are likely to be used on any cards can technically handle these inputs, but I wouldn't want to assume that they have heat sinks large enough to dissipate the extra power for very long.
3) Is this actually normal?
Thanks in advance for any help.
I’ve used a load anywhere from 100 to 20 ohms at least 10 watts for computer power supply, 100 ohms @10w should be fine per 5v and 12v rails each to ground. So for the TI the same would apply 8 V and 16 V. Power supply The PE-box provides unregulated power, meant to be used by voltage regulators intalled on each card. Typically, these would be a 78x05 (+5V) , a 78x12 (+12V) or a 79x12 (-12V). According to the specs, these regulators need an input voltage at least 3V in excess of the required output voltage. Therefore, the PE-box supplies them with +16V, -16V and +8V. Note that if you need -5V, you could use a 79x05 and feed it with the -16V supply. This would just mean that you need a really big heat sink, since this regulator is going to dissipate a lot of power... When I actually get to my computer I will look to see what I have for manuals. Sent from: My extremely complicated, hand held electronic device.
On Oct 3, 2020, at 2:10 PM, Mark Whittington <markwhi@gmail.com> wrote:
Thanks Glenn and Mike for the responses.
I did download the schematic, and I found and read the technical information here: http://www.unige.ch/medecine/nouspikel/ti99/pebox.htm before powering the unit, but I was unable to find a manual. If you know where I can find one I'd appreciate a link.
I'll check the capacitors and put a load on the various supply rails and see if that brings the voltages down.
Thanks again.
Mark
On Sat, Oct 3, 2020 at 10:10 AM Sentrytv <sentrytv@yahoo.com> wrote: Also I’m assuming you downloaded the manuals and the schematic for the power supply first before plugging in?
Sent from: My extremely complicated, hand held electronic device.
On Oct 3, 2020, at 7:24 AM, Mark Whittington via vcf-midatlantic <vcf-midatlantic@lists.vcfed.org> wrote:
Just realized I missed a half a sentence (in my defence it's a been a late night).
The corrected sentence:
2) Is just a case of not having a load on the outputs causing them to run high? I know that the linear regulators that are likely to be used on any cards can technically handle these inputs, but I wouldn't want to assume that they have heat sinks large enough to dissipate the extra power for very long, so I haven't been brave enough to test the system with cards in it to present a load.
Thanks
On Sat, Oct 3, 2020 at 7:19 AM Mark Whittington <markwhi@gmail.com> wrote:
Does anyone here have much experience with these? I picked one up recently and I've been going over it before plugging things in. I tested the unloaded voltages with the transformer set to 115VAC and got the following on the unregulated DC output rails:
+8V rail: 14.4V +16V rail: 25.2V -16V rail: -25.3V
It looks like a previous owner had it apart -- there are hand-written labels on the various input taps for the transformer, so I thought that perhaps it was mis-wired on reassembly. But testing the other taps the best result I can get is with the 220VAC tap at approx. +7.5V and +/- 12V on the unregulated outputs.
My analog circuits knowledge is pretty thin, so I'm hoping someone here might be able to help out. My questions are:
1) I've measured the output taps from the transformer for each of the various input taps and they match what I'd expect to see as inputs given the various rectified outputs (RMS AC -> Peak AC, minus a diode drop) so I don't *think* the problem is on the power supply board. Am I missing something?
The schematic I've been referencing: http://www.mainbyte.com/ti99/schematic/peb_power.jpg (I have the -2 version)
2) Is just a case of not having a load on the outputs causing them to run high? I know that the linear regulators that are likely to be used on any cards can technically handle these inputs, but I wouldn't want to assume that they have heat sinks large enough to dissipate the extra power for very long.
3) Is this actually normal?
Thanks in advance for any help.
Thanks Mike! I don't have any power resistors in my junk bin, but a friend of mine does and I'm going to pick them up tonight and test the power supply under load. I'll reply again once I have the results of load testing. Cheers, Mark On Sat, Oct 3, 2020 at 3:48 PM Sentrytv <sentrytv@yahoo.com> wrote:
I’ve used a load anywhere from 100 to 20 ohms at least 10 watts for computer power supply, 100 ohms @10w should be fine per 5v and 12v rails each to ground. So for the TI the same would apply 8 V and 16 V. Power supply
The PE-box provides unregulated power, meant to be used by voltage regulators intalled on each card. Typically, these would be a 78x05 (+5V) , a 78x12 (+12V) or a 79x12 (-12V). According to the specs, these regulators need an input voltage at least 3V in excess of the required output voltage. Therefore, the PE-box supplies them with +16V, -16V and +8V. Note that if you need -5V, you could use a 79x05 and feed it with the -16V supply. This would just mean that you need a really big heat sink, since this regulator is going to dissipate a lot of power...
When I actually get to my computer I will look to see what I have for manuals.
Sent from: My extremely complicated, hand held electronic device.
On Oct 3, 2020, at 2:10 PM, Mark Whittington <markwhi@gmail.com> wrote:
Thanks Glenn and Mike for the responses.
I did download the schematic, and I found and read the technical information here: http://www.unige.ch/medecine/nouspikel/ti99/pebox.htm before powering the unit, but I was unable to find a manual. If you know where I can find one I'd appreciate a link.
I'll check the capacitors and put a load on the various supply rails and see if that brings the voltages down.
Thanks again.
Mark
On Sat, Oct 3, 2020 at 10:10 AM Sentrytv <sentrytv@yahoo.com> wrote:
Also I’m assuming you downloaded the manuals and the schematic for the power supply first before plugging in?
Sent from: My extremely complicated, hand held electronic device.
On Oct 3, 2020, at 7:24 AM, Mark Whittington via vcf-midatlantic < vcf-midatlantic@lists.vcfed.org> wrote:
Just realized I missed a half a sentence (in my defence it's a been a late night).
The corrected sentence:
2) Is just a case of not having a load on the outputs causing them to run high? I know that the linear regulators that are likely to be used on any cards can technically handle these inputs, but I wouldn't want to assume that they have heat sinks large enough to dissipate the extra power for very long, so I haven't been brave enough to test the system with cards in it to present a load.
Thanks
On Sat, Oct 3, 2020 at 7:19 AM Mark Whittington <markwhi@gmail.com> wrote:
Does anyone here have much experience with these? I picked one up recently and I've been going over it before plugging things in. I tested the unloaded voltages with the transformer set to 115VAC and got the following on the unregulated DC output rails:
+8V rail: 14.4V +16V rail: 25.2V -16V rail: -25.3V
It looks like a previous owner had it apart -- there are hand-written labels on the various input taps for the transformer, so I thought that perhaps it was mis-wired on reassembly. But testing the other taps the best result I can get is with the 220VAC tap at approx. +7.5V and +/- 12V on the unregulated outputs.
My analog circuits knowledge is pretty thin, so I'm hoping someone here might be able to help out. My questions are:
1) I've measured the output taps from the transformer for each of the various input taps and they match what I'd expect to see as inputs given the various rectified outputs (RMS AC -> Peak AC, minus a diode drop) so I don't *think* the problem is on the power supply board. Am I missing something?
The schematic I've been referencing: http://www.mainbyte.com/ti99/schematic/peb_power.jpg (I have the -2 version)
2) Is just a case of not having a load on the outputs causing them to run high? I know that the linear regulators that are likely to be used on any cards can technically handle these inputs, but I wouldn't want to assume that they have heat sinks large enough to dissipate the extra power for very long.
3) Is this actually normal?
Thanks in advance for any help.
Definitely look at the link that I sent you for the power supply diagram and of course other diagrams as well before you power the box up again so you can be 100% sure you’re Checking it correctly Mike Rosen Sent from: My extremely complicated, hand held electronic device.
On Oct 3, 2020, at 4:32 PM, Mark Whittington <markwhi@gmail.com> wrote:
Thanks Mike! I don't have any power resistors in my junk bin, but a friend of mine does and I'm going to pick them up tonight and test the power supply under load. I'll reply again once I have the results of load testing.
Cheers,
Mark
On Sat, Oct 3, 2020 at 3:48 PM Sentrytv <sentrytv@yahoo.com> wrote: I’ve used a load anywhere from 100 to 20 ohms at least 10 watts for computer power supply, 100 ohms @10w should be fine per 5v and 12v rails each to ground. So for the TI the same would apply 8 V and 16 V. Power supply
The PE-box provides unregulated power, meant to be used by voltage regulators intalled on each card. Typically, these would be a 78x05 (+5V) , a 78x12 (+12V) or a 79x12 (-12V). According to the specs, these regulators need an input voltage at least 3V in excess of the required output voltage. Therefore, the PE-box supplies them with +16V, -16V and +8V. Note that if you need -5V, you could use a 79x05 and feed it with the -16V supply. This would just mean that you need a really big heat sink, since this regulator is going to dissipate a lot of power...
When I actually get to my computer I will look to see what I have for manuals.
Sent from: My extremely complicated, hand held electronic device.
On Oct 3, 2020, at 2:10 PM, Mark Whittington <markwhi@gmail.com> wrote:
Thanks Glenn and Mike for the responses.
I did download the schematic, and I found and read the technical information here: http://www.unige.ch/medecine/nouspikel/ti99/pebox.htm before powering the unit, but I was unable to find a manual. If you know where I can find one I'd appreciate a link.
I'll check the capacitors and put a load on the various supply rails and see if that brings the voltages down.
Thanks again.
Mark
On Sat, Oct 3, 2020 at 10:10 AM Sentrytv <sentrytv@yahoo.com> wrote: Also I’m assuming you downloaded the manuals and the schematic for the power supply first before plugging in?
Sent from: My extremely complicated, hand held electronic device.
On Oct 3, 2020, at 7:24 AM, Mark Whittington via vcf-midatlantic <vcf-midatlantic@lists.vcfed.org> wrote:
Just realized I missed a half a sentence (in my defence it's a been a late night).
The corrected sentence:
2) Is just a case of not having a load on the outputs causing them to run high? I know that the linear regulators that are likely to be used on any cards can technically handle these inputs, but I wouldn't want to assume that they have heat sinks large enough to dissipate the extra power for very long, so I haven't been brave enough to test the system with cards in it to present a load.
Thanks
On Sat, Oct 3, 2020 at 7:19 AM Mark Whittington <markwhi@gmail.com> wrote:
Does anyone here have much experience with these? I picked one up recently and I've been going over it before plugging things in. I tested the unloaded voltages with the transformer set to 115VAC and got the following on the unregulated DC output rails:
+8V rail: 14.4V +16V rail: 25.2V -16V rail: -25.3V
It looks like a previous owner had it apart -- there are hand-written labels on the various input taps for the transformer, so I thought that perhaps it was mis-wired on reassembly. But testing the other taps the best result I can get is with the 220VAC tap at approx. +7.5V and +/- 12V on the unregulated outputs.
My analog circuits knowledge is pretty thin, so I'm hoping someone here might be able to help out. My questions are:
1) I've measured the output taps from the transformer for each of the various input taps and they match what I'd expect to see as inputs given the various rectified outputs (RMS AC -> Peak AC, minus a diode drop) so I don't *think* the problem is on the power supply board. Am I missing something?
The schematic I've been referencing: http://www.mainbyte.com/ti99/schematic/peb_power.jpg (I have the -2 version)
2) Is just a case of not having a load on the outputs causing them to run high? I know that the linear regulators that are likely to be used on any cards can technically handle these inputs, but I wouldn't want to assume that they have heat sinks large enough to dissipate the extra power for very long.
3) Is this actually normal?
Thanks in advance for any help.
participants (4)
-
Glenn Roberts -
Mark Whittington -
Mike Loewen -
Sentrytv