Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

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Old December 1st 19, 06:00 PM posted to sci.electronics.repair
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Default Voltages too far out of spec?

Gentlemen,

On the HP audio spectrum analyser I'm now working on, I've found all the
low voltage regs seem fine (sub 30V I mean) within a few hundredths of a
volt to what they should be. The medium voltages are not so close to what
those printed on the PCB state they should be, however. I've got points
on the board that are supposed to be 150V reading 170V and (less far out)
an 80V rail reading 84V. 150 reading 170 seems to me to indicate a
regulator gone short, possibly. Anyway, question No.1 is: has anyone
encountered readings that were this far out from those stated but which
turned out to be nothing to worry about in the end?
Question No.2 is: should I investigate the 80V -- 84V anomaly?



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Old December 1st 19, 07:38 PM posted to sci.electronics.repair
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Default Voltages too far out of spec?

On 2019/12/01 9:00 a.m., Cursitor Doom wrote:
Gentlemen,

On the HP audio spectrum analyser I'm now working on, I've found all the
low voltage regs seem fine (sub 30V I mean) within a few hundredths of a
volt to what they should be. The medium voltages are not so close to what
those printed on the PCB state they should be, however. I've got points
on the board that are supposed to be 150V reading 170V and (less far out)
an 80V rail reading 84V. 150 reading 170 seems to me to indicate a
regulator gone short, possibly. Anyway, question No.1 is: has anyone
encountered readings that were this far out from those stated but which
turned out to be nothing to worry about in the end?
Question No.2 is: should I investigate the 80V -- 84V anomaly?




On the HP schematic notes what was the VOM loading factor? Back in the
day 100K Ohms/volt (analog meter) was not unusual so your
"over-voltages" may simply be the result of under-loading the circuit
with your modern DVM.

John :-#)#
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Old December 1st 19, 08:02 PM posted to sci.electronics.repair
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First recorded activity by DIYBanter: Dec 2017
Posts: 466
Default Voltages too far out of spec?

On 12/1/19 12:38 PM, John Robertson wrote:
On 2019/12/01 9:00 a.m., Cursitor Doom wrote:
Gentlemen,

On the HP audio spectrum analyser I'm now working on, I've found all the
low voltage regs seem fine (sub 30V I mean) within a few hundredths of a
volt to what they should be. The medium voltages are not so close to what
those printed on the PCB state they should be, however. I've got points
on the board that are supposed to be 150V reading 170V and (less far out)
an 80V rail reading 84V. 150 reading 170 seems to me to indicate a
regulator gone short, possibly. Anyway, question No.1 is: has anyone
encountered readings that were this far out from those stated but which
turned out to be nothing to worry about in the end?
Question No.2 is: should I investigate the 80V -- 84V anomaly?




On the HP schematic notes what was the VOM loading factor? Back in the
day 100K Ohms/volt (analog meter) was not unusual so your
"over-voltages" may simply be the result of under-loading the circuit
with your modern DVM.

John :-#)#


If a power supply voltage can be loaded down by a 10-20 Meg resistance,
there's something seriously wrong with the supply.


--
"I am a river to my people."
Jeff-1.0
WA6FWi
http:foxsmercantile.com
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Old December 1st 19, 08:29 PM posted to sci.electronics.repair
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Posts: 802
Default Voltages too far out of spec?

On 2019/12/01 11:02 a.m., Fox's Mercantile wrote:
On 12/1/19 12:38 PM, John Robertson wrote:
On 2019/12/01 9:00 a.m., Cursitor Doom wrote:
Gentlemen,

On the HP audio spectrum analyser I'm now working on, I've found all the
low voltage regs seem fine (sub 30V I mean) within a few hundredths of a
volt to what they should be. The medium voltages are not so close to
what
those printed on the PCB state they should be, however. I've got points
on the board that are supposed to be 150V reading 170V and (less far
out)
an 80V rail reading 84V. 150 reading 170 seems to me to indicate a
regulator gone short, possibly. Anyway, question No.1 is: has anyone
encountered readings that were this far out from those stated but which
turned out to be nothing to worry about in the end?
Question No.2 is: should I investigate the 80V -- 84V anomaly?




On the HP schematic notes what was the VOM loading factor? Back in the
day 100K Ohms/volt (analog meter) was not unusual so your
"over-voltages" may simply be the result of under-loading the circuit
with your modern DVM.

John :-#)#


If a* power supply voltage can be loaded down by a 10-20 Meg resistance,
there's something seriously wrong with the supply.



Sorry, I believe I was thinking of 1000 Ohms/V meter when I was speaking
of loading.

https://www.allaboutcircuits.com/tex...sured-circuit/

Spoiled by DMMs one gets rusty on one's assumptions.

Thanks!

John :-#)#

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Old December 1st 19, 08:36 PM posted to sci.electronics.repair
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Posts: 121
Default Voltages too far out of spec?

On 2/12/2019 4:00 am, Cursitor Doom wrote:
Gentlemen,

On the HP audio spectrum analyser I'm now working on, I've found all the
low voltage regs seem fine (sub 30V I mean) within a few hundredths of a
volt to what they should be. The medium voltages are not so close to what
those printed on the PCB state they should be, however. I've got points
on the board that are supposed to be 150V reading 170V and (less far out)
an 80V rail reading 84V. 150 reading 170 seems to me to indicate a
regulator gone short, possibly. Anyway, question No.1 is: has anyone
encountered readings that were this far out from those stated but which
turned out to be nothing to worry about in the end?
Question No.2 is: should I investigate the 80V -- 84V anomaly?




**Are the Voltages that are out of whack at the end of a Voltage
regulator, or are they unregulated Voltages? Is yours mains supply bang
on spec?

--
Trevor Wilson
www.rageaudio.com.au


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Old December 1st 19, 08:37 PM posted to sci.electronics.repair
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Posts: 380
Default Voltages too far out of spec?

On Sunday, December 1, 2019 at 12:00:21 PM UTC-5, Cursitor Doom wrote:
The medium voltages are not so close to what
those printed on the PCB state they should be, however.


Over the years, I've seen voltages printed on PCs that were incorrect for the version of board as loaded. IOW, manufacturers will often make running changes to a product design and revise parts loaded on the board and even use a different transformer to feed it. Since they have may have boards already screened, they're not going to scrap them out.

If HP has archived schematics, they may have a revised schematic that more closely or even exactly matches the voltages you're encountering.
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Old December 1st 19, 08:53 PM posted to sci.electronics.repair
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Posts: 466
Default Voltages too far out of spec?

On 12/1/19 1:29 PM, John Robertson wrote:
On 2019/12/01 11:02 a.m., Fox's Mercantile wrote:
On 12/1/19 12:38 PM, John Robertson wrote:
On 2019/12/01 9:00 a.m., Cursitor Doom wrote:
Gentlemen,

On the HP audio spectrum analyser I'm now working on, I've found all
the
low voltage regs seem fine (sub 30V I mean) within a few hundredths
of a
volt to what they should be. The medium voltages are not so close to
what
those printed on the PCB state they should be, however. I've got points
on the board that are supposed to be 150V reading 170V and (less far
out)
an 80V rail reading 84V. 150 reading 170 seems to me to indicate a
regulator gone short, possibly. Anyway, question No.1 is: has anyone
encountered readings that were this far out from those stated but which
turned out to be nothing to worry about in the end?
Question No.2 is: should I investigate the 80V -- 84V anomaly?




On the HP schematic notes what was the VOM loading factor? Back in
the day 100K Ohms/volt (analog meter) was not unusual so your
"over-voltages" may simply be the result of under-loading the circuit
with your modern DVM.

John :-#)#


If a* power supply voltage can be loaded down by a 10-20 Meg resistance,
there's something seriously wrong with the supply.



Sorry, I believe I was thinking of 1000 Ohms/V meter when I was speaking
of loading.

https://www.allaboutcircuits.com/tex...sured-circuit/


Spoiled by DMMs one gets rusty on one's assumptions.

Thanks!

John :-#)#


Even so, a 100K load shouldn't load down a power supply.


--
"I am a river to my people."
Jeff-1.0
WA6FWi
http:foxsmercantile.com
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Old December 2nd 19, 02:15 AM posted to sci.electronics.repair
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First recorded activity by DIYBanter: Jul 2006
Posts: 802
Default Voltages too far out of spec?

On 2019/12/01 11:53 a.m., Fox's Mercantile wrote:
On 12/1/19 1:29 PM, John Robertson wrote:
On 2019/12/01 11:02 a.m., Fox's Mercantile wrote:
On 12/1/19 12:38 PM, John Robertson wrote:
On 2019/12/01 9:00 a.m., Cursitor Doom wrote:
Gentlemen,

On the HP audio spectrum analyser I'm now working on, I've found
all the
low voltage regs seem fine (sub 30V I mean) within a few hundredths
of a
volt to what they should be. The medium voltages are not so close
to what
those printed on the PCB state they should be, however. I've got
points
on the board that are supposed to be 150V reading 170V and (less
far out)
an 80V rail reading 84V. 150 reading 170 seems to me to indicate a
regulator gone short, possibly. Anyway, question No.1 is: has anyone
encountered readings that were this far out from those stated but
which
turned out to be nothing to worry about in the end?
Question No.2 is: should I investigate the 80V -- 84V anomaly?




On the HP schematic notes what was the VOM loading factor? Back in
the day 100K Ohms/volt (analog meter) was not unusual so your
"over-voltages" may simply be the result of under-loading the
circuit with your modern DVM.

John :-#)#

If a* power supply voltage can be loaded down by a 10-20 Meg resistance,
there's something seriously wrong with the supply.



Sorry, I believe I was thinking of 1000 Ohms/V meter when I was
speaking of loading.

https://www.allaboutcircuits.com/tex...sured-circuit/


Spoiled by DMMs one gets rusty on one's assumptions.

Thanks!

John :-#)#


Even so, a 100K load shouldn't load down a power supply.



I do recall schematics of old (mostly tube equipment) warning people
that the readings were done with a specific Ohms/Volt meter and that
readings would vary accordingly.

Mostly it is something to keep in the back of your mind when reading
schematics and voltage test points...

Nice chatting with you!

John :-#)#



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