Re: A/R II voltage running up

Kirk Spradling wrote:
>
> Kick myself... Cheap DMM reporting voltages too high. My other DMM
> reports everything A-OK... Arg... Even running low: 4.75vdc. Used a
> PC supply to verify. Cheap DMM reports 6.25 VDC and the R/S DMM I
> bought in 1985 reports 5.125vdc.
>
> How do you calibrate a DMM? Oh well, at least I learned something...
> New LM305 and all is well. I bought some equivalents for $0.25 each.
> Anyone interested?
>
> Kirk S.
> ----- Original Message ----- From: "William Boucher" <boucher@mnsi.net>
> To: <vectorlist@vectorlist.org>
> Sent: Sunday, March 22, 2009 10:09 PM
> Subject: Re: VECTOR: A/R II voltage running up
>
>
>> The 0.1 ohm 7W resistor (R24) is not the issue. It likely looks like
>> it is reading high due to the multimeter lead resistance. Hold the
>> leads together and read that value (call that the zero value), then
>> read across the resistor and subtract the zero value.
>>
>> Obviously enough power is getting through R24, in fact, too much.
>> Check first R29 and R30, the 10 ohm, 1/2W resistors. They are what
>> fail most commonly due to bad edge finger contacts (they burn).
>>
>> Another possible and probable problem could be that either Q2 (TIP32)
>> or Q3 (2N3055) is shorted such that the regulator IC cannot turn down
>> the output voltage because one of them is leaking.
>>
>> If those parts are okay, check that the sense leads are okay (J7 pin
>> 3 for +5V & pin 2 for gnd). Next check R7 (7.5k) and R6 (3.9k).
>> These two resistors in series with 1k pot R8 control the regulator.
>> Check R3 (33 ohm) and R1 (270 ohm). I forget off the top of my head
>> what they do for the regulator. It is entirely possibly that the
>> LM305 regulator (Q1) is shot. Bob Roberts supplies them but hopefully
>> it'll be something simpler than that.
>>
>> If the chips on the main board were really running at 6V... then may
>> the force be with you.
>>
>> William Boucher
>>
>>
>> ----- Original Message ----- From: "Kirk Spradling"
>> <kspradling@kc.rr.com>
>> To: <vectorlist@vectorlist.org>
>> Sent: Sunday, March 22, 2009 10:03 PM
>> Subject: Re: VECTOR: A/R II voltage running up
>>
>>
>>> Pulled one lead of ALL resistors on the +5vdc side and found that
>>> the .1ohm 7watt 3% resistor is showing .45ohm resistance. Does this
>>> need to be a wirewound resistor or will a ceramic work ok? I've
>>> seen several different types, non-inductive is more expensive.
>>>
>>> Recommendations?
>>>
>>> Thanks!
>>>
>>> Kirk S.

Replace the battery...

On most DVMs when the battery gets down to a certain level the voltage &
resistance readings wander around.

Also check the connections of the banana bases inside the the meter -
might have a cold solder joint!

John :-#)#
>>> ----- Original Message ----- From: "Kirk Spradling"
>>> <kspradling@kc.rr.com>
>>> To: <vectorlist@vectorlist.org>
>>> Sent: Sunday, March 22, 2009 4:16 PM
>>> Subject: VECTOR: A/R II voltage running up
>>>
>>>
>>>> Hi,
>>>>
>>>> Rebuilding my Tempest P/S after noticing the voltage was at 6.05
>>>> volts. Attempted to adjust it and could only get down to 5.4vdc.
>>>> Installed the Bob Roberts shotgun repair kit, big blue replacement,
>>>> new pcb and harness connector kit and am still having the same
>>>> issues. Measuring a voltage drop of about 0.125 on the +5vdc from
>>>> P/S to Game PCB and less than .02 on the gnd. No burn marks on the
>>>> pcb and edge connectors are in good shape.
>>>>
>>>> Who knows anything about looking for issues in the feedback system?
>>>> Should I just start lifting resistors in the feedback area and
>>>> taking readings to see if any have gone open? The pot does adjust
>>>> the voltage, it just won't go down any further. Have tested all
>>>> diodes on that side as well.
>>>>
>>>> Thanks,
>>>>
>>>> Kirk S.

-- 
John's Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9 
Call (604)872-5757 or Fax 872-2010 (Pinballs, Jukes, VideoGames)
                 www.flippers.com 
"Old pinballers never die, they just flip out"
---------------------------------------------------------------------------
** Unsubscribe, subscribe, or view the archives at http://www.vectorlist.org
** Please direct other questions, comments, or problems to chris@westnet.com