Large Speedball Board Failed Resistance Test [resolved]

charlie.waid · 828

0 Members and 1 Guest are viewing this topic.

Offline charlie.waid

  • Newbie
  • *
    • Posts: 3
You can check for continuity between pairs of transistor legs with your meter. A shorted transistor would tend to pass a lot more current than is desirable, but your board isn't passing any.

Found this mentioned in another thread but seems like I may have a different issue. When trying to perform a continuity test on the transistor leg pairs, I get no tone. I went back and reviewed page 22 on how to assemble the transistor to the heat sink but am unsure where I would have gone wrong there.

I am unsure how to proceed, any advice greatly appreciated. What kind of info/pics would I need to provide to give more info on my situation ?
« Last Edit: March 23, 2023, 04:36:00 PM by Paul Birkeland »



Offline Paul Birkeland

  • Global Moderator
  • Hero Member
  • *****
    • Posts: 19410
Reply #1 on: March 23, 2023, 04:19:55 AM
When trying to perform a continuity test on the transistor leg pairs, I get no tone.
That would mean your transistor hasn't failed.  Which test in the manual are you not passing?

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline charlie.waid

  • Newbie
  • *
    • Posts: 3
Reply #2 on: March 23, 2023, 08:35:02 AM
Failing the resistance check at the bottom of page 29.

12u to OA and OB do not move the meter I am using at all (Klein Tools MM325)



Offline Doc B.

  • Administrator
  • Hero Member
  • *****
    • Posts: 9572
    • Bottlehead
Reply #3 on: March 23, 2023, 09:29:55 AM
On many meters the continuity tone function only works below about 200 ohms resistance. Most of the transistors we use read around 500 ohms to 1.5K ohms in the forward direction (and infinity or very high megohms in the reverse direction). So the best bet is to read the meter rather than relying upon the beeper. As PB implies, if you hear the tone the transistor may actually be shorted. At that point you swap the test leads on that pair of legs to see if the tone occurs with the current flow reversed. If it does the transistor is toast or possibly there is a short in the circuit that is parallel with the transistor.

Dan "Doc B." Schmalle
President For Life
Bottlehead Corp.


Offline Paul Birkeland

  • Global Moderator
  • Hero Member
  • *****
    • Posts: 19410
Reply #4 on: March 23, 2023, 02:58:21 PM
Set your meter on the 2M resistance setting and see what appears with that setting.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline charlie.waid

  • Newbie
  • *
    • Posts: 3
Reply #5 on: March 23, 2023, 04:06:29 PM
Not sure what I did differently this time but reconnected everything and got a proper reading! Was just shy of 200k ohms on both OA and OB. Everything checks out now (and sounds great), sorry for the false alarm.

Thanks for your patience. The documentation for this thing has been great

How should I go about closing this thread?



Offline JohnnyT

  • Jr. Member
  • **
    • Posts: 13
Reply #6 on: April 07, 2023, 06:01:04 AM
Hi, I'm in the process of upgrading my Crack with the Speedball and have a similar issue for the large Speedball board. For the resistance checks on OA and OB my Klein DMM always reads OL, so no continuity or infinite resistance. I tried different probes and tried using the alligator clips, no matter what I try it always reads OL. It's on auto-ranging mode, and when I touch the red probe to OA or OB, I notice that it auto-ranges up to the Megaohms but then says OL at the end. I double-checked all the soldered joints are secure. 3U is soldered to G (black), 4U is soldered to B+ (red), 9U is soldered to 0A (white), and 7U is soldered to OB (white). So I don't know how to proceed. Is there an alternate location I could attach the black clip of the DMM or is 12U the only point? My 12U joint is a bit cluttered so not a lot of surface area to clip onto, but it worked for the small board voltage tests (and the stock Crack tests). Thanks

Note: My stock Crack was working without any problems before.
« Last Edit: April 07, 2023, 06:04:08 AM by JohnnyT »



Offline Paul Birkeland

  • Global Moderator
  • Hero Member
  • *****
    • Posts: 19410
Reply #7 on: April 07, 2023, 06:02:06 AM
For the resistance checks on OA and OB my Klein DMM always reads OL, so no continuity or infinite resistance
OL is "Over Limit" which is infinite resistance.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline JohnnyT

  • Jr. Member
  • **
    • Posts: 13
Reply #8 on: April 07, 2023, 06:07:20 AM
OL is "Over Limit" which is infinite resistance.

Ok, thanks. Is that acceptable or should I be getting something in the range of kiloOhms? I understood that the only problem would be if the resistance was low (<100ohm).

Update: I checked and my DMM is a Klein MM420 (can measure up to 50 MOhms).
« Last Edit: April 07, 2023, 06:11:58 AM by JohnnyT »



Offline Paul Birkeland

  • Global Moderator
  • Hero Member
  • *****
    • Posts: 19410
Reply #9 on: April 07, 2023, 06:31:15 AM
I understood that the only problem would be if the resistance was low (<100ohm).
Yes, that is the only problem we are looking for with this test, not wither you have fifty million ohms or infinite ohms.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline JohnnyT

  • Jr. Member
  • **
    • Posts: 13
Reply #10 on: April 07, 2023, 09:42:35 AM
Yes, that is the only problem we are looking for with this test, not wither you have fifty million ohms or infinite ohms.

Great, thanks! I passed the voltage checks. It's sounding awesome.