Lynx Mrk II - Q7 and Q8 transistors - PNP or NPN?

[Rossoe]

For sanity sake can someone please confirm that Q7 is PNP and Q8 is a NPN?

 

Looking at schematics here - https://wiki.console5.com/tw/images/7/79/Atari-Lynx-II-Schematic-%28Hayato%29-C104247-6-29-90.png

and both look like they should be PNP - but the figures I've recorded suggest otherwise?

 

I'm fairly new to electronics so not totally confident of my analysis.

 

Lynx in question is a Mrk II - C104424-001

 

Below are the figures I get with my multimeter in diode mode - power off.

 

Q7

PNP?

 

 

Q8 
NPN?

 

 

 

Edited January 9, 2023 by Rossoe

[sage]

The are both labelled as 2N3906, thus PNP

 

https://en.wikipedia.org/wiki/2N3906

[Rossoe]

ok so what's going on with the figures I'm getting - Q7 & Q8 definitely don't match up to each other? if they break or malfunction can they behave in odd ways like this?

 

both transistors have been changed out for new parts using kits sold to re-do the power circuit. So to avoid confusion I opened a second MKII Lynx which has never been opened before and checked the same parts -

Figures are similar to the first machine with Q8 behaving more like an NPN ??

[+karri]

I have had a Lynx where this transistor Q8 was broken. And also a Lynx where the 4069 chip was bad and it looked weird when I measured stuff.

[Rossoe]

Sure, I kind of expected to have issues with the first Lynx, as I'd tried to install a BennVenn screen and blown a diode on MB etc. but opening a 2nd working Lynx and getting similar figures threw me off! if the 2nd one also has a broken transistor on Q8 it's impressive it still works ok?

 

Is there a chance you can get different readings when testing transistors in circuit vs out of circuit? 

Edited January 9, 2023 by Rossoe

[+Stephen Moss]

You cannot be 100% certain of the accuracy of readings you get when measuring in circuit as the are often components in parallel with the measurement that will affect the outcome, so a voltage measurement can often be of more help.

 

For what it is worth with my meter on the diode setting and no voltage source connected on my Lynx 2...

For Q7 I get a reading 0.704 for both Base-Collector & Base-Emitter readings (GND lead to Base) + a reading of High impedance for both Base-Collector & Base-Emitter (V lead to Base)

 

For Q8 I get a reading 0.603 for Base-Collector & 0.202 for Base-Emitter readings (GND lead to Base) + a reading of High impedance for Base-Collector & 0.202 for Base-Emitter (V lead to Base), but the Base-Emitter reading will of course be affected due to R74 effectively being across the junction.  

 

17 hours ago, Rossoe said:

For sanity sake can someone please confirm that Q7 is PNP and Q8 is a NPN?

The schematic symbol should tell you, with bipolar transistors like these it is simple, just look at the direction of the arrow on the Emitter, NPN = Not Pointing iN, so away from the Base.

[Rossoe]

Thanks for testing your Lynx - Is this the orientation re Base, Emitter and Collector?

[+Stephen Moss]

Yes, that is the correct orientation according to the data sheet for this device which I believe is the same/an equivalent device.