MVP-861 display out after cleaning laser and belt change.

[macman007]

See Post #23. Mods, feel free to delete this post.

[Cohibaman]

If I read that correctly, you have the proper voltage at the regulator, but no further, correct? That suggests one of three things;

1) Bad solder joint at the regulator
2) Bad solder joint at J1 connector
3) Bad trace from the regulator to J1 connector

I’d heat up the solder joints on Q18 and J1 connector.

[macman007]

Alrighty,...again once more

Voltage Regulators U14, 15, 16, 17 all test correctly.

Q18 (transistor) 32vdc regulator, I read 38vdc the collector, 32.4vdc on the base, and nearly nothing on the emitter.

Diodes 2, 3, 4 and 5 all test good. D3 / R133 junction should read 23vdc but there is nothing there.

The path between the emitter and J-5 is good, 0 ohms, no open ckt.

Now, why don't have anything on the emitter? I could pull Q18 and check it, but rather know for sure before pulling the bottom off as well.

Either way I don't have that transistor in stock so to speak, so I'd be ordering it and I'd rather make sure I order everything I need at once instead of willy-nilly.

Sorry Cohibaman regarding the previous post ,.. I meant to delete it and not post it, but this one instead

[W9TR]

If Q18 is an NPN and there is any load from emitter to ground or a (-) voltage them Q18 is toast.

[macman007]

It's a MPSA 55, PNP according to the On-Semi data sheet. Mouser has them in another brand (Central Semi) @ .46 cents ea....don't know if that means it's toast or not. What do you think?

I hate to waste an order for something, shotgun it and miss..

Thoughts..?

BTW, I appreciate you taking the time to help me with this Cohibaman..,and W9TR.. thank you very much!..

[W9TR]

Without the schematic I can't really help much. If you PM me I'll send you my e-mail address so you can send me the schematic. Good luck!
Tom

[Beowulf62]

Originally Posted by macman007

Q18 (transistor) 32vdc regulator, I read 38vdc the collector, 32.4vdc on the base, and nearly nothing on the emitter.

Diodes 2, 3, 4 and 5 all test good. D3 / R133 junction should read 23vdc but there is nothing there.

The path between the emitter and J-5 is good, 0 ohms, no open ckt.

Now, why don't have anything on the emitter? I could pull Q18 and check it, but rather know for sure before pulling the bottom off as well.

IIRC: For a PNP transistor to conduct the Emitter is always more positive with respect to both the Base and the Collector...or, a Bipolar PNP Transistor will ONLY conduct if both the Base and Collector terminals are negative with respect to the Emitter.



It is much easier to check the solder joints and trace continuity by removing the bottom. I can't say that Q18 is or is not the problem, but I have solved an issue by visually inspecting the solder joints and noticing one that was clearly bad.

[macman007]

@ Beowulf62: I'll get on that today. While I'm there I might pull Q18 and test it then touch up solder joints as well.

@ W9TR: I don't have the option to PM (yet maybe?), unless I've totally forgotten how to use VBulletin....

[Cohibaman]

Originally Posted by macman007

I don't have the option to PM (yet maybe?), unless I've totally forgotten how to use VBulletin....

You need to become a subscriber to PM. Well worth the entrance fee!

[Masterlu]

Originally Posted by Cohibaman

You need to become a subscriber to PM. Well worth the entrance fee!

https://www.audioaficionado.org/payments.php

Indeed