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

[macman007]

OK, here's what I have so far.

The ribbon cables are and were installed properly. I cleaned contacts on the cables and sockets J1, J8, J2, J3 (ground) and CX171.

Next, I inspected the cables themselves, all contacts on both cables have 100% continuity from end to end. Checked the J3 ground, tight and 0 ohms resistance.

Socket's J1-J8: Pins 1,5,7,11 have a ground as shown. Pin 10 5vdc present and Pin 12 has 3.2vdc present as indicated on schematic.

Socket's J2- CX171, Pins 4, 11, 15 have grounds as shown, Pins 2,17 5vdc as shown, pin 16 reads 3.3vdc as shown.

So far nothing is showing bad. I performed the wooden dowel test, pressing gently on the circuit boards, as well as the wiggle test looking for any poor connections, cold solder joints, etc.

Nothing is sticking out as bad, and the Vacuum Fluorescent Display is still dead as a doorknob, no flickers, or indications of life. The VF display is McIntosh part# 310346, I'd have to check Audio Classics or call Mc on Monday, but I'm still not 100% sure its the VFD. All controls and button command communication is 100% working, as are is the fibre optic faceplate lighting.

The other possibility is U1 on the schematic which is the 5X7 DOT CHARACTER DISPLAY DRIVER, McIntosh part# 310145. Unless it's some odd component failure from ESD due to vacuuming. I don't want to throw parts at it, I try to 100% prove a diagnosis before purchasing and swapping in and out parts.

This has got me a little stumped at the moment. Anyone have any thoughts

[piolaxo]

Have you checked J1:12? That should be -32V; that is the power supply to the
display controller. Another thing to check is all the outputs from the regulators:
U14, U15, U16 and U17. If they are okay, then the problem may be closer to the
display board.

[W9TR]

VFD’s have a filament. Is it intact? You should be able to see it glowing in a very dark room. That would be my bet at this point as you have exhausted pretty much everything else.

[macman007]

Originally Posted by piolaxo

Have you checked J1:12? That should be -32V; that is the power supply to the
display controller. Another thing to check is all the outputs from the regulators:
U14, U15, U16 and U17. If they are okay, then the problem may be closer to the display board.

I have an off day tomorrow (Monday), so after I make progress on some customer stuff, finish and prepare to ship, I'm going to dig in and check the components you listed above. ON the -32 volt J1 : J12 , It reads -32vdc in the schematic, however I read 3.2vdc. I thought perhaps that 32vdc is a misprint and it was actually supposed to be 3.2vdc. Do we know for sure if it's 3.2 or 32 VDC?

Originally Posted by W9TR

VFD’s have a filament. Is it intact? You should be able to see it glowing in a very dark room. That would be my bet at this point as you have exhausted pretty much everything else.

I can't tell if the filament is intact or not,. However all lights out in the dark room, unit powered up, there is zero light emitting from anywhere on the VF display. The faceplate fiber optic/ led illumination is working 100%, as are all controls on the front. That was one of the things I first looked at initially, thinking the same thing.

I do need to clear up as to whether the J1 pin J12 is supposed to measure 3.2vdc or -32vdc. My brain is telling me there should also be +32vdc on another pin or +3.2vdc as well as -3.2/32vdc, measured to ground for the + and - voltage supply.

It would be odd for the actual voltage to spec at -32vdc and I measure 3.2vdc. Misprint perhaps? Do we know that it is 100% supposed to measure 32vdc? I had that thought when I first measured against the schematic specs, and it wouldn't be the first time a schematic was misprinted. I've been down similar alleys before with other gear, but I'd think a company prestigious and exacting as McIntosh would not make that type of published mistake.

You never know until you know.

My continued thanks to everyone for their help. I have no doubts that between us all, we'll get to the bottom of this and get her display up and running very soon!

[piolaxo]

Originally Posted by macman007

I have an off day tomorrow (Monday), so after I make progress on some customer stuff, finish and prepare to ship, I'm going to dig in and check the components you listed above. ON the -32 volt J1 : J12 , It reads -32vdc in the schematic, however I read 3.2vdc. I thought perhaps that 32vdc is a misprint and it was actually supposed to be 3.2vdc. Do we know for sure if it's 3.2 or 32 VDC?


I can't tell if the filament is intact or not,. However all lights out in the dark room, unit powered up, there is zero light emitting from anywhere on the VF display. The faceplate fiber optic/ led illumination is working 100%, as are all controls on the front. That was one of the things I first looked at initially, thinking the same thing.

I do need to clear up as to whether the J1 pin J12 is supposed to measure 3.2vdc or -32vdc. My brain is telling me there should also be +32vdc on another pin or +3.2vdc as well as -3.2/32vdc, measured to ground for the + and - voltage supply.

It would be odd for the actual voltage to spec at -32vdc and I measure 3.2vdc. Misprint perhaps? Do we know that it is 100% supposed to measure 32vdc? I had that thought when I first measured against the schematic specs, and it wouldn't be the first time a schematic was misprinted. I've been down similar alleys before with other gear, but I'd think a company prestigious and exacting as McIntosh would not make that type of published mistake.

You never know until you know.

My continued thanks to everyone for their help. I have no doubts that between us all, we'll get to the bottom of this and get her display up and running very soon!

Hi again, no it is not a misprint. It is -32V. If you search for OKI ML9207
5x7 Display Controller manual, you will find that the VFD supply ranges
from -20V to -60V. So -32V is right in the range.

You should check not only the regulators, but the diodes feeding the
regulators. It is a power supply issue for sure. The display should be okay.

Sal

[macman007]

Will do. I was trying to locate the spec page for the 5x7 display controller but couldn't figure out how to narrow the search parameters online to get it.

OK, good show, Sal (piolaxo). At least now I know it's a PS issue, and almost 100% the 32 volt regulator or diode(s). I've never had a diode die from ESD, but I'm sure it's entirely possible. Looks like Q18's 32vdc output ,or what feeds it/ steps up the 23vdc feed is the cause.

The PS / regulators in question appear on the left hand side of the upper board, where most of the other main PS resides.

I would never have thought with wearing a ground strap, that using a vacuum to suck the debris out would have hurt the circuit. I was using a small paint brush while sucking the garbage out. Either way it's 100% that's what is the root cause. Boy I'm stupid..

From now on, canned air only, and no brushing, even strapped in. Fingers crossed it's only the regulator Q19, not something else. That said, it's a fair possibility I have the diodes 'in stock', but probably not the regulator. They are typically inexpensive at Mouser.

Now all I have to do is locate the sucker causing the problem.

[Beowulf62]

You might also inspect with a jeweler's loupe...circuit board traces and solder joints...looking for breaks, small cracks and or dull solder connections. Under the board as well. The diodes and regulator may be functional, but a bad solder joint may have lost proper contact due to vibration/movement during cleaning. This may not have been discovered/resolved by pushing on components or the board.

[macman007]

Thank you Beowulf62, I will add that to the list of things to check while I have it open. I'm thinking its the 32 volt dc regulator circuit, but you are right, a cold solder joint or other board issues around components may be the culprit.

Once I make measurements at the -32vdc regulator and associated components it should reveal the issue. There is definitely no -32vdc at the J1 connector to the face at either end of the ribbon.

A cold solder joint at a diode or other component would make things simpler, as long as it's easy to locate. McIntosh historically has good quality soldering and QC, but if they are using that lead-free garbage solder, that stuff is known to cause all types of connection, issues as its harder to work and less hearty with, IMO.

I only use old school solder, containing lead, tin, and silver. I don't have near as many issues with it. Lead-free stuff is garbage. IDC about health issues, just don't breath the stuff while soldering, good ventilation and a fan keeps it out of my face and lungs...

[Beowulf62]

Yup, the good ol' stuff is the way to go.... I use a McIntosh RCT-4 Remote Control Translator Repeater in my system and picked up a spare years ago. When it arrived it was dead. I was about to send it back, but decided to open it up and check...there was the problem: a bad solder connection at the DC power input jack. No amount of wiggling changed the problem. As noted previously, unusual for cleaning to cause a component failure...but compromised contact integrity could easily happen. I'll keep my fingers crossed for an easy fix...

[macman007]

Thanks Beowulf!