MTC9000 help

[Purity]

Hi guys,

Hope you can help me out?

Basically I got this Electrcoin midi from the barn raid and when I fired it up the monitor was dead. No neck glow at all

First thing I checked was the fuses at F1 and F2 and they are ok

Second thing I checked was the power on the 4 pin connector going into the monitor.

One side read 250v AC, the other side reads 157v AC

I probably didn't need to do this but I also changed the flyback on the chassis

However I am still in the same scenario

Today I thought I would check the B+. Now I've read various methods of doing this so hopefully I've done it right?

1) I connected the red probe to SP3 connection at the chassis and the black probe to the metal chassis. Got a read of 187.3v DC

2) I connected the red probe to SP4 connection at the chassis and the black probe to the metal chassis and got a reading of 29v DC

As a secondary check I put the red probe in the middle holes of the connector on the chassis end into which the scan coils are plugged into, which gave me a reading of 26.3v DC

So from what I've read the low B+ means this can be 3 things:

1) The cap at C34
2) The regulator circuit main power transistor
3) Resistor R110

If it's none of these three then possibly BU508 Transistor

Also I've looked at Randy Fromms flowchart but it doesn't really help me when SP4 is too low and SP3 is too high

I'm not a monitor expert so any help would be appreciated

Purity2014-01-11 15:46:28

 

[Ordyne]

Your b+ is high, what happens if you disable the shutdown?

 

[Purity]

Your b+ is high, what happens if you disable the shutdown?

Thanks Craig for the response

Ok so the correct reading is the 187.3 v DC, which is high. This should be around 130v DC?

Now this is the first monitor I've attempted to repair, so by disabling the shutdown, this is unsoldering one end of the diode at D10 and see if it fires up?
Purity2014-01-11 20:27:39

 

[tb lilley]

Yes to D10.

 

[Purity]

If after unsoldering one end, the monitor fires up, this would confirm a voltage regulator failure?

so I should then test TR19, 20, 21, 22 and ZD3.

Also replace C34

 

[Ordyne]

If you think flow charts fix monitors yes, otherwise that and a whole heap more

 

[Purity]

If you think flow charts fix monitors yes, otherwise that and a whole heap more

This is a starting point to get the monitor firing up. Obviously as I come up against other issues, I'll try and tackle them. The flowcharts and repair guides help to give me, a novice, an idea of where the problems might be, and where to test. It's certainly better than nothing, and I realise they do not comapre to someone with years of experience
Purity2014-01-12 11:25:50

 

[Anthony Graham]

Just a little thought regards the power input to the monitor My inputs on the 4pin are 230v and 120v I know the 250v on yours should be ok as it for the deguass but I am not 100% sure if the input is high for the main monitor circuits as I recall being told it has to be within +10% -20% of spec which is 128v. It won't help the power circuits on the monitor I am sure to be over driven.

maybe of use:
http://pdf.textfiles.com/manuals/ARCADE/A-J/Hantarex%20MTC9000%20%2814-16-20in%29%20%5BService%5D%20%5BEnglish%5D.pdf

I could of course be completly wrong on this as I am still fairly new to it!

Ant

 

[Purity]

I must admit that when I saw the figures I thought they were high. Don't know if they are at acceptable levels.

I remember doing the same thing in 2010 on another cab, and the readings were 225v AC and 135v AC, which is way more acceptable than 250v AC and 157v AC

I might try another multimeter just to confirm those values, as the multimeter I was using today had the battery indicator on, and *might* be giving inaccurate readings

Purity2014-01-12 11:26:42

 

[Purity]

Ok I think I should probably send this for repair?

My multimeter was giving the wrong figures due to the battery, so the AC from the power supply is ok - I think it was 217v AC and 132v AC

However I just tried to read the B+ again and I've obviously shorted something. Fuse F1 blew and its also blown the power supply monitor fuse. I've replaced both but now everytime I connect the monitor it blows the power supply monitor fuse :-(
Purity2014-01-12 13:37:49

 

[Big Phil]

I'm in exactly the same boat with the BombJack I picked up from the raid. No neck glow. I'm also a novice and struggling to troubleshoot.Big Phil2014-01-12 17:04:45

 

[Ordyne]

You could try powering up again with the scan coil connector unplugged, if it still blows the fuse check the large transistor on the side of the chassis heat sink (Tr20) for a short, if that's ok test the 4 diodes that make up the bridge rectifier (d19,20,21,22)

Btw, I wasn't having a pop regarding the flow chart, the problem with them is A) they are now bloody old and were made when half of the faults you see now never happened. B) they miss so much potential stuff out they can lead you into looking in the wrong direction.

Maybe it's time for some upto date ones!

 

[Big Phil]

I can't even find f**king test point 10 !!

 

[Purity]

No worries Craig, I didn't take it as a pop

I think TR20 (TIPL762) is shorted if I have read it correctly?

I read it as B C E in leg order from left to right. I'm getting readings from the meter as

B+ C- = 074
C+ B- = 074
B+ E- = 421
E+ B- = 421
E+ C- =348
C+ E- =348

So that looks shorted

I also looked at the diodes in circuit

D19 = 743
D20 = 749
D21 = 760
D22 = 761
ZD3 = 1015

They only read one way so look like they have not gone open circuit

I checked R105 and got a reading of 347 Ohms between SP3, and SP4

*I've read all these in circuit*
Purity2014-01-13 21:24:09

 

[Purity]

I've also checked the following:

TR19 (BU801) - reading as B C E - Looks shorted? :

B+ C- = 810
C+ B- = Nothing
B+ E- = 917
E+ B- = 932
E+ C- = 923
C+ E- = Nothing

TR22 (BC639) - reading as E C B - Looks shorted?:

B+ C- = 895
C+ B- = Nothing
B+ E- = 902
E+ B- = Nothing
E+ C- = 1322
C+ E- = Nothing

TR21 (BF422) - reading as E C B - Looks ok:

B+ C- = 950
C+ B- = Nothing
B+ E- = 980
E+ B- = Nothing
E+ C- = Nothing
C- E+ = Nothing

*I've read all these in circuit*
Purity2014-01-13 21:26:32

 

[Purity]

Also checked the HOT in circuit TR15 (BU508A) read it as B C E

B+ C- = 140
C+ B- = 140
B+ E- = 006 with continuity
E+ B- = 006 with continuity
E+ C- = 124
C+ E- = 122

so that looks screwed

Also I've noticed that Cap C57 had a broken leg so I've soldered that back

I also checked TR17 (BDX 53 A) while at it. Read as B C E that looks shorted?

B+ C- = 883
C+ B- = Nothing
B+ E- = 1011
E+ B- = Nothing
E+ C- = 620
C+ E- = 791
Purity2014-01-14 08:11:30

 

[pulstar]

I would take the transistors out of circuit to test. They can (and often do) give false readings when tested in circuit.

 

[Purity]

I would take the transistors out of circuit to test. They can (and often do) give false readings when tested in circuit.

Yup, I probably need to lift a leg on the diodes to confirm results aswell?

 

[pulstar]

Yeah, that would definitely give you a more accurate result.

 

[Purity]

I'm also not totally convinced I've read the transistors correctly. Maybe someone can confirm before I start replacing them?