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MC2500 Lamp Functionality Question

bhuskins

bhuskins

Super Member
MC2500 works fine with no real issues. But the left channel normal operation lamp does not work. The right channel normal operation lamp works fine. Obviously, my 1st thought was to replace the lamp. While I had the board out, I went ahead and replaced all 4 lamps (Power Guard R&L Normal Operation/Limit Bulbs) with the proper 14v 80ma JKL7382 bulbs. The problem is still persistent in the left channel with the bulbs replaced.

There's really nothing else on the lamp board other than traces and they all check out. The connector from the lamp board connects to the power guard display drive board which looks to be fairly straight forward.

Are there any known issues on this board? Looks like for the left channel channel driver section I should focus on R801~R805 and Q801~Q803 on the power guard display driver board. Any suggestions?

Resistors
R801 - 100K ohm, 1/4 watt
R802 - 47K ohm, 1/4 watt
R803 - 680 ohm, 1/4 watt
R804 - 470 ohm, 1/4 watt
R805 - 470 ohm, 1/4 watt
Transistors
Q801 - Si, PNP, Darlington, MPS-A64 (610-MPSA64 mouser replacement)
Q802 - Si, Triac, IB200-1 (unknown replacement)
Q803 - Si, Triac, IB200-1 (unknown replacement)
 
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OK...so I pulled all of the resistors and they were all testing spot on (off the board) and they were reinstalled to the board. I also replaced Q801 because I had one on hand. With the boards reinserted, the problem persists.

One thing to note, when the unit is powered up (when completely cold), the limit lights on both channels turn on (very briefly...just a flicker basically) and then the normal operation lamp comes on for the right channel only. My understanding is that this is what is supposed to happen upon start up so it really is just the normal operation lamp that has the issue.

Any ideas?

Any suggestions for a replacement for Q802 & Q803? Should I be looking somewhere else?

All help is appreciated :yes:
 
I had a similar problem on a MC2205 ages ago and it ended up being a faulty transistor. Honestly, I cannot remember which one I replaced but I'd say you're on the right track. I do remember that I obtained a suitable replacement at Radio Shack believe it or not.
 
Just need to get a good suggestion for what to use for the triacs if that's what is needed to be replaced. I'm also positive it's not the bulb being that I've swapped in and out known good ones. If it's not the triacs it would have to be something else outside that area of the schematic I would guess.
 
Still looking for a replacement on the triacs...would there be information anyone would need to help suggest a substitute? Help! :-)
 
I really wish I could help as I recently had the same problem occur on my 2500. The led lights were replaced along with a recap about a year ago and I'm hoping it's just the bulbs being burnt out. But taking a 2500 apart and chasing down the problem is waaayy beyond what I'm capable of. I'll take a deep breath and bring the monster to my very capable tech and let him diagnose.
I wonder if the op has found the problem yet?
 
I tested all 4 of the IB200-1 triacs (Q802, Q803, Q805, Q806 also known as 131-011 or MAC91A-1) all 4 removed from the circuit. 3 of them tested the same and one tested open in all 5 connection combinations. The bad one came from left channel circuit (Q803 to be exact) so I'd expect it to be the culprit.

Can someone suggest a modern replacement for these triacs?

The MAC91A-1 shows to be this...

V(DRM) Max. (V) : 30
I(T(RMS)) Max. (A) : 800m
@Temp. (шC) (Test Condition) : 60#
I(TSM) Max. (A) : 8.0
@ t(w) (s) (Test Condition) :
I(GT) Max. (A) : 10m
V(GT) Max.(V) : 2.0
I(H) Max. (A) Holding Current : 10m
I(D) Max. (A) Leakage Current : 500u
@Temp. (шC) (Test Condition) : 110х
V(T) Max. (V) : 1.5
@I(T) (A) (Test Condition) : 1.1
dv/dt Min. (V/us) : 25
t(gt) Typ. (s) : 2.5u
@I(T) (A) (Test Condition) : 1.1
dv/dt(c) Min. (V/us) : 2.0
dv/dt Min. (V/us) : 25
Minimum Operating Temp (шC) : -40
Maximum Operating Temp (шC) : 110х
Package Style : TO-92
Mounting Style : T
 
What about mouser ########## for a replacement?

SEE BELOW FOR THE SOLUTION
vvvvvvvvvvvvvvvvvvvvvvvvvvvv
 
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Replacing Q803 did in fact correct my problem...I went ahead and replaced all 4 triacs (Q802, Q803, Q805, Q806) since I sourced them and I figured it best to keep all 4 the exact same. All 4 lights are operating properly now.

I ended up using Mouser Part #: 771-MAC97A8 which seems to be the best match currently available.

Hopefully my 1 man show here will help someone someday :-)
 
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I know its an old thread, but also just to help others in the future, 131-011 is also used in the MC7270, and one was shorted in a unit I am working on. I cant find any of the MAC91A-1 listed as official replacement. HOWEVER, littlefuse is sold by Mouser, and they list a factory approved direct substitute of LX807DE. Available in large quantities at this time at $0.45 each. Drop in replacement that worked perfectly. It is for a switch for PG lamps on the MC7270.
I reiterate the statement above that I hope this helps someone with a search in the future.
 
Thanks to the above AK member's.

LX807DE worked for me in my MC2255. I had one limit lamp not coming on. I first swapped the triacs left with right to confirm the triac was the issue. Replaced both left and right limit triacs so they match. I didn’t replace the normal lamp triacs, but I bought extras just in case.
 
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