700B blew one Right channel 5A supply fuse

[62vauxhall]

Should have bought a DMM today after all. If testing the output transistor testing requires voltage, would a meter that takes a 9V battery be preferable to one that takes two AA's?

I did look today at multimeters available at the places where I went fuse shopping but was unimpressed with those in the under $50 range. I made the mistake of watching a YouTube "Cheap Multimeter Shootout" this morning before I left so had their two top picks in mind, Extech and Amprobe. Only Extech is sold by locally and the EX330 model in question is $75 CDN.

It uses two AA batteries and it seems the Brand "X" cheapies I saw today took 9V.

 

[laatsch55]

The little craftsman I have takes a 9. It must have a diode test fearure, for thats the junctions you are testing in transistors. Any DMM that has a diode test would work...

 

[laatsch55]

Gary, you shouldn't have to spend more than 50.00 for a DMM capable of testing diodes....

 

[62vauxhall]

Bear in mind that I'm in Canada where stuff is expensive because import duties and tariffs are high. Plus, there are nowhere near the number of retailers here as there are in the US so they can charge whatever they want. Sometimes I do buy online from the States because plain and simple, whatever I'm after doesn't exist here and in those cases, shipping, duty and sometimes brokerage fees are moot points.

If I were to pay $75 here for something that sells in the US for $55, which the Extech does, it would be cheaper for me to do that than to have one sent. A retailer on Amazon has those Extechs on sale for $50 with free shipping but only to a US address. An E-bay retailer has them also for $56.63 with free shipping but again to within the US. Shipping to my Postal Code in Canada is $36.60.

One meter I saw today for $45 CDN was a brand called Uni-t with Chinese text on the box. When I got home, I looked it up and it does have some credibility. Online, they sell for about $20 USD but most US vendors won't ship to Canada and those that do, charge an arm and a leg. If I were to order one, it would wind up being $45 anyway. If I were to drive back to Vancouver to get that one, the round trip is 3 hours and I would burn about $10 of fuel.

I'm going to bite the bullet tomorrow on the $75 Extech and post once I have it. Hopefully you'll be willing to explain to me how to use it on this 700B.

There does not seem to be much middle ground for multimeters in this neck of the woods. Getting one for $12 is easy but the next stop is mostly well North of $100.

 

[laatsch55]

Gary, there are some guys here that have a system. We ship to Sumas, Wa then it's hand delivered into Canada. Check with fitz43, and lyle.... both have Sumas shipping addresses...

And I'll be glad to help you with the 700....

 

[62vauxhall]

Coincidental that you mention Sumas because I have used Package Express there as a destination shipping address. Usually I drive to the border and walk across. Unfortunately my passport was about to expire so I took it in for renewal a couple of days ago. What's unfortunate is that because there was a typo on my old one, I had to relinquish it for them to destroy. ETA on the new one is several weeks and I cannot cross the border until I get it.

What you say is interesting though, what sorts of things get shipped to Sumas?

 

[laatsch55]

Need some pics of the inside too Gary, see which board ya got and some other clues....

 

[laatsch55]

Here ya go Gary......http://www.iavscanada.com/

 

[62vauxhall]

Had to dig out the old 3MP camera, my newer one's battery is dead.

*The board is a 14A date stamped May 2, 1974.
*Right channel (the bad one) output devices are 10 Motorola MJ15024 and 2 RCA 410.
*Left channel output devices (still good I think) are 10 Phase Linear XPL909 and 2 RCA 410.
*S/N is 574-0878
*Blue capacitor is a Mallory 10,000Mf 100V installed in 2010.

I thought both of those capacitors are replaced as a matter of course but at the time, the tech said only one was needed. That's always bothered me and made me wonder if was the remaining original one that packed it in and is causing or has caused this latest problem.

Anything else I can tell you, let me know.

 

[fitz43]

Here ya go Gary......http://www.iavscanada.com/

From the announcement on the site, Bob Carver will be in attendance at this years Garage Sale.

 

[laatsch55]

Gary, with you taking pictures like that, we'll get ya fixed up. The right channel doesn't work correct? There are 2-TO-220 form factor transistors where there should be some TO-39's. Q7,Q10 need to come out and be tested. I have spares if they are bad. Those 220's need to stay out anyway. And get a big cap ordered to match the new blue one. Gotta head to the field, so I'll be gone for a few tours...

 

[62vauxhall]

I now have a multimeter and identified the TO220 transistors you refer to. Can you say what TO39 transistors I need to replace them with? Or did you mean pull them and and not replace them with anything?

Also identified Q7 & Q10 - pulled, tested and both OK.

In a different forum, you mentioned replacing Q10 with a 2N3439 and Q7 with a 2N55416. In case I have difficulty getting those short lengths of pin back in the holes, would it be wise to find those substitutes?

Seems I can get a duplicate to the blue Mallory cap from an online vendor delivered to me in two days for $58. That's less than the $65 a local shop would charge to special order one and it would take longer.

Am going to wait a day or two before ordering just in case IA finds some in all those parts they bought from a repair shop. It was the shop that last fixed this amp, where only a single capacitor was replaced. When I picked up the fixed amp in 2010, I remember seeing the box of caps with one missing. I thought that maybe, since IA now has the entire parts inventory, that box of caps might be in their possession.

In any case, I shall have another cap next week.

 

[Skynyrd77]

I now have a multimeter and identified the TO220 transistors you refer to. Can you say what TO39 transistors I need to replace them with? Or did you mean pull them and and not replace them with anything?

Also identified Q7 & Q10 - pulled, tested and both OK.

In a different forum, you mentioned replacing Q10 with a 2N3439 and Q7 with a 2N55416. In case I have difficulty getting those short lengths of pin back in the holes, would it be wise to find those substitutes?

Seems I can get a duplicate to the blue Mallory cap from an online vendor delivered to me in two days for $58. That's less than the $65 a local shop would charge to special order one and it would take longer.

Am going to wait a day or two before ordering just in case IA finds some in all those parts they bought from a repair shop. It was the shop that last fixed this amp, where only a single capacitor was replaced. When I picked up the fixed amp in 2010, I remember seeing the box of caps with one missing. I thought that maybe, since IA now has the entire parts inventory, that box of caps might be in their possession.

In any case, I shall have another cap next week.

love your avatar.lost in that damn ozone again lol. your fitting right in here

 

[laatsch55]

The 39 and 5th are no longer available. When we get done testing the test of the board whatever you need I have a lot of.
Begin by testing every transistor on the right side of the board. We're just looking for shorts on a quick run through. Check the service manual for some more info. Q1, q2 are npn, q3, q4 are pnp. Q5-npn. Q7 pnp. Q10 npn. Run through those right quick and see if they are shorted. In circuit is OK right now.

 

[62vauxhall]

Q7 & Q10 are off the board and tested OK.

Q5 is in the board and tested OK.

Q3 is in the board and I got readings E to C & C to E so I assume it's NFG.

QI & Q2 are a bit of a mystery. According to the schematic, they are supposed to be T1597's but there are no such transistors on the board. There are however, two MPS5172's.
Assuming MPS5172's (they are also NPN) were subbed fo T1597's, they don't test well so must also be NFG.

Q4 is an an even bigger mystery. Schematic says it should be an MPSA93. Not only is there no such transistor on the board, the schematic counts 10 transistors for the right channel and I physically count 9.

The schematic I'm using was part of the service manual downloaded form HiFi Engine, page 1 of which clearly states it is for Phase Linear 700 and 700B.

The Schematic is dated Sept, 9, 1974 and the board is dated May 2, 1974. Is it likely there were modifications between those dates?

I think there are other differences in the transistor compliment on the board compared to the schematic but they are not transistors on your to check list.

 

[laatsch55]

The difference on NPN and PNP transistors will necessitate changing the leads to determine if they are shorted. NPN requires the base to have the positive lead and PNP to have the negative lead on the base. 5172's were standard for a time. Q5 is the big heatsinked one. Q8,Q9 are the 2N1304, and 2N1305's the protection transistors and are germanium and will read lower accross their jct's , typically .16-.20..VoltsDC. Q6 is the bias transistor in the small P-strap on the backwall between the transistor rows...What readings are you getting with what leads where in diode test mode?

 

[laatsch55]

Q4 is on your board Gary, right next to Q3. Q3 should either be TIS93, or GES93, it may also be MPSA 93 in some cases.

 

[62vauxhall]

I cannot see any transistor on the back wall between transistor rows and don't know what a P strap is. I see resistors between the transistor rows, lots of them and also two black squat cylindrical devices bolted on the wall stamped "Elmwood Sensors".

The meter was in Diode Test mode and below is the procedure I followed, it seemed quite concise. I did not think to make note of the exact readings because those that checked good were within the parameters stated below - 0.45V to 0,9V. Give or take around .7V.

What details I have are at the end of this post.

Step 1 - BASE to EMITTER
Hook the positive test lead from the multimeter to the BASE of the transistor. Hook the positive meter lead to the EMITTER of the transistor. For any good NPN transistor, the meter should show a voltage drop between 0.45V and 0.9V. If you are testing a PNP transistor you should see "OL".

Step 2 - BASE to COLLECTOR
Keep the positive lead on the BASE and place the negative lead to the COLLECTOR.

For a good NPN trasistor, the meter shouild show a voltage drop between 0.45V and 0,9V. If your are testing PNP transistors, you should see "OL"

Step 3 - EMITTER to BASE
Hook the positive lead from the multimeter to to the EMITTER of the transistor. Hook the negative meter lead to the BASE of the transistor.

For any good NPN transistor you should see "OL". If you are testing PNP transistors the meter should show a voltage drop between 0.45V and 0.9V.

Step 4 - COLLECTOR to BASE
Hook the positive lead from the multimeter to the COLLECTOR of the transistor. Hook the negative meter lead to the BASE of the transistor.

For any good NPN transistor you should see "OL". If you are testing PNP transistors the meter should show a voltage drop between 0.45V and 0.9V.

Step 5 - COLLECTOR to EMITTER
Hook the positive meter lead to the COLLECTOR and the negative meter lead to the EMITTER. A good NPN or PNP transistor will read "OL". Swap the leads and once again a good NPN or PNP transistor should read "OL".

I performed every step on all specified transistors with the following results.

Q1 & Q2 (or so I believe) the MPS5172 transistors - On one, do not know which, the reading was not "OL" with positive meter lead to COLLECTOR and negative lead to EMITTER. The reading fluctuated quite a bit before settling at "0.000" - not "OL". One of these is BAD. I tried this a few times with the same results. It's counterpart tested fine.

Q3 - there was a reading with positive to EMITTER - negative to COLLECTOR and visa versa. It should have read "OL". It's BAD.

Q4 - Did not test - still looking for it. If it is one of the TO220 transistors, what's on the board are an MPSU10 and an MPSU60 not TIS93, GES93 or MPSA93.

Q5 - tested good.

Q7 - tested good (out of circuit).

Q10 - tested good (out of circuit).

Did not test (not on the check list) but I found Q8 & Q9 and they are what what you say 2N1304 & 2N1305.

 

[NavLinear]

I cannot see any transistor on the back wall between transistor rows and don't know what a P strap is. I see resistors between the transistor rows, lots of them and also two black squat cylindrical devices bolted on the wall stamped "Elmwood Sensors".

If you look at photo #5 in post 49 you will see two sets of wires (black, white and red) that come from the back of the controller board to the back wall of the chassis. These wires are connected to the bias transistors and attach to the chassis with a "P" strap.

 

[62vauxhall]

Thanks for clarifying, I misunderstood by expecting transistors to be on the back wall. I now see the transistors those wire bundles connect to are 2N1304's. There is one of those transistors in the schematic at Q8 position. I tested it in circuit and it failed on more than one step. If nothing else, there was about .750 between EMITTER - COLLECTOR and same with reversed leads where it should have been "OL".

I checked the transistor immediately next to it, a 2N1305 and got bad readings. Where "OL" would be good, the meter ranged before settling on 0.000 or very slightly higher like 0.004. On the schematic, a 2N1305 is in the Q9 position.

So it seems Q8 & Q9 are bad.