EIP 578 - A106 board - CR4 tunnel diode equivalent? - Page 1
Forum section: electronics / repair

author: John_ITIC
author_rank: Frequent Contributor
timestamp: November 09, 2020, 02:49:54 am
content: Hello, I'm restoring an EIP 578 counter that doesn't count. Having followed the troubleshooting guide in the service manual, I found that the A106 board does not have any voltage across CR4 but should have 500 mV across (per service manual). CR4 is a switching tunnel diode and it measures about 3 Ohm both directions, out of circuit, with both 0.1mA and 1mA test currents of my Fluke 8846A. So, the diode seems shorted. I'd like to find a suitable replacement.This is what I know:Ref des Description EIP No. Units / assembly Typ Mfg No Typ FSCM No.CR4 Tunnel, switching 2710033 1 G0010C 20754FSCM : Federal supply code for manufacturerI cannot get any luck on Google with any of these part numbers. The part is socketed so I assume a Germanium diode (heat sensitive).Can anyone, based on the application, suggest a suitable replacement?There are some that look like germanium on Ebay but i'm not sure which is the best choice. Given the prices, I don't want to buy too many just to try...https://www.ebay.com/itm/Tektronix-152-0125-01-tunnel-diode-4-7-mA-15-pF-FREE-shipping-new/164321671309https://www.ebay.com/itm/1N3713-TUNNEL-DIODE/264922830554https://www.ebay.com/itm/1N3717-TUNNEL-DIODE/264922832262https://www.ebay.com/itm/1N3718-TUNNEL-DIODE-NEW-USA-SELLER-FAST-SHIPPING/323763775503The 1N371X seems like a good replacement but which current capability is ideal? I would assume that a larger current capability results in a lower switching frequency.http://w140.com/tekwiki/images/3/3d/1N3718-GPD_Optoelectronic_Devices.pdfThanks,/John.

author: HighPrecision
author_rank: Unknown
timestamp: November 10, 2020, 12:40:30 pm
content: At startup (power-on) and NO input signal, check the voltage drop on R13 (43 Ohm 2%) for about 0.6Vdc, Tunnel diode require a DC current flowing to be near the switching point (about 10mA), if the DC voltage on this diode is about 0.28Vdc this is probably OK.

author: factory
author_rank: Super Contributor
timestamp: November 10, 2020, 08:44:56 pm
content: I looked up the part number 2710033 and noticed there is a 2710033-00 version, no idea if this is a later replacement for an obsolete part or not, but it does have data suggesting 20mA;https://www.parttarget.com/5961-01-369-4056_5961013694056_2710033-00.html/-7E6B32C7-6920-4607-A02D-64B04B3AF880You really need something like a curve tracer to test tunnel diodes, they are very easy to damage with other methods.And yes they can also be damaged by too much heat, hence why it's socketed, in some older HP TE they soldered them in & a later service note advises fitting sockets if they are replaced.David

author: texaspyro
author_rank: Super Contributor
timestamp: November 11, 2020, 07:23:48 am
content: Be careful of Russian tunnel diodes... a lot are gallium arsenide. The 20mA ones work in Tek 1502 TDRs, but the output level is rather high and you need to tweak the TDR output amplifier stage.

author: John_ITIC
author_rank: Frequent Contributor
timestamp: November 12, 2020, 04:05:13 am
content: Thanks Everyone. I ordered the 1N3713 and 1N3717 so I can give it a try. With the old diode, or some other I found (not tunnel diode), I could not see any 50 MHz test signal at all across CR4. I'm feeding in an 800mVpp / 50 MHz signal on A106-J1. So I'm checking all parts in the signal path to see what I can find.../John.

author: HighPrecision
author_rank: Unknown
timestamp: November 12, 2020, 07:13:11 am
content: Quote from: John_ITIC on November 12, 2020, 04:05:13 amThe default power-on is on Band 3, the related connector is A106-J2For J1 input manually select Band 2

author: John_ITIC
author_rank: Frequent Contributor
timestamp: December 21, 2020, 02:44:36 am
content: I found a replacement A106 board on Ebay for $25 and that fixed the issue. My 578 is now back in good working condition.I'm still not sure what the problem is with my original A106 board. Given that the 578 is now working, I doubt I will spend further time troubleshooting the original board.Thanks all for your help./John.